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'''Clapham Park''' is an area in the [[London Borough of Lambeth|Borough of Lambeth]] in [[London]], to the south of central [[Clapham]] and west of [[Brixton]].
{{pp-semi-vandalism|expiry=November 2, 2008}}
{{otheruses}}
[[Image:Brain 090407.jpg|thumb|right|238px|[[Human brain]]]]


The original Clapham Park estate was a speculative development by [[Thomas Cubitt]], who bought {{convert|229|acre|km2}} of Bleak Hall Farm in 1825, and marked out plots for building around the new broad, tree-lined streets of Kings Avenue, Clarence Avenue, Poynders Road and Atkins Road. It was planned to consist of extremely large detached houses in Cubitt's characteristic [[Italianate architecture|Italianate]] villa style, set in extensive grounds.
The '''brain''' is the center of the [[nervous system]] in animals. All [[vertebrate]]s, and the majority of [[invertebrate]]s, have a brain. Some "primitive" animals such as [[cnidarian|jellyfishes]] and [[echinoderm|starfishes]] have a decentralized nervous system without a brain, while [[sponge]]s lack any nervous system at all. In vertebrates, the brain is located in the head, protected by the [[skull]] and close to the primary sensory apparatus of [[Visual perception|vision]], [[Hearing (sense)|hearing]], [[equilibrioception|balance]], [[gustation|taste]], and [[olfaction|smell]].


However, the ambitions of the developer were never fulfilled, and some plots remained undeveloped at the outbreak of [[World War I]]. Cubitt's own residence, Lincoln House, with its vast grounds, was demolished in 1905.
Brains can be extremely complex. The [[human brain]] contains roughly 100 billion [[neuron]]s, linked with up to 10,000 [[synapse|synaptic]] connections each. These neurons communicate with one another by means of long protoplasmic fibers called [[axon]]s, which carry trains of signal pulses called [[action potential]]s to distant parts of the brain or body and target them to specific recipient cells. Charles Sherrington, a pioneering investigator of brain function, visualized the workings of the brain in action in poetic terms:


'''Rodenhurst Road''', a street of large double-fronted semi-detached [[Edwardian]] houses was laid out on the site of Lincoln House. British statesman [[Arthur Henderson]] once lived at number 13 and there is a [[Blue Plaque]] on the house indicating this. Because of its leafy layout, Rodenhurst Road is often erroneously assumed to have been an original part of Cubitt's layout. The undivided properties remain among the most expensive in Lambeth.
{{cquote|The great topmost sheet of the mass, that where hardly a light had twinkled or moved, becomes now a sparkling field of rhythmic flashing points with trains of traveling sparks hurrying hither and thither. The brain is waking and with it the mind is returning. It is as if the Milky Way entered upon some cosmic dance. Swiftly the head mass becomes an [[enchanted loom]] where millions of flashing shuttles weave a dissolving pattern, always a meaningful pattern though never an abiding one; a shifting harmony of subpatterns.|20px|20px|C. S. Sherrington|<ref>[[#refSherrington|Man on his nature]]</ref>}}


'''Severance of the estate'''
From a philosophical point of view, it might be said that the most important function of the brain is to serve as the physical structure underlying the mind. From a biological point of view, though, the most important function is to generate behaviors that promote the welfare of an animal. Brains control behavior either by activating muscles, or by causing secretion of chemicals such as hormones. Not all behaviors require a brain. Even single-celled organisms may be capable of extracting information from the environment and acting in response to it.<ref>[[#refGehring|Gehring, 2005]]</ref> Sponges, which lack a central nervous system, are capable of coordinated body contractions and even locomotion.<ref>[[#refNickel|Nickel, 2002]]</ref> In vertebrates, the spinal cord by itself contains neural circuitry capable of generating reflex responses as well as simple motor patterns such as swimming or walking.<ref>[[#refGrillnerWallen|Grillner & Wallén, 2002]]</ref> However, sophisticated control of behavior on the basis of complex sensory input requires the information-integrating capabilities of a centralized brain.


From the 1920s, some of the undeveloped plots on the southern part of the estate were developed with medium-density terraced and semi-detached houses for sale. With the adoption of Poynders Road as the arterial "South Circular" road, this area is now severed from the area further north by traffic, and not generally referred to as part of Clapham Park. The site of one Cubitt villa was donated to the then Metropolitan Borough of Wandsworth as a park, and is now known as '''Agnes Riley Gardens''' after its benefactor.
In spite of rapid scientific progress, the way that brains work remains in many respects a mystery. The operations of individual neurons and synapses are now understood in considerable detail, but the way they cooperate in ensembles of thousands or millions has been very difficult to decipher. Methods of observation such as [[EEG]] recording and [[neuroimaging|functional brain imaging]] tell us that brain operations are highly organized, but these methods do not have enough resolution to reveal the activity of individual neurons. Thus, even the most fundamental principles of neural network computation may to a large extent remain for future investigators to discover.<ref>[[#refSystems|23 Problems in Systems Neuroscience]]</ref>


'''The Clapham Park Estate'''
This article examines the brains of all types of animals, including humans, in a comparative way: it deals with the human brain to the extent that it shares properties with the brains of other species. For an account of features that only apply to humans, see the [[human brain]] article.


The area immediately to the east of the estate had been developed by the [[London County Council]] (LCC) in the 1920s as [[council housing]], mostly in characteristic blocks of [[neo-Georgian]] brick flats. Following [[World War II]] most of the Cubitt houses were demolished and the northern part of the original area was redeveloped by the LCC to a very different [[Modern Movement]] style. Most buildings are set on an arbitrary diagonal axis to the existing street line, and visitors to this part of the estate get easily lost. Following completion of the scheme by the [[Greater London Council]], the Clapham Park Estate became the largest single council estate within the new London Borough of Lambeth.
==Structure of the brain==
===General anatomy===
[[Image:ComparitiveBrainSize.jpg|thumb|right|300px|Brains of 8 species of mammals]]
The human brain weighs about three pounds, or 1.5 kg.<ref>[[#refPrinciples|Principles of neural science]], Ch. 17</ref><ref name=CarpenterCh1>[[#refCarpenter|Carpenter's Human Neuroanatomy]], Ch. 1</ref> In its natural state it is very soft, having approximately the consistency of pudding, although surrounded by leathery membranes. When alive it is pinkish on the outside, and mostly white on the inside, with subtle variations in color. The brains of other species have generally similar properties, but smaller sizes in relation to the body.


Lambeth Council also constructed flats west of Clarence Avenue, including three tower blocks (Barnsbury, Belgravia and Bloomsbury houses) commemorating Cubitt's more successful developments.
The largest part of the human brain is the cerebral hemispheres, situated at the top and covered with a convoluted [[cortex]].<ref>[[#refPrinciples|Principles of neural science]], p 324</ref> Underneath the cerebrum lies the [[brainstem]], appearing somewhat like a stalk on which the cerebrum is attached. At the back of the brain, beneath the cerebrum and behind the brainstem, is the [[cerebellum]], a structure with a horizontally furrowed surface that makes it look different from any other brain area. In other mammals, the same structures are present, but the cerebrum is not so large in relation to the brain as a whole. As a rule, the smaller the cerebrum, the less convoluted the cortex. The cortex of a rat or mouse is almost completely smooth. The cortex of a dolphin or whale, on the other hand, is more convoluted than the cortex of a human.


