The field of cognitive neuroscience overlaps with cognitive science and cognitive psychology . In contrast to cognitive psychology, however, the cognitive neurosciences do not try to understand the (human) mind (e.g. the formation of memories, thoughts, etc.), but rather deal with the underlying neurobiological processes. So cognitive psychology and cognitive neuroscience study different aspects of the same thing (e.g. reaction time , functional imaging ). They influence each other, as a more detailed understanding of the mental processes is helpful for understanding the underlying brain structures and vice versa.
Cognitive neuroscience is a very young field of research, the establishment of which led to numerous new findings and thus to a great leap in the study of the human brain.
At present, researchers in cognitive neuroscience usually come from an experimental , cognitive, bio- psychological , neurobiological, neurological, physical, or mathematical background. The methods used are therefore diverse and include psychophysical experiments and functional imaging, but also methods of neurophysiology and also neuroinformatics and computational neuroscience . The cognitive neuroscience as understood today has a long history, which was shaped by various philosophical and scientific approaches.
Studies on the functions of the brain can also be found in antiquity, for example in Galen (approx. 199–129 BC), who examined brain injuries in gladiators. Many of the ancient ideas remained unchallenged for a long time. The first approaches, which correspond to today's view of a functional structure of the human brain, only developed in the early 19th century with the emergence of phrenology according to Gall and Spurzheim . Many other assumptions in phrenology have meanwhile been refuted, but the approaches to functional specialization in the brain remain to this day.
In the years that followed, brain studies became an essential part of neuroscientific research, for example by researchers such as Broca and Wernicke . This led to the discovery of the functions of different brain areas. A special focus was placed on the investigation of patients with brain damage (brain lesions), as theories about the normal functioning of the brain could be derived from this. The study of brain lesions is known as cognitive neuropsychology and is still an important part of cognitive neuroscience today.
Experiments by Wilder Penfield and colleagues also provided far-reaching new insights into cognitive neuroscience. In the early 20th century, the research team performed numerous operations on human brains while the patients were conscious. In these interventions, which are painless for the patient, it was found that electrical stimulation of specific brain regions e.g. B. led to visual or acoustic phenomena or motor phenomena. From these experiments it could be concluded that certain brain regions are central to certain functions in the perception or behavior of humans, which for the first time provided an experimental confirmation of the assumptions about functional specialization in the brain. However, recent research suggests that different regions of the brain are only partially specialized in different functions.
Another important step on the way to today's understanding of cognitive neuroscience was the development of the assumption that the functioning of the brain is similar to that of a computer (computational approach). An early theory is the information processing paradigm , which gained popularity from the 1950s. According to this step-by-step paradigm, information must first be perceived in order to be fully processed, then attention must be given and stored in short-term memory. A more explicit computational model that developed from the 1980s onwards was that of neural networks . This assumes that the information processing takes place via the interaction of interconnected neural nodes .
The development of new imaging technologies from the 1970s onwards also made a significant contribution to modern cognitive neuroscience. The invention of fMRI (functional magnetic resonance tomography) deserves special mention . The fMRI provided the opportunity to observe the parts of the brain relevant to cognitive neuroscience without damaging the brain. Ultimately, then, this combination of imaging technologies and theories of cognitive psychology led to our understanding of cognitive neuroscience today.
Today, the discipline of cognitive neuroscience can be seen as the amalgamation of experimental psychology and neuroscience . George A. Miller and Michael Gazzaniga can be seen as the founders of this combined discipline . Alexander Romanowitsch Lurija is also to be regarded as a pioneer , who anticipated the merging of the aforementioned fields much earlier and linked neuroscience with psychology.
The starting point of cognitive neuroscience can be found in the originally philosophical discussion about the mind-body problem , i.e. the question of how physical mass (the brain) can generate psychological experiences (e.g. sensory perceptions). Three approaches to solving this problem have developed: dualism , dual aspect theory and reductionism .
The development of cognitive neuroscience and the use of neuroscientific methods within psychology has contributed greatly to the further development and research of many stalled psychological issues. Great progress has been made in the past to identify neurobiological correlates of behavior and processes and to understand the effects of damage in the brain on these processes. However, there are also risks associated with the growing importance of the neurosciences in psychology.
Current Risks in the Context of Cognitive Neuroscience
A reductionist perspective on cognitive neuroscience (also known as neuroessentialism) harbors risks for the entire discipline of psychology. It would mean that all human experience and behavior could only be explained with the help of brain processes. Traditional psychological disciplines, which tend to be more socially oriented, such as personality psychology and social psychology , would then be displaced by cognitive neuroscience. Experts argue, however, that a comprehensive understanding of psychological processes on the basis of the brain alone is not possible, but that multiple aspects and their interactions on different levels must be taken into account, for example cognitive and emotional factors, as well as contextual influences (see model of the levels of analysis in psychology , emergence ). Some of the risks associated with the growing role of CN in psychology will therefore be addressed below by way of example. Another problem of neuroscientific research in psychology are incorrect logical conclusions, i.e. those that go beyond the interpretations permitted on the basis of the current data situation and the methods used. In addition to the neuroessentialism already mentioned, this includes e.g. & B. the following aspects:
- Deriving causality from correlations : Correlative data only show that there is a connection between two variables. It cannot be concluded which of the two variables is the cause or effect.
- Neurorealism: Neurorealism is based on the assumption that neuroimaging data is reliable and objective, without questioning the complexity of the data collection and analysis. In this way, neuroscientific data is sometimes used uncritically by the general public as a validation or falsification of any phenomenon.
- Neuroredundancy: Neuroredundancy describes the fact that neuroimaging data is in some cases not able to generate additional information compared to simple and less complex survey methods (e.g. & B. Self-report questionnaires).
