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Samenvatting cognitive neuroscience deeltentamen 1
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- Universiteit Utrecht (UU)
Dit is een uitgebreide samenvatting met ook afbeeldingen van de hoofdstuk 1-7 uit het boek principles of cognitive neuroscience.
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Voorbeeld van de inhoud
Cognitiveneuroscience
literatuur
Chapter 1
Cognition refers to a set of processes (cognitive functions) that allow humans and many other animals to
perceive external stimuli, to extract key information and hold it in memory, and ultimately to generate
thoughts and actions that help reach desired goals.
The mind consists of our subjective, conscious experiences. We, however, restrict the use of mind to the
subjective sense of self, and we use cognition or cognitive functions to describe specific sorts of
information processing studies by cognitive neuroscientists.
Behaviorism rejected subjective work on mental functions as being outside the domain of proper
scientific inquiry. Experiments carried out by behaviorists (John Watson, B.F. Skinner) examined how
changes in stimulus presentation could shape how individuals adapt their behavior to the demands of the
environment.
Behaviorists did noy deny the existence of mental states, but they dismissed those states as inappropriate
topics for scientific study.
George Miller: showed that people are able to represent only about 7 unique items at one time
(immediate memory). Memory, for Miller, was not a passive representation of sensory stimuli, but an
active recoding of the information the stimuli carried.
The field of artificial intelligence suggested that elementary computations could combine in unexpected
ways to support complex reasoning.
Chomsky argued that behaviorism could never explain the structural and generative properties of mental
phenomena such as human language. So, psychologists began to involve more human participants in their
research.
The term cognitive science unifies research on mental processes regardless of the specific topic,
experimental approach, method, or even discipline.
The elements of cognitive models are sometimes called psychological constructs, in recognition of the
face that they are created to help explain diverse phenomena without reference to their ultimate causes
in the brain.
The field of neuroscience is concerned with how the nervous systems of humans and other animals are
organized and function.
By the early nineteenth century , physicians had become interested in the functional properties of the
cerebral cortex. Frans Joseph Gall had long suspected that differences among individuals in their cognitive
,functions and personality traits were associated with different parts of the cerebral cortex, and he
hypothesized that the size of the cerebral cortex could be mapped by measuring bumps on the overlying
skull. This led to a new approach, called phrenology. This approach contributed to localization of
function: the idea that different parts of the brain contribute to different sorts of information processing.
Santiago identification of neurons. Signals are transmitted long distances along neuronal axons by
action potentials. Neurotransmitters are now known to be released by the terminals of neuronal axons at
specialized contacts called synapses, where the transmitter then bind to receptor molecules on target
neurons and other cells, thus altering the membrane potential of the cell contacted.
Charles Sherrington experimented on animals. Wilder Penfield translated this work to humans in a less
invasive manner. He exposed the cortex to weak electrical currents. Changing the location of stimulation
and monitoring the resulting sensations allowed Penfield to create a systematic map of the
somatosensory cortex.
Cognitive neuroscience is defined by work at the intersection of cognitive science and neuroscience.
The search for neural correlates of cognition: one common misconception that cognitive neuroscience
simply maps the brain regions that are activated during a psychological process.
The study of individual differences is a major area of research.
Using multiple methods provides two critical advantages:
Convergence describes the approach of combining results from multiple experimental paradigms
to illuminate a single theoretical concept.
Cognitive neuroscience also benefits from the complementarity of its research methods, each of
which provides a different sort of information about brain function.
Methods for combining information across multiple studies are called meta-analysis techniques.
Qualitative meta-analysis: a research team first identifies a comprehensive set of studies on the
same cognitive function and then looks for similarities among their results
Quantitative meta-analysis: combine results from multiple studies into a single statistical
framework
Semantic meta-analysis: combine studies according to similarity in their underlying concepts.
Chapter 2 The methods of cognitive
neuroscience
Neuroscience based approached can be divided into two broad categories: (1) studying changes in
cognitive behavior when the brain has been perturbed in some way, and (2) measuring brain activity while
cognitive tasks are being performed.,
Using his focal stimulation technique, Penfield was able to create maps of the sensory and motor cortices
of the brain. He found that the layout of these cortical representations followed the general somatotopic
relationships of the different parts of the body. Which together gave rise to a representational map of the
entire body, termed homunculus (little man).
Brain perturbations:
If damage to a brain area disrupts a cognitive function, it is likely that the damaged region is involved in
some critical way in the performance of that function. A major limitation is that the brain damage is the
result of many factors that are not under the control of the experimenter.
,Another way researchers have defined the relationship between brain damage and resulting deficits in
cognitive functions is by making restricted electrolytic or surgical lesions in animals.
Diaschisis: if one area in the brain is lesioned, other areas of the brain innervated by the damaged area
may also cease to function normally.