The Clapham Park Estate has had a concentration of social problems, which were not recognised statistically while the estate was divided between three local government wards. The estate was served by very few community facilities, and this was exacerbated by Lambeth's closure of the branch library in 2000. The journalist and commentator [[Polly Toynbee]] lived in a "hard-to-let" flat on the estate while researching her 2003 book ''Hard Work: Life in Low-Pay Britain''
In vertebrates, the brain is surrounded by [[connective tissue]]s called [[meninges]], a system of [[membrane]]s that separate the skull from the brain.<ref name=CarpenterCh1 /> This three-layered covering is composed of (from the outside in) the [[dura mater]] ("hard mother"), [[arachnoid mater]] ("spidery mother"), and [[pia mater]] ("soft mother"). The arachnoid and pia are physically connected and thus often considered as a single layer, the pia-arachnoid. Below the arachnoid is the subarachnoid space which contains [[cerebrospinal fluid]] (CSF), which circulates in the narrow spaces between cells and through cavities called [[Ventricular system|ventricle]]s, and serves to nourish, support, and protect the brain tissue. [[Blood vessel]]s enter the central nervous system through the perivascular space above the pia mater. The cells in the blood vessel walls are joined tightly, forming the [[blood-brain barrier]] which protects the brain from [[toxin]]s that might enter through the blood.


Clapham Park was selected as a pilot site for [[New Deal for Communities]], which has brought some new education, training, health and community safety projects to the estate. Better management of Lambeth's housing has also alleviated some of the worst elements of physical disrepair of the estate. In 2005, tenants of the estate voted for a "stock transfer" to a [[housing association]], and ownership and management of their homes transferred from the London Borough of Lambeth to Clapham Park Homes, the new community led housing association, on 27 June 2006. The transfer is closely linked to ambitious and controversial plans for large scale redevelopment of the estate, which would increase the number of homes, substantially increase housing density and diversify tenure.
[[Image:Mouse brain.jpg|thumb|left|238px|A mouse brain.]]
The [[cortex]] is the part of the brain that most strongly distinguishes mammals from other vertebrates, primates from other mammals, and humans from other primates. In non-mammalian vertebrates, the surface of the cerebrum is lined with a comparatively simple layered structure called the [[pallium (anatomy)|pallium]].<ref>[[#refAboitiz|Aboitiz et al, 2003]]</ref> In mammals, the pallium evolves into a complex 6-layered structure called neocortex. In primates, the neocortex is greatly enlarged in comparison to its size in non-primates, especially the part called the [[frontal lobes]]. In humans, this enlargement of the frontal lobes is taken to an extreme, and other parts of the cortex also become quite large and complex.


'''Abbeville Village'''
===Principles of brain architecture===
[[Image:Human-leech-nervous-system-comparison.png|thumb|right|150px|Central nervous systems of a medical leech and a human, illustrating similarity of overall form.]]
The brain is the most complex biological structure known to us,<ref>[[#refShepherdNB|''Neurobiology'']], p 3</ref> and comparing the brains of different species on the basis of overt appearance is often difficult. Nevertheless there are common principles of brain architecture that apply across a very wide range of species. These are revealed mainly by three approaches: evolution, development, and genetics. The evolutionary approach means comparing brain structures of different species, and using the principle that features found in all branches that descend from a given ancient form were probably present in the ancestor as well. The developmental approach means examining how the form of the brain changes during the progression from embyronic to adult stages. The genetic approach means analyzing gene expression in various parts of the brain across a range of species. Each approach complements and informs the other two.


From the 1880s the area to the west of Cubitt's land holdings between [[Clapham Common]] Southside and the site of Lincoln House was developed to more conventional housing designs. This area borrowed the name of Clapham Park, presumably because of its original social cachet. These streets have predominantly remained in owner occupation. The grid of late [[Victorian era]] streets around Abbeville Road is frequently referred to (particularly by estate agents) as '''Abbeville Village''', although many independent local shops that gave the area a distinct character until the 1990s have made way for restaurants, cafes and bars, as the street has become the centre of local night life for the professional middle classes and shop rentals have increased exponentially.
[[Image:Bilaterian-plan.svg|thumb|left|300px|Body plan of a generic bilaterian animal. The nervous system has the form of a nerve cord with segmental enlargements, and a "brain" at the front.]]
With the exception of a few primitive forms such as sponges and jellyfish, all of the animals on earth today are [[bilateria]]ns, meaning animals with a bilaterally symmetric body shape (that is, left and right sides that are approximate mirror images of each other). Paleontologists believe that all bilaterians descend from a common ancestor that appeared early in the Cambrian period, 550-600 million years ago.<ref>[[#refUrbilateria|Balavoine & Adoutte, 2003]]</ref> This ancestor had the shape of a simple tube worm with a segmented body, and at an abstract level, that worm-shape continues to be reflected in the body and nervous system plans of all modern bilaterians, including humans.<ref>[[#refEvolutionOfOrganSystems|Evolution of Organ Systems]], p 110</ref> The fundamental bilaterian body form is a tube with a hollow gut cavity running from mouth to anus, and a nerve cord with an enlargement (a "ganglion") for each body segment, with an especially large ganglion at the front, called the "brain".

====Invertebrates====

In many invertebrates—insects, molluscs, worms of many types, etc.—the components of the brain, and their arrangement, differ so greatly from the vertebrate pattern that it is hard to make meaningful comparisons except on the basis of genetics. Two groups of invertebrates have notably complex brains: [[arthropod]]s ([[insect]]s, [[crustacean]]s, [[arachnid]]s, and others), and [[cephalopod]]s ([[octopus]]es, [[squid]]s, and similar [[mollusc]]s).<ref name="butler">[[#refButler|Butler, 2000]]</ref> The brains of arthropods and cephalopods arise from twin parallel nerve cords that extend through the body of the animal. Arthropods have a central brain with three divisions and large ''optical lobes'' behind each [[eye]] for visual processing.<ref name="butler"/>
Cephalopods have the largest brains of any invertebrates. The brain of the octopus in particular is highly developed, comparable in complexity to the brains of some vertebrates.

There are a few invertebrates whose brains have been studied intensively. The large sea slug [[aplysia]] was chosen by Nobel Prize-winning neurophysiologist [[Eric Kandel]], because of the simplicity and accessibility of its nervous system, as a model for studying the cellular basis of learning and memory, and subjected to hundreds of experiments.<ref>[[#refKandel|In Search of Memory]]</ref> The most thoroughly studied invertebrate brains, however, belong to the fruit fly [[drosophila]] and the tiny roundworm [[ Caenorhabditis elegans]].

[[Image:Drosophila melanogaster - side (aka).jpg|thumb|left|120px|''Drosophila'']]
Because of the large array of techniques available for studying their genetics, fruit flies have been a natural subject for studying the role of genes in brain development.<ref>[[#refFlybrain|Flybrain web site]]</ref> Remarkably, many aspects of ''drosophila'' neurogenetics have turned out to be relevant to humans. The first biological clock genes, for example, were identified by examining ''drosophila'' mutants that showed disrupted daily activity cycles.<ref>[[#refKonopka|Konopka & Benzer, 1971]]</ref> A search in the genomes of vertebrates turned up a set of analogous genes, which were found to play similar roles in the mouse biological clock—and therefore almost certainly in the human biological clock as well.<ref>[[#refShin|Shin et al, 1985]]</ref>

Like ''drosophila'', ''c. elegans'' has been studied largely because of its importance in genetics.<ref>[[#refWormbook|WormBook web site]]</ref> In the early 1970s, [[Sydney Brenner]] chose it as a [[model system]] for studying the way that genes control development. One of the advantages of working with this worm is that the body plan is very stereotyped: the nervous system of the [[hermaphrodite]] morph contains exactly 302 neurons, always in the same places, making identical synaptic connections in every worm.<ref>[[#refHobert|Hobert, ''WormBook'']]</ref> In a heroic project, Brenner's team sliced worms into thousands of ultrathin sections and photographed every section under an electron microscope, then visually matched fibers from section to section, in order to map out every neuron and synapse in the entire body.<ref>[[#refWhite|White et al, 1986]]</ref> Nothing approaching this level of detail is available for any other organism, and the information has been used to enable a multitude of studies that would not have been possible without it.