- Reverse Inference Problem: The reverse inference problem in cognitive neuroscience involves the incorrect conclusion that brain activation in imaging must necessarily reflect an underlying psychological state or cognitive process .
These flawed logical conclusions can lead to neuroscientific data not being adequately questioned and overrated. This can have an effect called " neuroseduction ". This refers to the phenomenon that people are more likely to be convinced of questionable conclusions from study data when neuroscientific data and explanations are included.
Research Development Risks
The reproducibility of studies is discussed in all areas of psychology. However, it is particularly relevant for the cognitive neurosciences, as several studies and analyzes show that neuroimaging studies in particular have some methodological weaknesses. Some weaknesses are listed here:
- Many studies in cognitive neuroscience are very complex and expensive, which is why they often only have a small number of test subjects. According to one estimate, the statistical power of neuroimaging studies is consequently only 8% on average and is thus significantly lower than the 80% aimed at by Cohen , which means that these neuroimaging studies are less likely to discover real effects.
- The Winner's Curse : In studies with insufficient statistical power, positive results are more likely to be random than in studies with adequate statistical power.
- The frequent multitude of analyzes per study of an inflation of errors of Art 1 .
- It has been shown that the reliability of fMRI studies, for example, is often far below the demands of other psychological measures such as questionnaires or interviews.
It is suggested to encourage collaboration between neuroimaging laboratories using the same methodological protocols. This increases the statistical power, avoids the winner's curse and minimizes the risk of false positive results.
In terms of research economics, there are still risks that can arise from the gain in the importance of neuroscience within psychology. On the one hand, the preferred funding for research projects with neuroscientific issues should be mentioned here. The priorities of government funding agencies, such as B. the National Institute of Mental Health (NIMH), seem to shift more in the direction of projects with a neuroscientific focus. The formulation of the strategic goals of the NIMH has z. B. increasingly oriented towards biological and imaging issues. This could put psychologists under pressure in their research to explicitly investigate neuroscientific questions or to use neuroscientific measures, even if these should be uneconomical. On the other hand, the effects on the personnel policy of universities are also discussed. So z. For example, on the APA website, the proportion of job advertisements in neurosciences, as a field of psychology, rose from around 40% (2011) to 33% (2012) to 50% (2013) within three years.
Risks in connection with the clinical-psychological application
Due to neuroscientific findings and the associated conclusions, mental disorders are conceptually currently increasingly understood as diseases of the brain. On the one hand, the approach of constitutive reductionism allows mental disorders to be viewed as brain diseases at the lowest level of analysis , since all psychological phenomena are mediated by neuronal factors . However, mental illnesses are associated with dysfunctions at higher levels of analysis and are also defined by them. For example, the ICD-10 diagnostic criteria for F diagnoses have so far been purely “psychological” and do not contain any neuronal, biological or chemical aspects.
The fact that mental disorders are also associated with changes in brain function does not mean that these changes are causal for the development of a mental disorder. The use of the term "brain disease" therefore harbors the risk of assuming a purely biological etiology for mental disorders . In clinical-psychological and psychiatric research, however, it is assumed that all disorders are the result of a multifactorial etiopathogenesis, consisting of a triad of genetic, biological and psychosocial factors.
Following the changed understanding of mental disorders, the treatment of these has also undergone a change. In psychotherapy , so-called “ brain-based ” (translated: brain-based ) psychotherapies have been developed, which are based on the findings of cognitive neuroscience. Proponents of these forms of therapy argue that neuroscientific findings contribute significantly to the design of effective psychotherapeutic interventions. However, it is questionable whether these findings actually generate an information base that goes beyond the information from visible behavior , affect and cognition . This is a practical example of neuroredundancy. In addition, the empirical examination of the benefits of “ brain-based ” psychotherapies poses a difficulty that arises from the lack of knowledge about the link between the brain and behavior ( explanation gap ;).
Physiological processes of the central and peripheral nervous system as well as their communication processes with the body are central to cognitive neuroscience.
Processes on the neural level as well as with regard to the interaction of brain areas up to cognitive phenomena such as experience and behavior are examined within the scope of various analysis levels. In this way, essential knowledge about the neuronal and brain physiology could be gained.
Billions of neurons make up the complex nervous system. Signals are transmitted from neuron to neuron via electrochemical processes. If an action potential is triggered on the axon hill, which lies between the cell body and the axon of a neuron, the voltage differences on the axon shift, which means that the signal can be carried on. At the end of the neuron there is the synapse , which either chemically, via the release of different neurotransmitters, or directly (electrical) transfers the electrical potential (the information) to the following neuron or a muscle. The information is encoded using the frequency of the rate of fire. Neurons specialize in specific frequencies and those with a similar functional specialization are grouped together. For this reason, certain brain regions are also specialized for certain information. Neurons form gray or white matter in the brain , where gray matter is made up of neuronal cell bodies and white matter is made up of axons and glial cells. The cerebral cortex and subcortex consist of structures of gray matter with a mass of white matter in between. Nerve fiber pathways connect different brain regions, both within the hemispheres (association pathways) and between the hemispheres (commissures with the corpus callosum as the central system) or between cortical and subcortical structures.
The basal ganglia are laid out bilaterally in the depth of the cortex . They are functionally relevant for the regulation of movements and the intensity of motor behavior. The reward learning and the formation of habits are also to be located in the basal ganglia. Lesions in this area lead to hypokinetics or hyperkinetics . Known diseases associated with the basal ganglia are e.g. B. Huntington 's disease or Parkinson's disease .