Pharmacological perturbations:
The first approach is to examine the influence of chronic drug use on cognitive processes. An example is
changes in reward evaluation in cocaine addicts. Cocaine activated dopamine receptors, altering the
physiology of the dopamine system, which is known to play a major role in reward evaluation.
The second approach is to administer a drug and its effects are monitored. For example: nicotine affects
neurotransmission mediated by acetylcholine, interacting with cognitive processes that include mood,
attention, memory and appetite, as well as neurological processes that can lead to addiction.
A disadvantage of administering drugs is the relative lack of specificity of their effects.
Agonists: drugs that bind to and activate receptors
Antagonists: drugs that bind to and block receptors
Computerized tomography (CT): uses a movable X-ray tube that is rotated around the patient’s head. A CT
scan gathers intensity information.
Magnetic reseonance imaging (MRI): using magnetic fields to elicit resonance. The spatial resolution of
MR images depends on the strength of the magnetic field, the strength of the gradient coils, and the types
of images being collected. It is non-invasive, MR images are of extremely high resolution and MRI
scanners can be used to generate images that are sensitive to many different aspects of brain structure.
Diffusion tensor imaging (DTI): quantifies the relative diffusivity of the water molecules in each vocel into
directional components. White matter shows more prominent anisotropy in its diffusion, whereas the
diffusion in other brain regions tends to be isotropic.
Fractional anisotropy (FA): a scalar quantity that can be computed for each voxel to express this degree of
anisotropy. This can provide important information about the composition of the tissue within a voxel.
Connectomics: obtaining full knowledge of brain connections.
A different way of perturbating brain function is direct electrical stimulation of a specific brain region.
Moderate levels of stimulation can activate neurons and trigger behavior that suggests what a given
, population normally does. However strong stimulation tends to disrupt what a given population normally
does. Intracranial brain stimulation is highly invasive.
A far less invasive approach is transcranial magnetic stimulation (TMS). Here, a strong but transient and
rapidly changing magnetic field is generated over a region of the scalp. This induces a rapidly changing
electrical field in the underlying brain tissue, resulting in an extraneous flow of current that transiently
interacts with local neural processing.
Repetitive TMS stimulation on a cognitive function of interest can then be examined by behavioral tests
that can be administered during and after the TMS application.
Drawbacks: TMS tends to affect a relatively large area, limiting anatomical resolution; (2) transcranial
stimulation can be delivered effectively to only relatively superficial brain regions; (3) the technique can
result in concurrent stimulation of scalp and head muscles; (4) the stimulation entails some risk.
Another approach for performing extracranial brain stimulation is transcranial direct current stimulation
(tDCS). Here, a constant, low-amplitude, electrical current is applied directly to the scalp.
Anodal stimulation is thought to increase the cortical excitability of the area being stimulated
Cathodal stimulation is thought to decrease the excitability.
The main disadvantage of tDCS include the spatial coarseness of the stimulation and the limited
understanding of its mechanisms.
Optogenetics: technique for selectively stimulating neural circuits far more specifically. This combines
genetics with the use of laser light to activate specific neural circuits or neuronal cell types in a variety of
experimental settings. Thus, it has both high neuronal selectivity and high temporal resolution. The basic
principle of optogenetics involves incorporating ion channels in response to light.
Genetic material that codes for the manufacture of photoreactive ion channels is extracted from light-
sensitive algae and inserted into a virus.
Measuring neural activity during cognitive processing:
Single-neuron electrical recording: measuring the action potentials produced by individual neurons.
Extracellular recording is done with fine tungsten or steel electrodes that are inserted into the
extracellular space in the cerebral cortex or deeper brain structures. For intracellular recording,
electrolyte-filled glass electrodes with a much finer tip are used.
Although single unit data can be analyzed in many ways, there are two common ways:
The neuronal firing patter across time in response to the stimulus is acquired in the form of a
peristimulus time histogram (PSTH). The neuron’s responsiveness to the stimulus is determined
by temporally aligning the responses following each of the trials and then summing the number
of action potentials across trials into a histogram time-locked to the stimulus. Such an approach
averages out random background firing.
Neuronal tuning curves: a stimulus is varied along a particular dimension and the strength of the
response is plotted as a function of the stimulus parameter being varied. The resulting curve
defines the selective sensitivity of the cell to some values of that stimulus relative to others.
Electroencephalography (EEG):
EEG recordings measure electrical brain waves that can be detected at the scalp. The EEG signal derives
from the summed dendritic field potentials of groups of neurons that are varying together.
Local field potentials (LFP’s): slower-frequency dendritic field fluctuations. They reflect more of the
integrative [processing of these large cortical neurons, rather than the output firing of the cell.
The signals are typically analyzed in term of the power in various frequency bands at each electrode.
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