====Vertebrates====

[[Image:Shark brain.png|thumb|left|150px|The brain of a shark.]]
The first [[vertebrate]]s appeared over 500 million years ago (Mya), during the Cambrian period, and may have somewhat resembled the modern [[hagfish]] in form. Sharks appeared about 450 Mya, amphibians about 400 Mya, reptiles about 350 Mya, and mammals about 200 Mya. It is dangerous to describe any modern species as more "primitive" than others, since all have an equally long evolutionary history, but the brains of modern hagfishes, lampreys, sharks, amphibians, reptiles, and mammals show a gradient of size and complexity that roughly follows the evolutionary sequence.<ref>[[#refStriedter|''Principles of brain evolution'']]</ref> All of these brains contain the same set of basic anatomical components, but many are rudimentary in hagfishes, whereas in mammals the foremost parts are greatly elaborated and expanded.
[[Image:EmbryonicBrain.svg|thumb|right|238px|Diagram depicting the main subdivisions of the [[embryogenesis|embryonic]] vertebrate brain. These regions will later differentiate into forebrain, midbrain and hindbrain structures.]]
All vertebrate brains share a common underlying form, which can most easily be appreciated by examining how they develop.<ref>[[#refPrinciples|''Principles of Neural Science'']], p 1019</ref> The first appearance of the nervous system is as a thin strip of tissue running along the back of the embryo. This strip thickens and then folds up to form a hollow tube. The front end of the tube develops into the brain. In its earliest form, the brain appears as three swellings, which eventually become the forebrain, midbrain, and hindbrain. In many classes of vertebrates these three parts remain similar in size in the adult, but in mammals the forebrain becomes much larger than the other parts, and the midbrain quite small.

[[Image:Vertebrate-brain-regions.png|thumb|left|200px|Main anatomical regions of the vertebrate brain.]]
Neuroanatomists usually consider the brain to consist of six main regions: the telencephalon (cerebral hemispheres), diencephalon (thalamus and hypothalamus), mesencephalon (midbrain), cerebellum, pons, and medulla.<ref>[[#refPrinciples|Principles of Neural Science]], Ch. 17</ref> Each of these areas in turn has a complex internal structure. Some areas, such as the cortex and cerebellum, consist of layers, folded or convoluted to fit within the available space. Other areas consist of clusters of many small nuclei. If fine distinctions are made on the basis of neural structure, chemistry, and connectivity, thousands of distinguishable areas can be identified within the vertebrate brain.

Some branches of vertebrate evolution have led to substantial changes in brain shape, especially in the forebrain. The brain of a shark shows the basic components in a straighforward way, but in [[teleost]] fishes (the great majority of modern species), the forebrain has become "everted", like a sock turned inside out. In birds, also, there are major changes in shape.<ref>[[#refNorthcutt2008|Northcutt, 2008]]</ref> One of the main structures in the avian forebrain, the [[dorsal ventricular ridge]], was long thought to correspond to the basal ganglia of mammals, but is now thought to be more closely related to the neocortex.<ref>[[#refReiner|Reiner et al, 2005]]</ref>

[[Image:Vertebrate-brain-cartoon.png|thumb|right|400px|Crude sketch of the approximate locations of several important parts of the vertebrate brain, on the outline of a shark brain.]]
=====Areas of the vertebrate brain and their functions=====
Several brain areas have maintained their identities across the whole range of vertebrates, from hagfishes to humans. Here is a list of some of the most important areas, along with a very brief description of their functions as currently understood (but note that the functions of most of them are still disputed to some degree):
*The [[medulla]], along with the spinal cord, contains many small nuclei involved in a wide variety of sensory and motor functions.
*The [[hypothalamus]] is a small region at the base of the forebrain, whose complexity and importance belies its size. It is composed of numerous small nuclei, each with distinct connections and distinct neurochemistry. The hypothalamus is the central control station for sleep/wake cycles, control of eating and drinking, control of hormone release, and many other critical biological functions.<ref>[[#refSwaab|Swaab et al, ''The human hypothalamus'']]</ref>
*Like the hypothalamus, the [[thalamus]] is a collection of nuclei with diverse functions. Some of them are involved in relaying information to and from the cerebral hemispheres. Others are are involved in motivation. The subthalamic area (zona incerta) seems to contain action-generating systems for several types of "consummatory" behaviors, including eating, drinking, defecation, and copulation.<ref>[[#refThalamus|Jones, ''The thalamus'']]</ref>
*The [[cerebellum]] modulates the outputs of other brain systems to make them more precise. Removal of the cerebellum does not prevent an animal from doing anything in particular, but it makes actions hesitant and clumsy. This precision is not built-in, but learned by trial and error. Learning how to ride a bicycle is an example of a type of neural plasticity that may take place largely within the cerebellum.<ref>[[#refPrinciples|''Principles of Neural Science'']], Ch. 42</ref>
*The [[tectum]], often called "optic tectum", allows actions to be directed toward points in space. In mammals it is called the "superior colliculus", and its best studied function is to direct eye movements. It also directs reaching movements, though. It gets strong visual inputs, but also inputs from other senses that are useful in directing actions, such as auditory input in owls, input from the thermosensitive pit organs in snakes, etc. In some fishes, it is the largest part of the brain.<ref>[[#refSaitoh|Saitoh et al, 2007]]</ref>
*The [[pallium]] is a layer of gray matter that lies on the surface of the forebrain. In reptiles and mammals it is called [[cortex]] instead. The pallium is involved in multiple functions, including olfaction and spatial memory. In mammals, where it comes it dominate the brain, it subsumes functions from many subcortical areas.<ref>[[#refPuelles|Puelles, 2001]]</ref>
*The [[hippocampus]], strictly speaking, is found only in mammals. However, the area it derives from, the medial pallium, has counterparts in all vertebrates. There is evidence that this part of the brain is involved in spatial memory and navigation in fishes, birds, reptiles, and mammals.<ref>[[#refSalas|Salas et al, 2003]]</ref>
*The [[basal ganglia]] are a group of interconnected structures in the forebrain, of which our understanding has increased enormously over the last few years. The primary function of the basal ganglia seems to be [[action selection]]. They send inhibitory signals to all parts of the brain that can generate actions, and in the right circumstances can release the inhbition, so that the action-generating systems are able to execute their actions. Rewards and punishments exert their most important neural effects within the basal ganglia.<ref>[[#refGrillner2005|Grillner et al, 2005]]</ref>
*The [[olfactory bulb]] is a special structure that processes olfactory sensory signals, and sends its output to the olfactory part of the pallium. It is a major brain component in many vertebrates, but much reduced in primates.<ref>[[#refNorthcutt1981|Northcutt, 1981]]</ref>

====Mammals====
[[Image:Cerebral-evolution.png|thumb|right|160px|Increase in relative size of the cerebral hemispheres (shaded) in the evolutionary progression leading to primates.]]
The hindbrain and midbrain of mammals are generally similar to those of other vertebrates, but dramatic differences appear in the forebrain, which is not only greatly enlarged, but also altered in structure.<ref>[[#refBarton|Barton & Harvey, 2000]]</ref> In mammals, the surface of the cerebral hemispheres is mostly covered with 6-layered ''isocortex'', more complex than the 3-layered [[pallium]] seen in most vertebrates. Also the [[hippocampus]] of mammals has a distinctive structure.

Unfortunately, the evolutionary history of these mammalian features, especially the 6-layered cortex, is difficult to work out.<ref>[[#refAboitiz|Aboitiz, 2004]]</ref> This is largely because of a "missing link" problem. The ancestors of mammals, called [[synapsid]]s, split off from the ancestors of modern reptiles and birds about 350 million years ago. However, the most recent branching that has left living results within the mammals was the split between [[monotreme]]s (the platypus and echidna), [[marsupial]]s (opossum, kangaroo, etc.) and [[placental]]s (most living mammals), which took place about 120 million years ago. The brains of monotremes and marsupials are distinctive from those of placentals in some ways, but they have fully mammalian cortical and hippocampal structures. Thus, these structures must have evolved between 350 and 120 million years ago, a period that has left no evidence except fossils, which do not preserve tissue as soft as brain.