The limbic system relates the organism to the environment on the basis of current needs, the current situation and previous experiences. Different structures do this in different ways. The amygdala is considered to be central to the detection of fear and thus also to fear conditioning. The cingulate gyrus is associated with the development and processing of emotional and cognitive conflicts. The hippocampus is seen to be of great importance for learning and memory consolidation , as is the mammalian body . In the olfactory bulb , olfactory stimuli are detected. These stimuli can affect a person's mood and memory. Lesions in the limbic system manifest themselves in a variety of ways, depending on the affected region.
The diencephalon (diencephalon) can be roughly divided into the structures of the thalamus and hypothalamus divided. The thalamus interconnects all sensory impressions (except olfactory stimuli) and projects them into almost all regions of the cortex. The hypothalamus plays a central role in regulating vital functions such as body temperature, hunger, thirst, sexual activity and endocrine functions, e.g. B. Growth.
The midbrain is associated with orientation, auditory processing and motor behavior. The roof of the midbrain (tectum) contains two particularly important structures for cognitive neuroscience: The superior colliculi seem to integrate sensory information and thus enable the organism to quickly orientate itself towards conspicuous stimuli. The inferior colliculi, on the other hand, are considered central to auditory processing. The substantia nigra is closely related to the basal ganglia and is consequently understood as a crucial structure for movement patterns.
The hind brain (metencephalon) consists of the cerebellum (cerebellum) and the bridge (pons). The cerebellum is considered to be central to the integration of motor commands and sensory feedback. The bridge receives visual information to move the eyes and body. The Mark brain (medulla oblongata) controls vital functions such as breathing or sleep cycle.
Core methods of cognitive neuroscience
In the context of cognitive neuroscience, electrophysiological methods are often used, in which the biochemical and biophysical processes of the organism are examined with the help of the measurement of electrical potentials . In the context of cognitive neuroscience, these methods offer the possibility of measuring neural activity in a direct way. The procedures include single cell recording and electroencephalography (EEG).
Electrophysiological methods in cognitive neuroscience
Single cell leads
→ Main article: Single cell lead
In the case of single cell leads , an electrode is either inserted directly into a cell (intracellular measurement) or placed outside the cell membrane (extracellular measurement). In this way it can be measured how many action potentials a neuron triggers in response to a certain stimulus . When the activity of several neurons lying close together is recorded by an electrode, one speaks of multicellular leads . Special algorithms that break down the combined signal allow conclusions to be drawn about the contributions of individual neurons. The method is highly invasive and is therefore used almost exclusively on laboratory animals.
When it comes to the question of how many neurons are responsible for the representation of a single piece of information in the brain , the “sparse distributed representation” approach is currently assumed to be the most likely in cognitive neuroscience . On the one hand, this approach means that the information about a stimulus is distributed over several neurons instead of being coded by a single neuron ( grandmother neuron ). On the other hand, it is assumed that only some of the neurons in a neuron group carry information about a stimulus in order to save energy.
→ Main article: Electroencephalography
In electroencephalography , the electrical signals from the brain are measured non-invasively using several electrodes that are attached to the surface of the skull.
While a reference electrode (e.g. on the nose or the temporal bone) is needed, the skull electrodes themselves can be attached to many different locations. The 10-20 system of Jasper (1958) is often used to describe their position .
It is important to note that an EEG is hardly suitable for spatial location of an electrical signal, as the origin of the signal does not necessarily have to be in the immediate vicinity of the electrode. An EEG, on the other hand, has a very good temporal resolution and is therefore very well suited to measuring the temporal relationships between cognitive events and neural activity.
As EEG oscillations called one wavy oscillations in the EEG signal. Different vibration patterns are considered to be characteristic of the different sleeping and waking phases . They are also associated with various cognitive processes in the waking state, e.g. For example, alpha waves seem to be associated with increased alertness. The most common use of EEG is the method of event-related potentials (EKP, English event-related potentials (ERP)). The EEG waveform reflects neural activity from all areas of the brain. Some of them are specific to the current task (reading, arithmetic ...), but most of them arise from spontaneous activation or other neurons that are not directly related to the task. The actual signal, on the other hand, is very weak, so that it is difficult to draw conclusions from it. However, it is possible to increase the recognition of signals by averaging over several passes.
The graph is typically shown in a line diagram , with “time” on the x-axis and “electrode potential” on the y-axis. It consists of a series of positive and negative peaks ("deflections" = extreme values), which are named after their valence followed by the approximate time of the peak in milliseconds (e.g. P300, N400).
Examples of questions in the context of electrophysiological methods
→ Main article: Mental chronometry
Mental chronometry is the investigation of the temporal course of information processing in the human nervous system . As a basic idea, changes in the type or efficiency of information processing should become noticeable in the time it takes to complete a task. For example, a math problem typically involves a series of steps including visually recognizing the digits, performing calculations, and generating an answer. These can be viewed in the signal shown.
One ERP component that is relatively selective for processing any face is N170 . N250, on the other hand, is more powerful for famous or familiar faces and reacts to presentations of different images of the same person. It thus codes the peculiarities of the specific face.
Endogenous and exogenous ERP components
ERP components are classically referred to as exogenous or endogenous. Exogenous components depend on the physical properties of a stimulus (size, intensity , ...) and are evoked potentials. Endogenous components, on the other hand, depend on the properties of the task. Exogenous components are usually earlier than endogenous components.
Further development: magnetic encephalography (MEG)
→ Main article: Magnetic encephalography
The ability to pick up magnetic instead of electrical signals is the core property of the MEG. The device used requires extreme cooling (through liquid helium ) and isolation of the system in a magnetically shielded room. Accordingly, the costs for MEG are much higher than those for EEG. The much better spatial resolution, on the other hand, is a great advantage of the MEG.
