As neuroscience (more rarely singular: Neuroscience ) are referred to the scientific research areas in which design and function of nervous systems are examined. Due to the wide variety of methods used, neuroscientific research is carried out by scientists from many different disciplines such as physiology , psychology , medicine , biology , computer science and mathematics . Often there are also collaborations with related scientific areas such as information technology, computer science or robotics .
History of brain research
Finds from early Egypt show that surgical interventions in the central nervous system were carried out 5000 years ago. About 70 percent of the skulls in which there is evidence of such interventions have changed biologically after the operation, which indicates that the patient survived the operation by months or years.
Around 500 BC Alkmaion of Croton is said to have been the first to discover the optic nerves and other sensory nerves. Alkmaion developed the idea that nerves are hollow and enclose a medium ( kenon ) that guides the sensory impression to the brain. Hippocrates of Kos recognized that the brain functions as the seat of sensation and intelligence. Around 129–216 AD the functions of individual nerve tracts were described by Galen .
In the Middle Ages, knowledge of Western European brain research fell behind the level of antiquity. Research in the European area was primarily concerned with the monastic herbal studies.
The first sections were carried out during the Renaissance . The Italian Giovanni Alfonso Borelli (1608–1679) questioned the existence of a gaseous spiritus animalis for the first time . Instead, he suspected the existence of a fluid, the succus nerveus , which was pressed into the extremities by the hollow nerves and thus should induce the actions according to pneumatic principles.
The fact that electrical impulses flow via nerves was first described in the 18th century. A second important finding of the 18th century was that the cerebral cortex is functionally structured. Research into brain anatomy also made rapid progress from the 19th century. In the still young 21st century, neuroscience is developing primarily methodologically.
The field of research in neuroscience is the role of nervous systems of all kinds in the overall execution of the life processes of biological organisms.
In particular, the neurosciences are about the analysis of the structure and functioning of the central units of all nervous systems, the neurons and other cell types such as glial cells in particular . The peculiarities and effects of the networking of these cells to form neural networks in complex nervous systems are examined. Examples are the diffuse nervous system of the coelenterates , the ventral nerve cord of arthropods and the central nervous system of vertebrates .
Research directions in neuroscience, which are mainly concerned with the study of the structure and performance of the brains of primates (i.e. humans and monkeys ), are often referred to colloquially as brain or brain research .
In addition to experimental basic research , research is also carried out from a medical point of view into the causes and healing options for nervous diseases such as Parkinson's , Alzheimer's or dementia . The neurosciences also investigate cognitive information processing (neural processes in perception , formerly traditionally referred to as “ mental ” phenomena) as well as the origin and course of emotional reactions or broad phenomena such as consciousness and memory .
In recent decades, therefore, numerous, partly institutionally anchored collaborations between neuroscientists and researchers from other disciplines have arisen, with the closest relationships being with representatives of cognitive science , psychology and the philosophy of mind .
The neurosciences evade the attempt to subdivide them sharply into sub-areas according to various criteria. It is true that the disciplines could initially be classified according to the microscopic and macroscopic hierarchy levels considered (molecules, cells, cell structure, network, behavior ), but neurosciences tend towards a more functional perspective. In other words, the functional role of a microscopic element for a (macroscopic) system is usually examined one or more levels above.
The following is a possible rough division of the neurosciences, according to the levels, into four different disciplines:
- Clinical-medical subjects
The Neurobiology mainly deals with the molecular and cell biological basis of neuroscience. Other disciplines that work at this level are the neuroscientific branches of biochemistry , molecular biology , genetics and epigenetics , but also cell biology , histology and anatomy and developmental biology . The - controversially discussed - plant neurobiology deals with the expansion of neuroscientific knowledge from zoology to include plants .
Neurophysiology is at the center of the neurosciences . Although physiology is normally a sub-discipline of biology, it has a special role in neuroscience in that neuronal activity, and thus the "language of nerves", falls within the field of neurophysiology. Neurophysiology can be subdivided into electrophysiology and sensory physiology , but is also closely related to neuropharmacology , neuroendocrinology and toxicology .