====Primates, including humans====
{{main|Human brain}}

The primate brain contains the same structures as the brains of other mammals, but is considerably larger in proportion to body size.<ref name="Finlay" /> Most of the enlargement comes from a massive expansion of the cortex, focusing especially on the parts subserving vision and forethought.<ref>[[#refCalvin1996|Calvin, ''How brains think'']]</ref> The visual processing network of primates is very complex, including at least 30 distinguishable areas, with a bewildering web of interconnections. Taking all of these together, visual processing makes use of about half of the brain. The other part of the brain that is greatly enlarged is the [[prefrontal cortex]], whose functions are difficult to summarize succinctly, but relate to planning, working memory, motivation, attention, and executive control.

===Brain size and its significance===
<!--this section really begs for an illustration showing a data-plot -->

There has been quite a bit of study of the relationships between brain size, body size, and other variables across a wide range of species, largely because the easiest way to study any object is to measure its size. Even for extinct species brain size can be estimated by measuring the cavity inside the skull. The story that emerges, however, is complex.

As might be expected, brain size tends to increase with body size (measured by weight, which is roughly equivalent to volume). The relationship is not a strict proportionality, though: averaging across all orders of mammals, it follows a power law, with an exponent of about 0.75.<ref>[[#refArmstrong|Armstrong, 1983]]</ref> There are good reasons for expecting a power law: for example, the body-size-to-body-length relationship follows a power law with an exponent of 0.33, and the body-size-to-surface-area relationship a power law with an exponent of 0.67. The explanation for an exponent of 0.75 is not obvious, though—however it is worth noting that several physiological variables appear to be related to body size by approximately the same exponent, for example, the basal metabolic rate.<ref>[[#refSavage|Savage et al, 2004]]</ref> This power law formula applies to the "average" brain of mammals taken as a whole, but each family (cats, rodents, primates, etc) departs from it to some degree, in a way that generally reflects the overall "sophistication" of behavior.<ref>[[#refJerison|Jerison, 1973]]</ref> Primates, for a given body size, have brains 5 to 10 times as large as the formula predicts. Predators tend to have relatively larger brains than the animals they prey on; placental mammals (the great majority) have relatively larger brains than marsupials such as the opossum.

When the mammalian brain increases in size, not all parts increase at the same rate.<ref name="Finlay">[[#refFinlay|Finlay et al, 2001]]</ref> In particular, the larger the brain of a species, the greater the fraction taken up by the cortex. Thus, in the species with the largest brains, most of their volume is filled with cortex: this applies not only to humans, but also to animals such as dolphins, whales, or elephants.

The evolution of ''homo sapiens'' over the past two million years has been marked by a steady increase in brain size, but much of it can be accounted for by corresponding increases in body size.<ref>[[#refKappelman|Kappelman, 1993]]</ref> There are, however, many departures from the trend that are difficult to explain in a systematic way: in particular, the appearance of modern man about 100,000 years ago was marked by a decrease in body size at the same time as an increase in brain size. Even so, it is notorious that Neanderthals, which went extinct about 40,000 years ago, had larger brains than modern ''homo sapiens''.<ref>[[#refHolloway|Holloway, 1995]]</ref>

Not all investigators are happy with the amount of attention that has been paid to brain size. Roth and Dicke, for example, have argued that factors other than size are more highly correlated with intelligence, such as the number of cortical neurons and the speed of their connections.<ref>[[#refRoth|Roth & Dicke, 2005]]</ref> Moreover they point out that intelligence depends not just on the amount of brain tissue, but on the details of how it is structured.

===Microscopic structure===
{{Neuron map|[[Neuron]]}}
The brain is composed of two broad classes of cells, [[neuron]]s and [[glia]].<ref>[[#refPrinciples|''Principles of neural science'']] p 20</ref> Neurons receive more attention, but glial cells actually outnumber them by at least 10 to 1. Glia come in several types, which perform a number of critical functions, including structural support, metabolic support, insulation, and guidance of development.

The property that makes neurons so important is that, unlike glia, they are capable of sending signals to each other over long distances.<ref>[[#refPrinciples|''Principles of neural science'']], p 21</ref> They send these signals by means of an [[axon]], a thin protoplasmic fiber that extends from the cell body and projects, usually with numerous branches, to other areas, sometimes nearby, sometimes in distant parts of the brain or body. The extent of an axon can be extraordinary: to take an example, if a pyramidal cell of the neocortex were magnified so that its cell body became the size of a human, its axon, equally magnified, would become a cable a few inches in diameter, extending farther than a mile. These axons transmit signals in the form of electrochemical pulses called [[action potentials]], lasting less than a thousandth of a second and traveling along the axon at speeds of 1-100 meters per second. Some neurons emit action potentials constantly, at rates of 10-100 per second, usually in irregular temporal patterns; other neurons are quiet most of the time, but occasionally emit a burst of action potentials.

[[Image:Chlorocebus-nissl-brainmaps.png|thumb|right|200px|Nissl-stained cross section of Chlorocebus monkey brain. Source: ''brainmaps.org'']]
Axons transmit signals to other neurons, or to non-neuronal cells, by means of specialized junctions called [[synapse]]s.<ref>[[#refPrinciples|''Principles of neural science'']], Ch. 10</ref> A single axon may make as many as several thousand synaptic connections. When an action potential, traveling along an axon, arrives at a synapse, it causes a chemical called a [[neurotransmitter]] to be released. The neurotransmitter binds to [[chemical receptor|receptor]] molecules in the membrane of the target cell. Some types of neuronal receptors are ''excitatory'', meaning that they increase the rate of action potentials in the target cell; other receptors are ''inhibitory'', meaning that they decrease the rate of action potentials; others have complex modulatory effects on the target cell.

Axons actually fill most of the space in the brain.<ref>[[#refPrinciples|''Principles of neural science'']], Ch. 2</ref> Often large groups of them travel together in bundles called "nerve fiber tracts". In many cases, each axon is wrapped in a thick sheath of a fatty substance called [[myelin]], which serves to greatly increase the speed of action potential propagation. Myelin is white in color, so parts of the brain filled exclusively with nerve fibers appear as "white matter", in contrast to the "gray matter" that marks areas where high densities of neuron cell bodies are located. The illustration on the right shows a thin section of one hemisphere of the brain of a Chlorocebus monkey, stained using a [[Nissl stain]], which colors the cell bodies of neurons.<ref>[[#refPrinciples|''Principles of neural science'']], p 326</ref> This makes the gray matter show up as a dark blue, and the white matter show up as a paler blue. Several important forebrain structures, including the cortex, can easily be identified in brain sections that are stained in this way. Neuroanatomists have invented hundreds of stains that color different types of neurons, or different types of brain tissue, in distinct ways: the Nissl stain shown here is probably the most widely used.

===Development===

The brain does not simply grow; it develops in an intricately orchestrated sequence of steps.<ref>[[#refPurvesLichtman|''Principles of Neural Development'']], Ch. 1</ref> Many neurons are created in special zones that contain [[stem cells]], and then migrate through the tissue to reach their ultimate locations.<ref>[[#refPurvesLichtman|''Principles of Neural Development'']], Ch. 4</ref> In the cortex, for example, the first stage of development is the formation of a "scaffold" by a special group of glial cells, called [[radial glia]], which send fibers vertically across the cortex. New cortical neurons are created at the bottom of the cortex, and then "climb" along the radial fibers until they reach the layers they are destined to occupy in the adult.

Once a neuron is in place, it begins to extend dendrites and an axon into the area around it.<ref>[[#refPurvesLichtman|''Principles of Neural Development'']], Chs. 5, 7</ref> Axons, because they commonly extend a great distance from the cell body and need to make contact with specific targets, grow in a particularly complex way. The tip of a growing axon consists of a blob of protoplasm called a "growth cone", studded with chemical receptors. These receptors sense the local environment, causing the growth cone to be attracted or repelled by various cellular elements, and thus to be pulled in a particular direction at each point along its path. The result of this pathfinding process is that the growth cone navigates through the brain until it reaches its destination area, where other chemical cues cause it to begin generating synapses. Taking the entire brain into account, many thousands of genes give rise to proteins that influence axonal pathfinding.