When it comes to imaging (including imaging procedures or diagnostic imaging), a distinction is made in the cognitive neurosciences between structural and functional methods.
Types of Imaging
Structural imaging is fundamentally based on the knowledge that different tissues have different physical properties that can be used for a static mapping of the tissue structures. The most common structural methods are computed tomography (CT) and magnetic resonance imaging (MRI).
In contrast, functional imaging is the measurement of temporary changes in the brain that are associated with cognitive processes. The most common functional methods are positron emission tomography (PET) and functional magnetic resonance imaging (fMRI).
Experimental designs of imaging studies
Different methods are suitable for comparing brain activities under different conditions of an experiment, for example to identify certain functional specializations of individual areas, depending on the data available.
One of these methods is “cognitive subtraction”. Here, the brain activity in a task that requires the cognitive component to be examined is compared with the brain activity of a control condition that does not contain this cognitive component. The problem here is the assumption of “pure insertion”, ie the assumption that adding a component does not affect the other components included in the task. However, research has shown that the resulting interactions change the task and the imaging data become ambiguous. In order to reduce the problem of interactions, instead of “cognitive subtraction” using “cognitive conjunction”, more than two conditions that have a cognitive component in common can be compared with one another.
“Functional integration” can be used to find out how different brain regions communicate with one another. It is examined to what extent the activity in different brain regions is dependent on one another and the correlation between these activities is examined.
With regard to the grouping of the stimuli, a distinction is still made between block design and event-related design. In the block design, the stimuli that belong to the same experimental condition are grouped. In some experiments, however, it is not yet possible to group the stimuli before they are carried out because they differ subjectively for each test person and are classified individually. So also with the investigation of the tongue tip phenomenon . In such cases, an event-related design is recommended.
Analysis of imaging data
Due to potential individual differences and recording deficiencies (e.g. exposure, technical difficulties), error-free statistical analysis and interpretation of functional imaging data is more of a challenge. A multi-level processing of the data obtained is necessary in order to be able to average the personal data and carry out a statistical analysis .
This can include the following steps:
- the correction for head movements during the measurement
- the co-registration
- the stereotactic normalization
The co-registration includes the comparison of functional images with higher-resolution structural images. In stereotactic (spatial) normalization, the brain is divided into voxels (data points in a three-dimensional grid). The XYZ coordinates determined are assigned to the corresponding voxel coordinates of a standard reference brain, the so-called Talairach coordinates, in order to enable the standardized comparison of the activation patterns of several people within a uniform three-dimensional reference space. During the subsequent smoothing, part of the original activation level of a certain voxel is distributed to neighboring voxels in order to improve the signal-to-noise ratio . In the last step, the statistical data analysis is carried out separately for each voxel and the associated significance correction for multiple comparisons (see also alpha error accumulation and false detection rate).
Interpretation of imaging data
In functional imaging, an area is interpreted as activated if it differs statistically significantly from the control condition. If an area is active during a certain task, the causal inference cannot be drawn about the cognitive necessity of this area for this task (reverse inference problem). Alternative explanations are, for example, inter-individual cognitive strategies, a more general, superordinate role of the area (e.g. attention), inhibitory neuronal activity or chance. Accordingly, imaging studies cannot completely replace lesion studies . It is so far unclear whether imaging can be used to differentiate between excitatory and inhibitory processes. The possibility of being able to “read minds” using imaging is still a long way off.
Another core method of cognitive neuroscience is looking at patients with brain lesions (e.g. as a result of neurosurgical interventions, strokes, trauma, tumors, viral infections or neurodegenerative diseases). It observes which functions are retained in the brain and which fail or are restricted if a certain area fails. Subsequently, conclusions can be drawn about the function of the area. Investigations of this kind belong to the field of neuropsychology , which also includes clinical sub-areas.
This has developed in two different directions:
The classical neuropsychology tried the function of a brain region of patients with a lesion in this region derive. To do this, the pattern of restricted and functional skills is examined. The determined ability pattern is associated with specific brain regions. Group studies are the preferred method.
In contrast, cognitive neuropsychology tries to derive “building blocks of cognition” from the pattern of restricted and functional abilities that can be viewed independently of certain brain regions. The preferred method is individual case studies.
Examination of naturally occurring lesions
From the observation that patients with a lesion in area X can solve task A but not task B and patients with a lesion in area Y can solve task B but not task A, one can deduce that these two brain areas ( X and Y) differ in their functionality. This idea of “double dissociation” is used in lesion studies in order to be able to delimit the functionality of different brain areas.
Individual case studies enable the specific examination of brain-damaged patients. They play an important role in determining components of cognitive systems. Case studies are recognized as a valid research method and provide data with which theories can be tested, modified and further developed. However, new theories cannot be derived on the basis of observations of an individual case, since generalizations are only possible to a limited extent. It is therefore important to estimate the extent to which results can be generalized.
Group studies can address different types of questions that differ from the case-by-case approach. For this purpose, mean values are mainly calculated in order to allow generalizations to general cognitive mechanisms. Since lesions are usually large and rarely confined to the region of interest, examining multiple patients offers the advantage of being able to localize which region is essential for a particular task.
Investigation of artificially created lesions
Experimental lesions in animals
The examination of animals with experimental lesions covered by the concept of behavioral neuroscience ( behavioral neuroscience ). By surgically creating artificial lesions, it is possible to compare the condition before and after the operative lesion.
Methods used to cause lesions are:
- Aspiration, the "suction" of a certain region
- Transection, the severing of bundles of white matter
- Neurochemical lesion based on toxins
- Reversible, temporary lesions, e.g. B. by pharmacological manipulation or cooling
It should be noted that some difficulties arise when examining animal models, e.g. B. animal welfare. For ethical reasons, experimental lesion studies are not allowed on humans. Instead, magnetic or electrical methods are used, which only affect brain functions for a short time.