Cognitive neuroscience occupies a central place on a higher level. It deals with the neural mechanisms that underlie cognitive and psychological functions. So she is primarily interested in the higher performance of the brain as well as in its deficits.
In 2000, well-known neuroscientists gave an international collaboration with psychoanalysis a platform by founding a separate specialist society, which they called The Neuropsychoanalysis Association .
The clinical-medical subjects deal with the pathogenesis , diagnosis and therapy of diseases of the brain and include neurology , neuropathology , neuroradiology and neurosurgery as well as biological psychiatry and clinical neuropsychology .
The methods of neuroscience initially differ in their applicability to humans. For the study of the human nervous system, predominantly non-invasive methods are used, i.e. methods that do not damage the system. In exceptional cases and in animal experiments, invasive procedures are also used. Lesion studies, for example, represent an exceptional case, which provide information on the localization of functions through a systematic comparison of damaged brains. However, the damage is not carried out in a targeted manner; rather, patients with brain injuries or strokes form the basis for the study. The most important neuroscientific methods are listed below.
- The psychophysics is exclusively concerned with the measurement capabilities of the brain as one complex within the organism. It provides clues to the range of possibilities that a living being has. Psychophysics is often brought together with anatomy when conducting lesion studies. Patients with brain lesions e.g. B. after a stroke are compared with healthy people. The comparison of the (psychophysical) possibilities of two neuronal systems with an intact or damaged brain makes it possible to assess the role of the damaged brain area for the abilities and capabilities. However, the lesion studies have the disadvantage that the location of the damage could only be determined after the patient's death. They were therefore very tedious, but for a long time they formed the basis of all neuroscientific studies and limited the speed at which neuroscientific knowledge was gained. In her methodology, the activity of nerve cells does not play a direct role in that the focus of the study is not the nerve cell but the entire system of the living being.
- With the development of devices that can directly or indirectly draw conclusions about the activity of the brain, the nature of the studies also changed. The development of electroencephalography (EEG) makes it possible to indirectly watch the brain work. The activity of nerve cells creates an electric field that can be measured outside the skull. Since a magnetic field also propagates orthogonally to every electric field, this can also be measured; this method is known as magnetoencephalography (MEG). Both methods have in common that they make it possible to measure the activity of large cell clusters with high temporal resolution and thus to obtain information about the sequence of processing steps. The spatial resolution is moderate, yet it allows researchers to gain knowledge about the location and time of neuronal process steps in living people.
- By means of computer tomography (CT), it has become possible to determine location and extent of a lesion also in living patients. This made lesion studies faster and more accurate, since the brain can be scanned immediately after damage and the anatomy of the damage can already provide information on possible (cognitive) deficits, which can then be studied in a targeted manner. Another side effect is the fact that the brain deforms from damage to the death of the patient, which makes it difficult to determine the exact anatomy of the damage. This deformation does not play a role in CT insofar as the time between damage and tomography is usually short. This also applies to magnetic resonance imaging (MRT / MRI, also known as magnetic resonance imaging). Both methods have good to very good spatial resolution, but do not allow any conclusions to be drawn about the activity of nerve cells. They represent the continuation of the lesion studies.
- Functional studies, i.e. studies that investigate the function of certain brain areas, only became possible when imaging methods were developed whose measured signal strength changes depending on the activity of brain areas. These methods include positron emission tomography (PET), single photon emission computed tomography (SPECT) and functional magnetic resonance tomography (fMRI / fMRI). They all generate a signal of moderate to good spatial resolution, but have the disadvantage of being practically blind to the temporal sequence of neural processes (in the millisecond range). A relatively new method is non-invasive near-infrared spectroscopy , which has good temporal resolution, but can only image small areas of the brain. In contrast to other functional methods, however, it can be used like an EEG mobile and in natural surroundings.