The synaptic network that finally emerges is only partly determined by genes, though. In many parts of the brain, axons initially "overgrow", and then are "pruned" by mechanisms that depend on neural activity.<ref>[[#refPurvesLichtman|''Principles of Neural Development'']], Ch. 12</ref> In the projection from the eye to the midbrain, for example, the structure in the adult contains a very precise mapping, connecting each point on the surface of the [[retina]] to a corresponding point in a midbrain layer. In the first stages of development, each axon from the retina is guided to the right general vicinity in the midbrain by chemical cues, but then branches very profusely and makes initial contact with a wide swath of midbrain neurons. The retina, before birth, contains special mechanisms that cause it to generate waves of activity that originate spontaneously at some point and then propagate slowly across the retinal layer.<ref>[[#refWong|Wong, 1999]]</ref> These waves are useful because they cause neighboring neurons to be active at the same time: that is, they produce a neural activity pattern that contains information about the spatial arrangement of the neurons. This information is exploited in the midbrain by a mechanism that causes synapses to weaken, and eventually vanish, if activity in an axon is not followed by activity of the target cell. The result of this sophisticated process is a gradual tuning and tightening of the map, leaving it finally in its precise adult form.

Similar things happen in other brain areas: an initial synaptic matrix is generated as a result of genetically determined chemical guidance, but then gradually refined by activity-dependent mechanisms, partly driven by internal dynamics, partly by external sensory inputs. In some cases, as with the retina-midbrain system, activity patterns depend on mechanism that operate only in the developing brain, and apparently exist solely for the purpose of guiding development.

In humans, and many other mammals, new neurons are created mainly before birth. In humans, the infant brain actually contains substantially more neurons than the adult brain.<ref>[[#refPurvesLichtman|''Principles of Neural Development'']], Ch. 6</ref> There are, however, a few areas where new neurons continue to be generated throughout life. The two areas for which this is well established are the olfactory bulb, which is involved in the sense of smell, and the dentate gyrus of the [[hippocampus]], where there is evidence that the new neurons play a role in storing newly acquired memories. With these exceptions, however, the set of neurons that are present in early childhood is the set that are present for life. (Glial cells are different: as with most types of cells in the body, these are generated throughout the lifespan.)

Although the pool of neurons is largely in place by birth, their axonal connections continue to develop for years afterward. In particular, in humans full myelination is not completed until the age of 5 or 6.

====Nature versus nurture====
{{main|Nature versus nurture}}

There has long been debate about whether the qualities of mind, personality, and intelligence can mainly be attributed to heredity or to upbringing.<ref>[[#refRidley|Ridley, ''Nature vs Nurture'']]</ref> This is not just a philosophical question: it has great practical relevance to parents and educators. Although many details remain to be settled, neuroscience clearly shows that both factors are essential. Genes determine the general form of the brain, and genes determine how the brain reacts to experience. Experience, however, is required to refine the matrix of synaptic connections. In some respects it is mainly a matter of presence or absence of experience during critical periods of development.<ref>[[#refWiesel|Wiesel, 1982]]</ref> In other respects, the quantity and quality of experience may be more relevant: for example, there is substantial evidence that animals raised in enriched environments have thicker cortices (indicating a higher density of synaptic connections) than animals whose levels of stimulation are restricted.<ref>[[#refvanPraag|van Praag et al, 2000]]</ref>

==Functions of the brain==

Vertebrate brains receive signals through nerves arriving from sensory systems. These signals are then processed throughout the central nervous system; reactions are formulated based upon reflex and learned experiences. A similarly extensive nerve network delivers signals from the brain to muscles throughout the body. Anatomically, the majority of afferent (incoming) and efferent (outgoing) nerves are connected to the spinal cord, which then transfers the signals to and from the brain. There are also, however, several [[cranial nerves]] that connect parts of the body directly to the brain.

Sensory input is processed by the brain to recognize danger, find food, identify potential mates, and perform more sophisticated functions. [[Visual perception|Visual]], touch, and [[hearing (sense)|auditory]] sensory pathways of vertebrates are routed to specific nuclei of the [[thalamus]] and then to regions of the cerebral cortex that are specific to each [[sensory system]], the [[visual system]], the [[auditory system]], and the [[somatosensory system]]. Olfactory pathways are routed to the olfactory bulb, then to various parts of the [[olfactory system]]. [[Taste]] is routed through the brainstem and then to other portions of the [[gustatory system]].

To control movement the brain has several parallel systems of muscle control. The motor system controls voluntary muscle movement, aided by the [[motor cortex]], [[cerebellum]], and the [[basal ganglia]]. The system eventually projects to the spinal cord and then out to the muscle effectors. Nuclei in the brain stem control many involuntary muscle functions such as heart rate and breathing. In addition, many automatic acts (simple reflexes, locomotion) can be controlled by the spinal cord alone.


===Brain systems===

The brain can be divided into subsystems in a number of ways: anatomically (as described above), chemically, and functionally.

====Neurotransmitter systems====
{{Main|Neurotransmitter systems}}
With few exceptions, each neuron in the brain releases the same [[neurotransmitter]], or set of neurotransmitters, at all of the synaptic connections it makes with other neurons.<ref>See [[Dale's principle]]</ref> Thus, a neuron can be characterized by the neurotransmitters it releases. The two neurotransmitters that appear most frequently are [[glutamate]] (which is almost always excitatory), and [[GABA]] (which is almost always inhibitory). Neurons using these transmitters can be found in nearly every part of the brain. In fact, they combine numerically to make up more than 99% of the brain's entire pool of synapses.

This does not mean that other neurotransmitters are unimportant, though. The great majority of psychoactive drugs exert their effects by altering neurotransmitter systems, and only a small proportion of them act directly on glutamatergic or GABAergic transmission. Drugs such as caffeine, nicotine, heroin, cocaine, Prozac, Thorazine, etc., etc. act on other neurotransmitters. Many of these other transmitters come from neurons that are localized in particular parts of the brain. [[Serotonin]], for example—the primary target of antidepressant drugs and many dietary aids—comes exclusively from a small brainstem area called the [[Raphe nuclei]]. [[Norepinephrine]], which is involved in arousal, comes exclusively from a nearby small area called the [[locus ceruleus]]. Histamine, as a neurotransmitter, comes from a tiny part of the hypothalamus called the tuberomammilary nucleus (histamine also has non-CNS functions, but the neurotransmitter function is what causes antihistamines to have sedative effects). Other neurotransmitters such as [[acetylcholine]] and [[dopamine]] have multiple sources in the brain, but are not as ubiquitously distributed as glutamate and GABA.

====Sensory systems====
{{Main|Sensory system}}

One of the primary functions of a brain is to extract biologically relevant information from sensory inputs. Even in the human brain, sensory processes go well beyond the classical five senses of sight, sound, taste, touch, and smell: our brains are provided with information about temperature, balance, limb position, and the chemical composition of the bloodstream, among other things. All of these modalities are detected by specialized sensors that project signals into the brain. In non-humans, additional senses may be present, such as the infrared heat-sensors in the pit organs of snakes; or the "standard" senses may be used in nonstandard ways, as in the auditory "sonar" of bats.