Magnetic Methods (TMS)
Transcranial Magnetic Stimulation (TMS) is another lesion method in cognitive neuroscience. The brain is stimulated with the help of a magnetic coil, which can temporarily interrupt cognitive functions. This disruption is called a reversible or “virtual” lesion.
The right time and place for the TMS impulses must be found for every question. The point in time can be derived from theoretical considerations or varied experimentally. Alternatively, a whole series of pulses can be used, which is called repetitive or rTMS. Studies on perception, for example, tend to use individual impulses, studies on higher cognitive functions (such as memory and language) tend to use rTMS.
Orientation points on the skull (e.g. on the inion, an elevation on the back of the head) are used to identify critical regions. It can be a precise point or a grid of e.g. B. 6 points can be checked in a 2 x 3 cm area. Correspondingly, the adjacent brain regions are used as control regions in order to check the effect of the stimulation. If there is reason to suspect that the cognitive function is lateralized, the same point in the other hemisphere can also be stimulated as a control value.
It makes sense to use non-critical regions or time windows as control conditions, as peripheral effects also occur with TMS (e.g. loud pulse noise, twitching of facial nerves and muscles) and, without suitable control, can distort the measurement results.
Electrical methods (tDCS)
There are several methods in the methods of stimulating the brain with electric current, some of which are more invasive than others. Transcranial direct current stimulation (tDCS) only uses a very weak current pulse compared to electroconvulsive therapy (ECT), for example . In tDCS, a stimulating pad is placed over the region of interest and a control pad is placed over the corresponding region of no interest. After 10 minutes of stimulation, the person to be examined performs a cognitive task. The results are then compared with those of a sham stimulation.
While in the ECT the electrical impulse is conducted from the anode (positively charged) to the cathode (negatively charged), i.e. cathodically, the stimulation in the tDCS takes place either anodically or cathodically. Cathodic tDCS interrupts and tends to worsen performance. The cognitive excitability is reduced, that is, the spontaneous rate of fire of the neurons is reduced. This affects the excitatory glutamate system. The anodic tDCS, on the other hand, tends to improve cognitive excitability, as the inhibitory GABA system is influenced, so that performance is increased and the spontaneous rate of fire of the neurons increases.
Central areas of investigation in cognitive neuroscience
In the following some central research areas in cognitive neuroscience are presented.
The cognitive neurosciences deal centrally with the processes of brain development, in which a distinction is made between structural and functional brain development.
Structural brain development
Structural brain development is the formation and maturation of the brain. The nature-nurture debate is a fundamental debate in the cognitive neurosciences. It deals with the question of the extent to which cognition and behavior are determined by genetic or environmental influences.
The probabilistic approach (Gottlieb, 1992) is considered to be predominant here. In addition to genetic influences, he assumes that the environment has a strong influence on the brain structure. Accordingly, different environmental influences change the gene expression and vice versa. Over the entire lifespan, all everyday experiences have an impact on brain development. This changeability of the brain is called neural plasticity . A distinction is made between prenatal and postnatal phases of brain development.
Prenatal brain development
Prenatal brain development refers to brain development in the womb. The nervous system develops from the neural tube , which emerges from the neural plate and is organized in bulges and convolutions. Different parts of the brain arise from these. At the trough of the neural tube there are tissue areas with increased cell proliferation , so-called proliferation zones. There, neurons and glial cells are formed through rapid cell division of the precursor cells. These move through migration to the places where they are needed on the mature brain. Radial glial cells serve as a scaffold along which neurons can migrate. In addition, older cells are passively displaced by the newer cells and pressed against the surface of the brain.
Postnatal brain development
Most neurons are formed before birth. After birth, brain growth takes place through the formation of synapses ( synaptogenesis ), dendrites and axon bundles, and myelination . Fine-tuning and networking of existing structures leads to more efficient functionality. Superfluous synapses are eliminated.
Protomap and protocortex theories of brain development
There are two central theories that investigate the question of how and when the regional organization of the brain structures occurs.
The Protomap theory (Rakic, 1988) relates to prenatal brain development . It says that genetic instructions (transcription factors) and their dosage determine which characteristics neurons have and which function they will assume in the future. In simplified terms, a signal above a certain threshold leads to different characteristics than below this threshold.
In contrast, there is the protocortex theory (O'Leary, 1989), which relates to postnatal brain development . Different regions of the cortex are considered to be initially equivalent and are only specialized through projections from the thalamus . These projections, in turn, are influenced by postnatal sensory experiences. This leads to the assumption that structural regions of the cortex can be exchanged at the beginning of brain development and receive their function from the thalamus in their new position. Accordingly, there seem to be both genetic and environmental influences on the structural organization of the brain. The protomap and protocortex theory are not mutually exclusive.
Functional brain development
Based on Konrad Lorenz's concept of childlike imprinting , it was initially assumed in cognitive neuroscience that human development takes place in so-called critical phases. These describe narrowly defined time windows in which the individual must be exposed to relevant environmental stimuli in order to have certain learning experiences and consequently to develop further. If this time window is exceeded without the confrontation with these impulses and the impulses from the environment were not given, the learning experience can no longer be made. Alternatively, however, the concept of the “ sensitive phase ” is preferred in science . A sensitive phase is used when impulses from the environment are not deterministically an ongoing learning process at a certain point in time. Cognitive neuroscience also investigates the extent to which human development is shaped by innate knowledge and behavioral structures. The fact that certain structures are innate is shown, for example, by the fact that certain perceptual preferences and abilities have been present since birth and are expressed in behavior without the corresponding learning experiences having already been made (e.g. preference for sweet food in newborns and children) . It is assumed that willingness to learn with regard to certain aspects, but also neural systems, are innate. However, these neural systems can be broken down by a lack of experience and impulses from the environment. The environment and experiences of an individual play a central role in their development. The reason for this is that most genes are not solely responsible for a certain function, but interact with the environment. These system-environment interactions are primarily researched in behavioral genetics , for example using twin research and adoption studies .