- In animal model systems or in clinical studies, invasive methods are also used that specifically change the properties of the nervous system or cause damage or injuries through measurement. On a global level, pharmacological agents in particular change the properties of neurons or other mechanisms relevant to neuronal activity, plasticity or development. In pharmacological intervention , depending on the substance, a brain area can be influenced or completely destroyed, or only a very specific channel or receptor type of the neuronal cell membrane can be influenced in the entire brain. The pharmacological intervention is therefore both a global and a specific functional method. Psychophysics, electrophysiology or (post mortem) histology are usually used to measure the effects of the intervention .
- The transcranial magnetic stimulation (TMS) allows short off areas of the brain. Although it is invasive, it is also used in humans because it is not expected to cause permanent damage. By means of a strong magnetic field, electricity is painlessly induced in whole brain areas, the activity of which has nothing to do with the normal task of the areas. One therefore sometimes speaks of a temporary lesion . The duration of the lesion is usually in the millisecond range and therefore allows insight into the sequence of neuronal processes. With repetitive transcranial magnetic stimulation (rTMS), on the other hand, areas of the brain are switched off for minutes by repeated stimulation by making use of a protective mechanism of the brain. The repeated simultaneous stimulation of entire brain areas leads the brain to believe that an epileptic seizure is imminent. As a counter-reaction, the activity of the stimulated brain area is suppressed in order to prevent the excitation from spreading. The temporary lesion created in this way now persists for a few minutes. The spatial resolution is moderate, the temporal resolution very good for TMS and bad for rTMS.
- By means of electrical stimulation of cortical areas, as with TMS, the processing of nerve impulses in certain brain areas can be briefly influenced or completely switched off. In contrast to TMS, however, the skull is opened for this purpose (since significantly stronger, painful currents must be applied from outside the skull) and an electrode is implanted in a brain area of interest. This allows a much more precise spatial determination of the affected areas. Electrical stimulation is mainly used in neurosurgery to determine the language centers that must not be damaged during operations, but also in animal models in order to be able to influence neural activity in the short term.
- Electrophysiology works in the opposite direction , which, instead of inducing currents in the brain, measures electrical signals from individual cells or cell groups. A distinction is made here between in-vivo and in-vitro experiments. In in vivo experiments, electrodes are placed in the brain of a living animal, either by permanently implanting them (chronic implant) or only temporarily in areas of the brain of interest (acute experiment). Chronic implants make it possible to study brain activity in an animal that is behaving normally. In vitro experiments study the electrical activity of cells and are not carried out on living animals, but only on brain tissue. The activity of the tissue does not correspond to the normal behavior of the animal, but techniques such as the patch-clamp technique allow much more precise conclusions to be drawn about the properties of the neurons in a brain area, since these can be studied systematically.
- Microscopy has always been important for studying the morphological structure of brain tissue . Newer techniques, especially multiphoton microscopy and confocal microscopy, allow a previously unimagined spatial resolution. Individual neurons can be measured in 3D and morphological changes can be studied in detail. Functional studies can also be carried out when using ion-sensitive or voltage-sensitive dyes.
- Theoretical neuroscience tries to understand the principles and mechanisms that underlie the development, organization, information processing and mental abilities of the nervous system using mathematical models. With the theory of dynamic systems , approaches from physics and mathematics are used. Many problems cannot be solved analytically and must therefore be simulated numerically. The field of computational neuroscience can be understood as a branch of research within theoretical neuroscience in which computers are used to simulate models. Since this is mostly the case, the terms “theoretical neuroscience” and “computational neuroscience” are often used synonymously.
- The techniques of genetics offer further fields of neuroscience at the cellular level . With their help, very specific genes can be deleted (e.g. knockout mouse ), modified or implemented ( e.g. Gal4 / UAS system ) in experimental animals in order to observe their significance for the nervous system. Virtually all of the methods listed above can be used on such mutants or transformants. A specialty is optogenetics , in which genetically modified cells can be activated or inhibited by irradiation with light. In addition, it enables the activity of entire populations of certain cell types to be observed under the light microscope.
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