Every sensory system has idiosyncrasies, but here is a list of a few general principles, using the sense of hearing for examples:
#Each system begins with specialized "sensory receptor" cells. These are neurons, but unlike most neurons, they are not controlled by synaptic input from other neurons: instead they are activated by membrane-bound receptors that are sensitive to some physical modality, such as light, temperature, or physical stretching. The axons of sensory receptor cells travel into the spinal cord or brain. For the sense of hearing, the receptors are located in the inner ear, on the cochlea, and are activated by vibration.
#For most senses, there is a "primary nucleus" or set of nuclei, located in the brainstem, that gathers signals from the sensory receptor cells. For the sense of hearing, these are the [[cochlear nuclei]].
#In many cases, there are secondary subcortical areas that extra special information of some sort. For the sense of hearing, the superior olivary area and inferior colliculus are involved in comparing the signals from the two ears to extract information about the direction of the sound source, among other functions.
#Each sensory system also has a special part of the [[thalamus]] dedicated to it, which serves as a relay to the cortex. For the sense of hearing, this is the [[medial geniculate nucleus]].
#For each sensory system, there is a "primary" cortical area that receives direct input from the thalamic relay area. For the auditory system this is A1, located in the upper part of the temporal lobe.
#There are also usually a set of "higher level" cortical sensory areas, which analyze the sensory input in specific ways. For the auditory system, there are areas that analyze sound quality, rhythm, and temporal patterns of change, among other features.
#Finally, there are ''multimodal'' areas that combine inputs from different sensory modalities, for example auditory and visual. At this point, the signals have reached parts of the brain that are best described as ''integrative'' rather than specifically ''sensory''.

All of these rules have exceptions, for example: (1) For the sense of touch (which is actually a set of at least half-a-dozen distinct mechanical senses), the sensory inputs terminate mainly in the spinal cord, on neurons that then project to the brainstem. (2) For the sense of smell, there is no relay in the thalamus; instead the signals go directly from the primary brain area—the olfactory bulb—to the cortex.

====Motor systems====

Motor systems are areas of the brain that are more or less directly involved in producing body movements, that is, in activating muscles. With the exception of the muscles that control the eye, all of the "voluntary" muscles<ref>See [[muscle]]</ref> in the body are directly innervated by [[motor neuron]]s in the spinal cord, which therefore are the "final common path" for the movement-generating system. Spinal motor neurons are controlled both by neural circuits intrinsic to the spinal cord, and by inputs that descend from the brain. The intrinsic spinal circuits implement many [[reflex]] responses, and also contain [[central pattern generator|pattern generators]] for rhythmic movements such as walking or swimming. The descending connections from the brain allow for more sophisticated control.

The brain contains a number of areas that project directly to the spinal cord. At the lowest level are motor areas in the medulla and pons. At a higher level are areas in the midbrain, such as the [[red nucleus]], which is responsible for coordinating movements of the arms and legs. At a higher level yet is the [[primary motor cortex]], a strip of tissue located at the posterior edge of the frontal lobe. The primary motor cortex sends projections to the subcortical motor areas, but also sends a massive projection directly to the spinal cord, via the so-called [[pyramidal tract]]. This direct corticospinal projection allows for precise voluntary control of the fine details of movements.

Other "secondary" motor-related brain areas do not project directly to the spinal cord, but instead act on the cortical or subcortical primary motor areas. Among the most important secondary areas are the premotor cortex, basal ganglia, and cerebellum:
*The [[premotor cortex]] (which is actually a large complex of areas) adjoins the primary motor cortex, and projects to it. Whereas elements of the primary motor cortex map to specific body areas, elements of the premotor cortex are often involved in coordinated movements of multiple body parts.
*The [[basal ganglia]] are a set of structures in the base of the forebrain that project to many other motor-related areas. Their function has been difficult to understand, but the most popular theory currently is that they play a key role in [[action selection]]. Most of the time they restrain actions by sending constant inhibitory signals to action-generating systems, but in the right circumstances, they release this inhibition and therefore allow their targets to take control of behavior.
* The [[cerebellum]] is a very distinctive structure attached to the back of the brain. It does not control or originate behaviors, but instead generates corrective signals to make movements more precise. People with cerebellar damage are not paralyzed in any way, but their body movements become erratic and uncoordinated.

In addition to all of the above, the brain and spinal cord contain extensive circuitry to control the [[autonomic nervous system]], which works by secreting hormones and by modulating the "smooth" muscles of the gut. The autonomic nervous system affects heart rate, digestion, respiration rate, salivation, perspiration, urination, and sexual arousal—but most of its functions are not under direct voluntary control.

==== Arousal systems ====

{{main|sleep}}
Perhaps the most obvious aspect of the behavior of any animal is the daily cycle between sleeping and waking. Arousal and alertness are also modulated on a finer time scale, though, by an extensive network of brain areas.

A key component of the arousal system is the [[suprachiasmatic nucleus]] (SCN), a tiny part of the hypothalamus located directly above the point at which the optic nerves from the two eyes cross. The SCN contains the body's central biological clock. Neurons there show activity levels that rise and fall with a period of about 24 hours: these activity fluctuations are driven by rhythmic changes in expression of a set of "clock genes". The SCN continues to keep time even if it is excised from the brain and placed in a dish of warm nutrient solution, but it ordinarily receives input from the optic nerves that allow daily light-dark cycles to calibrate the clock.

The SCN projects to a set of areas in the hypothalamus, brainstem, and midbrain that are involved in implementing sleep-wake cycles. An important component of the system is the so-called [[reticular formation]], a group of neuron-clusters scattered diffusely through the core of the lower brain. Reticular neurons send signals to the thalamus, which in turn sends activity-level-controlling signals to every part of the cortex. Damage to the reticular formation can produce a permanent state of coma.

[[Sleep]] involves great changes in brain activity. Until the 1950s it was generally believed that the brain essentially shuts off during sleep, but this is now known to be far from true: activity continues, but the pattern becomes very different. In fact, there are two types of sleep, ''slow wave sleep'' (non-dreaming) and ''REM sleep'' (dreaming), each with its own distinct brain activity pattern. During slow wave sleep, activity in the cortex takes the form of large synchronized waves, where in the waking state it is noisy and desynchronized. Levels of the neurotransmitters [[norepinephrine]] and [[serotonin]] drop during slow wave sleep, and fall almost to zero during REM sleep; levels of [[acetylcholine]] show the reverse pattern.

[[Image:PET-image.jpg|thumb|right|150px|[[Positron emission tomography|PET]] Image of the human brain showing energy consumption]]
===Brain energy consumption===
Although the brain represents only 2% of the body weight, it receives 15% of the cardiac output, 20% of total body oxygen consumption, and 25% of total body glucose utilization.<ref>[[#refClark|Clark & Sokoloff, 1999]]</ref> The demands of the brain limit its size in some species, such as bats.<ref>[[#refSafi|Safi et al, 2005]]</ref> The brain mostly utilizes glucose for energy, and deprivation of glucose, as can happen in hypoglycemia, can result in loss of consciousness. The energy consumption of the brain does not vary greatly over time, but active regions of the cortex consume somewhat more energy than inactive regions: this fact forms the basis for the functional brain imaging methods [[Positron emission tomography|PET]] and [[fMRI]].<ref>[[#refRaichle|Raichle & Gusnard, 2002]]</ref>

==Effects of damage and disease==

{{main|Neurology}}

Even though it is protected by the skull and [[meninges]], surrounded by [[cerebrospinal fluid]], and isolated from the bloodstream by the [[blood-brain barrier]], the delicate nature of the brain makes it vulnerable to numerous diseases and several types of damage. Because these problems generally manifest themselves differently in humans than in other species, an overview of brain pathology and how it can be treated is deferred to the [[Human brain]], [[Brain damage]], and [[Neurology]] articles.

==Brain and mind==
{{main|Philosophies of mind}}
{{portalpar|Mind and Brain}}

It is not easy to understand the relationship between the physical brain and something as ethereal as the mind. It is hard to doubt that a relationship of some sort exists: the clearest evidence is that numerous drugs, which obviously act directly on the physical substance of the brain, have strong effects on the mind. But what is the upshot? Does this mean that the brain ''is'' the mind? Or only that they are bound together in some intimate way? Many people have had a strong intuition, or at least a strong wish to believe, that the mind is fundamentally a separate thing, with an independent existence, capable perhaps of detaching from the body and surviving even after death.