In addition, cognitive neuroscience also deals with processes of action planning and execution. In a hierarchical system of action and movement, different levels of perception , cognition and motor skills interact with one another. An action is planned based on goals and intentions. In addition, there is a need for perceptual, proprioceptive and motor systems through which humans can perceive the environment and interact with it. The brain does not recalculate action sequences from scratch every time. Generalized motor programs encode general aspects of movement to allow for faster response. The process of combining all action-relevant information is called sensorimotor integration . The result of the interaction of all the processes mentioned manifests itself in an action carried out.
Neuroanatomical basics of action control
Due to the complex networking of perception, cognition and motor skills for action control, a large number of brain areas are considered to be involved. The frontal lobes are considered to be central to action control . From the posterior parts to the anterior areas, their functions become more and more unspecific. Anterior parts are more likely to be involved in controlling behavior without necessarily leading to visible actions.
As the posterior part of the frontal lobe, the primary motor cortex (M1) controls the execution of movements. It is organized somatotopically, with the right half of the body being controlled by the left part of the motor cortex and vice versa. In contrast to the movements of the limbs, eye movements are not controlled by the M1, but by the frontal eye fields (FEF).
The premotor cortex is anterior to the M1. The lateral premotor cortex is primarily associated with movements that are related to objects in the environment (e.g. reaching for the remote control). It receives information from the parietal cortex via the dorsal path of vision. The medial premotor cortex (or supplementary motor area; SMA) is associated with spontaneous, well-learned actions - especially with actions that are relatively independent of the perception of the environment (e.g. playing a familiar melody on the piano). Less information about the position of objects (dorsal path) is required for this, instead the SMA mainly receives signals about the position of the limbs.
The prefrontal cortex is involved in planning and in higher cognitive aspects of action control. It serves to select the premotor area (SMA or lateral premotor cortex) and maintains the goals of the action. The activation of the prefrontal cortex occurs independently of the movement itself, so it is only active during planning and decision-making.
Neural mechanisms of sensorimotor integration
The intraparietal area and frontal brain regions
Visual, cognitive and motor information is brought together in a network of parietal and frontal regions. It can be assumed that the anterior intraparietal area and the frontal areas connected to it primarily encode abstract properties of an action and are probably responsible for the transfer of skills from the body to a tool.
Deficits with regard to the sensorimotor integration processes can lead to various disturbances in the course of action. The most common form of damage that occurs is ideomotor apraxia .
When integrating sensory and motor information, different areas of the brain are active. The neurons involved each encode various pieces of information from the overall process.
- Neurons that code the special aspects of an action : Humans have a stored repertoire of different sequences of actions. These include a. grasping or holding an object. Fine finger movements are neural coded differently than a grip with the whole hand.
- The coding of sensory information across different sensory modalities : There are neurons that react both to the perceived position of a limb in space and to the visually perceived position. This means that our visual perception is always processed relative to the body position.
- Neurons that code properties of objects that are relevant to action : These neurons react v. a. on the shape of the objects, their size and their orientation in space. These neurons are located in the anterior intraparietal area, which reacts primarily to changeable shapes and 3D objects.
The role of subcortical structures
Subcortical structures are important for preparing and performing actions. Two main types of subcortical loops are believed to be involved in creating movement:
- The cerebellum loop leads through the cerebellum and is responsible for coordinating movements. It uses sensory and motor information to coordinate precise timing and accuracy of movements.
- The basal ganglia loop consists of five different loops that project to different structures in the basal ganglia and the cortex and regulate different aspects of behavior. They consist of excitatory (excitatory) and inhibitory (inhibitory) pathways. Basal ganglia do not generate signals for movement, but rather change the activity in frontal motor structures (e.g. SMA) and thus regulate the probability and type of movement (e.g. force). The most relevant loop, the motor circuit , runs through dorsal areas of the basal ganglia to premotor areas and the SMA. It is particularly important for initiating and executing internally generated movements, sequences of actions and for procedural learning .
Diseases of the basal ganglia
If there are malfunctions in the basal ganglia, diseases can occur which are divided into hypokinetic or hyperkinetic manifestations. Hypokinetic diseases are characterized by a reduced incidence of spontaneous movement. An example of this is Parkinson's disease . Hyperkinetic diseases are characterized by an increased incidence of spontaneous movement, for example Huntington's disease , Tourette's or obsessive-compulsive disorder (OCD) .
Research into action control in the context of cognitive neuroscience
The Supervisory Attentional System Model
As part of cognitive neuroscience, the Supervisory Attentional System Model (SAS model) was developed by Norman and Shallice to explain the planning of goal-directed actions. It describes two systems that work together:
The contention scheduling system selects one of many possible schemes for action. The selection of a scheme depends on the one hand on the environment (sensory input), which can activate automatic patterns of action.
On the other hand, the contention scheduling system is influenced by a second system, namely the so-called Supervisory Attentional System, which represents the current and future goals / needs of the person. This is particularly active when situations require the interruption of automatic courses of action and the execution of new, inexperienced action sequences.
The contention scheduling system calculates the information from the sensory input and the supervisory attentional system and selects the scheme with the highest activation for action. This should meet the current needs of the person and match the existing environmental conditions.