Through most of history the great majority of people, including philosophers, found it inconceivable that anything like ''thought'' could be implemented by what is in essence a mere piece of meat. Even Descartes, with his mechanistic philosophy, could not imagine how this could be. He had no problem explaining reflexes and other simple behaviors in mechanistic terms, but he could not believe that complex thought—and ''language'' in particular—could be explained in the same way. The invention of computers has made a great difference here. We can now see all around us machines capable of processing language in sophisticated ways—not with the full sophistication of a human mind, but nevertheless in ways that earlier generations could not guess at. Nevertheless, some philosophers continue to argue that there are properties of the human mind that cannot, ''in principle'', be explained mechanistically.

This problem—the [[mind-body problem]]—is one of the central issues in the history of [[philosophy]]. The brain is the physical and biological [[matter]] contained within the [[skull]], responsible for electrochemical neuronal processes while the mind consists of mental attributes, like [[belief]]s, desires, and [[perception]]s. There are scientifically demonstrable correlations between mental events and neuronal events; the philosophical question is whether these phenomena are identical, at least partially distinct, or related in some unknown way.
There are three major schools of thought concerning the answer: dualism, materialism, and idealism. [[Dualism (philosophy of mind)|Dualism]] holds that the mind exists independently of the brain;<ref>[[#refHart|Hart, 1996]]</ref> [[materialism]] holds that mental phenomena are identical to neuronal phenomena;<ref name="DicPhil">[[#refLacey|Lacey, 1996]]</ref> and [[idealism (philosophy)|idealism]] holds that only mental substances and phenomena exist.<ref name="DicPhil"/>

In addition to the philosophical questions, the relationship between mind and brain involves a number of scientific questions. What is the detailed relationship between thought and brain activity? What are the mechanisms by which drugs influence thought? What is [[consciousness]], in physical terms, and what are the [[neural correlates of consciousness]]? These questions fall into the domain of [[cognitive neuroscience]].

==How the brain is studied==
===Fields of study===
[[Neuroscience]] seeks to understand the nervous system, including the brain, from a biological and [[computational neuroscience|computational]] perspective. [[Psychology]] seeks to understand behavior and the brain. [[Neurology]] refers to the [[medicine|medical]] applications of neuroscience. The brain is also one of the most important organs studied in [[psychiatry]], the branch of medicine which exists to study, prevent, and treat [[mental disorders]].<ref name=Storrow1>Storrow, H.A. (1969). ''Outline of Clinical Psychiatry''. New York: Appleton-Century-Crofts, p. 1. ISBN 978-0-39-085075-1</ref><ref name=Lyness3>Lyness, J.M. (1997). ''Psychiatric Pearls''. Philadelphia: F.A. Davis Company, p. 3. ISBN 978-0-80-360280-9</ref><ref name=Guze4>Guze, S.B. (1992). ''Why Psychiatry Is a Branch of Medicine''. New York: Oxford University Press, p. 4. ISBN 978-0-19-507420-8</ref> [[Cognitive science]] seeks to unify neuroscience and psychology with other fields that concern themselves with the brain, such as [[computer science]] ([[artificial intelligence]] and similar fields) and [[philosophy]].

===Methods of observation===
{{main|neuroimaging}}
Each method for observing activity in the brain has its advantages and drawbacks.

====Electrophysiology====
Electrophysiology allows scientists to record the electrical activity of individual neurons or groups of neurons.

====EEG====
By placing electrodes on the scalp one can record the summed electrical activity of the cortex in a technique known as [[electroencephalography]] (EEG). EEG measures the mass changes in electrical current from the cerebral cortex, but can only detect changes over large areas of the brain with very little sub-cortical activity.

====MEG====
Apart from measuring the electric field around the skull it is possible to measure the magnetic field directly in a technique known as [[magnetoencephalography]] (MEG). This technique has the same temporal resolution as EEG but much better spatial resolution, although admittedly not as good as fMRI. The main advantage over fMRI is a direct relationship between neural activation and measurement.

====fMRI and PET====
[[Image:FMRI.jpg|thumb|238px|A scan of the brain using fMRI]]
Functional magnetic resonance imaging (fMRI) measures changes in [[blood flow]] in the brain, but the activity of neurons is not directly measured, nor can it be distinguished whether this activity is inhibitory or excitatory. fMRI is a noninvasive, indirect method for measuring neural activity that is based on '''BOLD'''; '''B'''lood '''O'''xygen '''L'''evel '''D'''ependent changes. The changes in blood flow that occur in capillary beds in specific regions of the brain are thought to represent various neuronal activities ([[metabolism]] of synaptic reuptake). Similarly, a [[Positron emission tomography| positron emission tomography]] (PET), is able to monitor [[glucose]] and [[oxygen]] metabolism as well as neurotransmitter activity in different areas within the brain which can be correlated to the level of activity in that region.

====Behavioral====
Behavioral tests can measure symptoms of disease and mental performance, but can only provide indirect measurements of brain function and may not be practical in all animals. In humans however, a neurological exam can be done to determine the location of any trauma, [[lesion]], or [[tumor]] within the brain, brain stem, or spinal cord.

====Anatomical====
[[post-mortem|Autopsy]] analysis of the brain allows for the study of anatomy and [[protein]] expression patterns, but is only possible after the human or animal is dead. [[Magnetic resonance imaging]] (MRI) can be used to study the anatomy of a living creature and is widely used in both research and medicine.

===Other studies===
[[computer science|Computer scientists]] have produced simulated "[[artificial neural network]]s" loosely based on the structure of neuron connections in the brain. Some [[artificial intelligence]] research seeks to replicate brain function—although not necessarily brain mechanisms—but as yet has been met with only limited success.

Creating [[algorithm]]s to mimic a biological brain is very difficult because the brain is not a static arrangement of circuits, but a network of vastly interconnected neurons that are constantly changing their connectivity and sensitivity. More recent work in both neuroscience and artificial intelligence models the brain using the [[mathematics|mathematical]] tools of [[chaos theory]] and [[dynamical system]]s. Current research has also focused on recreating the neural structure of the brain with the aim of producing human-like cognition and artificial intelligence.

==History of understanding of the brain==

{{main|History of the brain}}
Early views were divided as to whether the seat of the soul lies in the brain or heart. On one hand, it was impossible to miss the fact that awareness feels like it is localized in the head, and that blows to the head can cause unconsciousness much more easily than blows to the chest, and that shaking the head causes dizziness. On the other hand, the brain to a superficial examination seems inert, whereas the heart is constantly beating. Cessation of the heartbeat means death; strong emotions produce changes in the heartbeat; and emotional distress often produces a sensation of pain in the region of the heart ("heartache"). Aristotle favored the heart, and thought that the function of the brain is merely to cool the blood. Democritus, the inventor of the atomic theory of matter, favored a three-part soul, with intellect in the head, emotion in the heart, and lust in the vicinity of the liver.<ref>[[#refFinger|''History of Neuroscience'']], p 14</ref> Hippocrates, the "father of medicine", was entirely in favor of the brain. In ''On the Sacred Disease'', his account of epilepsy, he wrote:

{{cquote|Men ought to know that from nothing else but the brain come joys, delights, laughter and sports, and sorrows, griefs, despondency, and lamentations. ... And by the same organ we become mad and delirious, and fears and terrors assail us, some by night, and some by day, and dreams and untimely wanderings, and cares that are not suitable, and ignorance of present circumstances, desuetude, and unskilfulness. All these things we endure from the brain, when it is not healthy…|20px|20px|Hippocrates|<ref>[[#refHippocrates|On the Sacred Disease]]</ref>}}

The famous Roman physician Galen also advocated the importance of the brain, and theorized in some depth about how it might work. Even after physicians and philosophers had accepted the primacy of the brain, though, the idea of the heart as seat of intelligence continued to survive in popular idioms, such as "learning something by heart".<ref>[[#refHendrickson|Encylopedia of Word and Phrase Origins]]</ref>
Galen did a masterful job of tracing out the anatomical relationships between brain, nerves, and muscles, demonstrating that all muscles in the body are connected to the brain via a branching network of nerves. He postulated that nerves activate muscles mechanically, by carrying a mysterious substance he called ''pneumata psychikon'', usually translated as "animal spirits". His ideas were widely known during the Middle Ages, but not much further progress came until the Renaissance, when detailed anatomical study resumed, combined with the theoretical speculations of Descartes and his followers. Descartes, like Galen, thought of the nervous system in hydraulic terms. He believed that the highest cognitive functions—language in particular—are carried out by a non-physical ''res cogitans'', but that the majority of behaviors of humans and animals could be explained mechanically. The first real progress toward a modern understanding of nervous function, though, came from the investigations of Luigi Galvani, who discovered that a shock of static electricity applied to an exposed nerve of a dead frog could cause its leg to contract.