Damage to regions of the prefrontal cortex does not mean that movements and actions are necessarily impaired; they are just poorly organized and do not necessarily reflect the person's goals. Typical mistakes in PFC lesions can be explained with the help of the Supervisory Attentional System model: The lesion results in an imbalance in the information that reaches the contention scheduling system. Typical mistakes here are, for example, perseveration , utilization behavior or frontal apraxia .
Actions and free will
In the Libet experiment, it was shown that the motor center of the brain began preparing for a movement before a person was even aware that they had decided to perform it. A radical interpretation of these results would be that free will does not exist. Libet's experiments sparked controversial discussions about free will.
Understanding and imitation of action
According to cognitive neuroscience, there are two ways of reproducing the observed actions of others:
- Mimicry only takes place via sensorimotor integration. Goals and intentions of the observed acting person are not explored.
- Imitation is a more complex form of reproduction. The mirror neurons are considered to be central to this type of process . They describe a group of nerve cells that react both during the execution and the observation of targeted actions. Mirror neurons do not differentiate whether these are carried out by one's own self or by other people. They seem to respond preferentially to precisely targeted actions, so what matters is the expediency of the action. It is assumed that mirror neurons in humans are mainly located in Broca's area (especially Brodmann area 44), which extends into the premotor area.
Actions with objects
The interaction of different senses makes it possible to use objects in a targeted and functional way. The information about where an object is located in the room must be linked to motor information in order to adapt the action to the spatial conditions. In addition, there is an understanding of the functions with which the objects are associated.
Ungerleider and Mishkin (1982) first described that the visual processing of objects involves two paths: the ventral and the dorsal path . The ventral path or “what path” extends from the occipital to the temporal lobe and is responsible for the explicit perception of an object. Lesions here usually result in visual agnosia . The dorsal path, on the other hand, is referred to as the “where path” or sometimes the “how path” and extends from the occipital to the parietal lobe. He is responsible for the perception of action-relevant properties such as the size or position of objects. Lesions here, for example, result in optical ataxia .
Dissociations between visual perception and the visual control of actions can also be observed in people without lesions. With visual illusions such as the Ebbinghaus illusion , objects of the same size are actually perceived as different in size. The illusion thus influences the visual perception, but not the action on the object.
Tool in the cognitive-neuroscientific sense
Tools in the cognitive-neuroscientific sense differ from other objects in that they are associated with certain sequences of action and corresponding functions. Based on fMRI studies, it was found that the left parietal lobe (including the anterior intraparietal area) and Broca's area only reacted when looking at tools in the sense described above, but not to other object classes.
→ Main article: Executive functions
Another important research topic in cognitive neuroscience is human self-regulation and control, largely prescribed within the so-called executive functions .
Neuroanatomical basics of executive functions
Research in the context of cognitive neuroscience associated executive functions primarily with the prefrontal cortex of the frontal lobe, although other regions could also play a role. In general, the prefrontal cortex is considered to be important in controlling (especially non-automated) movements and cognitive processes with regard to mental simulation. In addition, control processes and storage components of working memory run via the prefrontal cortex.
The prefrontal cortex is anatomically divided into its lateral, medial, and orbital surface. The lateral prefrontal cortex is primarily associated with sensory inputs. It receives visual, somatosensory and auditory information as well as inputs from multimodal regions that are integrated across all senses. In contrast, the medial and orbital prefrontal cortex is considered to be more closely connected to medial temporal lobe structures, which are considered central to long-term memory and the processing of emotions .
In the course of numerous examinations, an activation of the dorsal part of the anterior cingulate cortex was observed when executing executive functions. It is discussed that it has a predominant role in the detection and monitoring of errors in the processing of tasks.
Research into executive functions
The research of executive functions in the context of cognitive neuroscience happens for example by means of tasks
- Task setting (solution generation with a given start and finish point, e.g. using the Tower of London task )
- Inhibition (overcoming habitual reactions, e.g. with the help of the Stroop effect )
- Task switching (switching between actions when the task requirements change, e.g. using the Wisconsin Card Sorting Test (Milner, 1963; Nelson, 1976))
- Multi-tasking (performing several tasks in parallel, e.g. using the Six Elements Test (Shallice & Burgess, 1991)).
Theories of Executive Functions in Cognitive Neuroscience
In the context of cognitive neuroscience, many approaches and models have emerged to explain the structure of executive functions. These differ in the extent to which the executive functions are subdivided into module-like processes or are designed as a uniform area.
"Hot" vs. "Cold" control processes
A hot control process is the control through affective, profit-related or reward-related stimuli (e.g. money for humans, feed for animals). These processes take place automatically and are mainly associated with the orbitofrontal cortex, but also with the ventromedial prefrontal cortex. Cold processes, on the other hand, which are predominantly associated with the lateral prefrontal cortex, refer exclusively to cognitive control processes. That is, they are responsible for planning, problem solving, or inhibition.
Damasio's “hypothesis of somatic markers” (1996) provides an explanation for patients who, due to a brain lesion of the prefrontal cortex, show difficulties in their behavioral regulation, although they have passed tests regarding their “cold” processes. According to this hypothesis, somatic markers link previous situations (which were stored in the cortex) with the associated feeling (stored in corresponding regions, e.g. the amygdala) and the physical condition (e.g. in the insula). The somatic markers are presumably stored in the ventromedial frontal cortex and play a central role in controlling current behavior.
The Multiple Demand Network
Another central question in cognitive neuroscience is whether the lateral prefrontal cortex can be divided into further functional subunits. Duncan provides a possible answer to this question with the theory of the Multiple Demand Network. According to the theory, the Multiple Demand Network includes regions of the lateral prefrontal cortex, the anterior cingulate cortex, and the parietal lobe (particularly those around the intraparietal sulcus). It is also closely associated with the concept of fluid intelligence , since associated tests (e.g. Raven's matrices) show a very similar neural activation pattern in fMRI (Duncan, 2010; Woolgar et al., 2010). According to the current state of research, all executive functions use the same network. Therefore, the Multiple Demand Network is characterized as an undifferentiated unit, the theory therefore denies further functional subunits in the lateral prefrontal cortex.
Organization: posterior to anterior?
Another research focus in this context is the hierarchical organization of the prefrontal cortex. Depending on the complexity of an executed task, different areas of the prefrontal cortex are activated. If you look at the anterior part of the prefrontal cortex, it is active during multitasking. If a person performs the same tasks one after the other, the anterior part of the prefrontal cortex remains inactive, while posterior areas of the prefrontal cortex are active.
Based on these findings, Koechlin and Summerfield (2007) set up the theory of the hierarchical organization (posterior to anterior) of executive functions.
According to the theory, predominantly posterior areas are active in the implementation of simple individual stimuli (“press the left button when green”). In the case of more complex stimuli (“when green press the left button, but only if a vowel is present”), predominantly anterior areas of the prefrontal cortex are activated.
Functional differences between the hemispheres are controversial in the context of cognitive neuroscience.
In a model by Stuss and colleagues based on lesion studies (1995), the left lateral prefrontal cortex is regarded as specialized for task setting, while the right lateral prefrontal cortex is specialized for task monitoring.
An alternative view of the function of the right (inferior) lateral prefrontal cortex is that it is functionally specialized in inhibition.
Social and emotional processing in the brain
Role of cognitive neuroscience in theories of emotion
Cognitive neuroscience was also able to make significant contributions with regard to the perception of emotions and social behavior. Research on the connection between physiological processes and the perception of emotions existed early on.
The James-Lange theory deserves special mention , it describes the origin of emotions . According to the theory, a stimulus is first followed by a physical reaction (e.g. muscle tension, changes in blood pressure ...) and then the emotional experience through perceiving this reaction. However, it was found that emotional experience is also possible without a physical reaction. The physician Walter Cannon also argued that the body reactions could not explain the differences in the spectrum of emotions. The Cannon-Bard theory emerged from these findings . According to this theory, the emotional experience in the brain takes place before the physical reaction. The neuronal emotion center should be the hypothalamus.
Paul Ekman categorized emotions into so-called basic emotions (joy, anger, disgust, fear, contempt, sadness and surprise), the origin of which he saw primarily in human genetics. Ekman also assumes that every basic emotion has a distinct neural correlate, but this has not been confirmed.
Neural correlates of emotion processing
The cognitive neurosciences consider the following brain regions to be particularly relevant for the neuronal processing of social and emotional processes: the amygdala , the insula , the orbitofrontal cortex, the anterior cingulum and the ventral striatum .
The amygdala is mainly discussed in the context of remembering emotional experiences. This influence is particularly evident in experiments on fear conditioning. It is believed that activation of the amygdala provides feedback on whether a stimulus or behavior is rewarded or punished. In the past, the amygdala was reputed to be the fear center of the brain. But now it is more believed that it is part of a larger network that encodes and decodes fear.
With regard to the insula, some findings show connections with aspects of pain and taste perception. It can happen that with some island lesions the emotion of disgust is less well recognized in other people's faces.
The orbitofrontal cortex is considered to be central to the evaluation of perceived stimuli in the context of the current situation. It plays a major role in unlearning conditioned stimuli (extinction).
The anterior cingulum is decisive for assessing which behavior leads to a reward and which leads to punishment.
The ventral striatum is part of the dopaminergic system and is associated with the encoding and anticipation of rewards. Any deviation from expectation is accompanied by a change in the activity of the striatum.
Faces convey important information about how someone feels and what someone is planning. In addition to this social information, the identity of the counterpart must of course also be determined. There are two models that both assume that there are two different mechanisms for doing this.
In “Single Route Detection” (Bruce and Young, 1986) the experts assume that there are fixed routes for each individual emotional facial expression. In the neuroanatomical model by Haxby (2000), a distinction is made between representations of faces that remain constant over time and representations of the face that can change over time. Representations that remain constant over time are important to recognize a person's identity. These are stored in the fusiform face area. Facial expressions that can be changed over time, on the other hand, are required for the recognition of facial expressions and are to be located in the superior temporal sulcus (STS).
There is also a superordinate system for recognizing emotions (Heberlein and Adolph's "simulation theory"). According to this theory, in order to understand an emotion of another, we activate the same affective path in order to reproduce the corresponding feeling in us.
In addition, the muscles that display the respective emotion as an expression on the face are also activated. Not only seeing, but also the activation of the muscles that are typical for the emotion leads to the recognition of the other's emotion.
The recognition of facial expressions is also used to adapt one's own behavior. In so-called “ social referencing ”, for example, an emotional reaction of another person (for example that of one's own mother) to a previously neutral sensory impression can lead to one approaching or turning away.
Empathy and the Theory of Mind (ToM)
There are also important findings of cognitive neuroscience with regard to empathy , the affective, as well as the theory of mind , the cognitive component of feeling the mental states of other people. Singer et al. (2004) were able to determine, for example, that the pain experienced by a loved one is divided in the sense that not only the brain regions of anticipated pain of others are active, but also one's own pain regions. So you feel the pain of others in the region for your own pain. Through fMRI experiments and lesion studies, three important brain regions in particular were identified that are related to thinking about mental states: the medial prefrontal cortex, the temporal pole and the transition area from the temporal lobe to the parietal lobe.
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