== See also ==
*[[Traumatic brain injury]]
*[[Brain (as food)|Brain as food]]

==Notes==
{{reflist|colwidth=30em}}

==References==
{{refbegin|2}}

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{{refend}}

==Further reading==
{{portalpar|Neuroscience|Neuro logo.png}}
*{{cite book|author=Junqueira, L.C., and J. Carneiro|title=Basic Histology: Text and Atlas, Tenth Edition|publisher=Lange Medical Books McGraw-Hill|year=2003|isbn=0-07-121565-4}}
*{{cite book|author=Sala, Sergio Della, editor.|title=Mind myths: Exploring popular assumptions about the mind and brain|publisher=J. Wiley & Sons, New York|year=1999|isbn=0-471-98303-9}}
*{{cite book|author=Vander, A., J. Sherman, D. Luciano|title=Human Physiology: The Mechanisms of Body Function|publisher=McGraw Hill Higher Education|year=2001|isbn=0-07-118088-5}}
*{{cite book |author= [[Piero Scaruffi|Scaruffi, Piero]]|title=The Nature of Consciousness |publisher=Omniware |year= |isbn=0-9765531-1-2 |doi=}}


==External links==
==External links==
*[http://www.claphampark.org.uk Clapham Park Project]
{{commonscat|Brain}}
* [http://www.howstuffworks.com/Brain.htm How Your Brain Works] at [[HowStuffWorks]]
* [http://www.stanford.edu/group/hopes/basics/braintut/ab0.html The HOPES Brain Tutorial] at [http://hopes.stanford.edu/ hopes.stanford.edu]
* [http://brainmuseum.org/ Comparative Mammalian Brain Collection]
* [http://www.sciencedaily.com/news/mind_brain/ Brain Research News from ScienceDaily]
* [http://braininfo.rprc.washington.edu BrainInfo for Neuroanatomy]
* [http://faculty.washington.edu/chudler/neurok.html Neuroscience for kids]
* [http://www.newscientist.com/channel/being-human/brain Everything you wanted to know about the brain] – Provided by ''[[New Scientist]]''.
* [http://www.biaq.com.au/ Fact sheets on brain injury - causes, effects and coping strategies]
* [http://purl.net/net/neurowiki Neuroscience wiki].
* [http://www.brainmaps.org/ BrainMaps.org], interactive high-resolution digital brain atlas based on scanned images of serial sections of both primate and non-primate brains
* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=000AF67F-28CD-1F30-9AD380A84189F2D7&pageNumber=1&catID=2 Scientific American Magazine (September 2003 Issue) Ultimate Self-Improvement]
* [http://cerebralhealth.com/neuroscienceresearch.php Brain Research and Information Network B.R.A.I.N.]
* [http://thebrain.mcgill.ca The Brain from Top to Bottom]

{{nervous system}}
{{Telencephalon}}
{{Diencephalon}}
{{Mesencephalon}}
{{Rhombencephalon}}


{{coord missing|United Kingdom}}
[[Category:Brain| ]]
[[Category:Central nervous system]]
[[Category:Neuroanatomy]]
[[Category:Organs]]


[[Category:Buildings and structures in Lambeth]]
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[[bs:Mozak]]
[[bg:Главен мозък]]
[[ca:Cervell]]
[[cs:Mozek]]
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[[da:Hjerne]]
[[de:Gehirn]]
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[[ps:ماغزه]]
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[[ru:Мозг]]
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[[uk:Головний мозок]]
[[ur:دماغ]]
[[yi:מוח]]
[[zh:脑]]

Revision as of 18:32, 13 October 2008

Clapham Park is an area in the Borough of Lambeth in London, to the south of central Clapham and west of Brixton.

The original Clapham Park estate was a speculative development by Thomas Cubitt, who bought 229 acres (0.93 km2) of Bleak Hall Farm in 1825, and marked out plots for building around the new broad, tree-lined streets of Kings Avenue, Clarence Avenue, Poynders Road and Atkins Road. It was planned to consist of extremely large detached houses in Cubitt's characteristic Italianate villa style, set in extensive grounds.

However, the ambitions of the developer were never fulfilled, and some plots remained undeveloped at the outbreak of World War I. Cubitt's own residence, Lincoln House, with its vast grounds, was demolished in 1905.

Rodenhurst Road, a street of large double-fronted semi-detached Edwardian houses was laid out on the site of Lincoln House. British statesman Arthur Henderson once lived at number 13 and there is a Blue Plaque on the house indicating this. Because of its leafy layout, Rodenhurst Road is often erroneously assumed to have been an original part of Cubitt's layout. The undivided properties remain among the most expensive in Lambeth.

Severance of the estate

From the 1920s, some of the undeveloped plots on the southern part of the estate were developed with medium-density terraced and semi-detached houses for sale. With the adoption of Poynders Road as the arterial "South Circular" road, this area is now severed from the area further north by traffic, and not generally referred to as part of Clapham Park. The site of one Cubitt villa was donated to the then Metropolitan Borough of Wandsworth as a park, and is now known as Agnes Riley Gardens after its benefactor.

The Clapham Park Estate

The area immediately to the east of the estate had been developed by the London County Council (LCC) in the 1920s as council housing, mostly in characteristic blocks of neo-Georgian brick flats. Following World War II most of the Cubitt houses were demolished and the northern part of the original area was redeveloped by the LCC to a very different Modern Movement style. Most buildings are set on an arbitrary diagonal axis to the existing street line, and visitors to this part of the estate get easily lost. Following completion of the scheme by the Greater London Council, the Clapham Park Estate became the largest single council estate within the new London Borough of Lambeth.

Lambeth Council also constructed flats west of Clarence Avenue, including three tower blocks (Barnsbury, Belgravia and Bloomsbury houses) commemorating Cubitt's more successful developments.

The Clapham Park Estate has had a concentration of social problems, which were not recognised statistically while the estate was divided between three local government wards. The estate was served by very few community facilities, and this was exacerbated by Lambeth's closure of the branch library in 2000. The journalist and commentator Polly Toynbee lived in a "hard-to-let" flat on the estate while researching her 2003 book Hard Work: Life in Low-Pay Britain

Clapham Park was selected as a pilot site for New Deal for Communities, which has brought some new education, training, health and community safety projects to the estate. Better management of Lambeth's housing has also alleviated some of the worst elements of physical disrepair of the estate. In 2005, tenants of the estate voted for a "stock transfer" to a housing association, and ownership and management of their homes transferred from the London Borough of Lambeth to Clapham Park Homes, the new community led housing association, on 27 June 2006. The transfer is closely linked to ambitious and controversial plans for large scale redevelopment of the estate, which would increase the number of homes, substantially increase housing density and diversify tenure.

Abbeville Village

From the 1880s the area to the west of Cubitt's land holdings between Clapham Common Southside and the site of Lincoln House was developed to more conventional housing designs. This area borrowed the name of Clapham Park, presumably because of its original social cachet. These streets have predominantly remained in owner occupation. The grid of late Victorian era streets around Abbeville Road is frequently referred to (particularly by estate agents) as Abbeville Village, although many independent local shops that gave the area a distinct character until the 1990s have made way for restaurants, cafes and bars, as the street has become the centre of local night life for the professional middle classes and shop rentals have increased exponentially.

External links

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