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Samenvatting The Student's Guide to Cognitive Neuroscience - Jamie Ward
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Samenvatting The Student's Guide to Cognitive Neuroscience - Jamie Ward - 20-10-15 22:Chapter 1: Introducing cognitive neuroscience
History
Cognition —> variety off higher mental processes such as thinking, perceiving, imagining, speaking, acting and
planning. Cognitive neuroscience is a bridging discipline between cognitive science and cognitive psychology, on the one
hand, and biology and neuroscience, on the other. Study brain in laboratory.
Mind-body problem (mind-brain problem) —> how can physical substance give rise to our sensations, thought and
emotions?
Dualism (Descartes)—> mind and brain are made up of different kinds of substances, even though they may
interact. —> Mind = non-physical and immortal, body is physical and mortal.
Spinoza —> mind and brain are two different levels of explanations of the same thing, not two different kind of
things. —> Dual-aspect theory.
Reductionism —> although cognitive, mind-based concepts (emotions, memories, attention) are currently useful for
scientific exploration, they will eventually be replaced by purely biological constructs (patterns of neuronal firings,
neurotransmitter release). —> Psychology will eventually reduce to biology.
Those who favor dual-aspect theory over reductionism point out that an emotion will still feel like an emotion even if we were to fully
understand its neural basis, and, as such, the usefulness of cognitive, mind-based concepts will never be fully replaced.
Scientific approaches to mind and brain
Aristotle —> cognition was part of the heart, not the brain.
Phrenology (Gall & Spurzheim, 19th century) —> two key assumptions:
1) different regions of the brain perform different functions and are associated with different behaviors
2) the size of these regions produces distortions of the skull and correlates with the individual differences in
cognition and personality.
—> The notion of functional specialization within the brain has effectively endured into modern cognitive
neuroscience. —> Different regions of the brain are specialized for different functions.
However —> skull shape has nothing to do with cognitive function. But the basic idea of functional specialization
paved the way for future developments. Broca (1861) —> language could be localized to a particular region of the brain.
Lichtheim, Wernicke —> brain damage can lead to poor speech comprehension and good procession, or good
speech comprehension and poor production —> empirical observations were being used to determine what the building
blocks of cognition are, rather than listing them from first principles. Second, they were developing models of cognition
that did not make direct reference to the brain. —> The approach of using patients with acquired brain damage to inform
theories of normal cognition is called cognitive neuropsychology and remain influential today.
Freud & James —> took mind away from its biological underpinnings —> topics like consciousness, attention and
personality. Neuroscience has nothing to say about that until quite recently. Another reason for schism between
psychology and biology —> one can develop coherent and testable theories of cognition that do not make claims about
the brain. —> Modern foundations of cognitive psychology lie in the computer metaphor of the brain and the
information processing approach (1950s) —> behavior is described in terms of a sequence of cognitive stages:
perceptual processes occur, followed by attentional processes that transfer information to short-term memory and thence
to long-term memory (Broadbent).
Computer idea develops —> many cognitive models contain some element of interactivity and parallel processing —
> Interactivity: the fact that stages in processing may not be strictly separate and that later stages can begin before
earlier stages are complete ==> later stages can influence the outcome of early ones (top-down processing). Parallel
processing refers to the fact that lots of different information can be pressed simultaneously.
1980s —> computers powerful —> calculating sets of outputs and give a set of inputs. Neural network:
computational models in which information processing occurs using many interconnected nodes.
Connectionist models —> architectural features. —> They are composed of arrays of simple-information-carrying
units called nodes (the basic unit of neural network that are activated in response to activity in other parts of the
network). They respond to a particular set of inputs (letters, certain sounds etc) and proceed a restricted set of outputs.
It is possible to calculate, mathematically, what the output of any node would be, given a set of input activations and a set
of weights.
The birth of cognitive neuroscience
Imaging technology provided driving force for modern-day cognitive neuroscience. Rachel (1998)
Present-day neuroscience —> broad diversity of methods —> the distinction between recording methods and
stimulation methods is crucial in cognitive neuroscience. Direct electrical stimulation of the brain in humans is now
rarely carried out. Modern-day equivalent —> stimulation across the skull rather than directly to the brain (i.e.
, Samenvatting The Student's Guide to Cognitive Neuroscience - Jamie Ward - 20-10-15 22:
transcaranially), includes:
1) transcranial magnetic stimulation (TMS)
2) transcranial direct currents stimulation (tDCS)
Electrophysiological methods (EEG/ERP and single-cell recordings) and magneto physiological methods (MEG)
record the electrical and magnetic properties of neurons themselves (Chapter 3). In contrast, functional imaging methods
(PET and fMRI) record physiological changes associated with blood supply to the brain, which evolve more slowly over
time —> hemodynamic methods (Chapter 4.)
The methods of cognitive neuroscience can be placed on a number of dimensions:
1) temporal resolution —> the accuracy with which one can measure when an event (e.g. a physiological
change) is occurring. The effects of brain damage are permanent and so this has no temporal resolution as such. EEG,
MEG, TMS and single-cell recording have millisecond resolution. FMRI has a temporal resolution of several seconds
that reflects slower hemodynamic response.
2) the spatial resolution —> the accuracy with which one can measure where an event (e.g. a physiological
change) is occurring. Lesion and functional imagine methods have comparable resolution at the millimeter level, whereas
single-cell recordings have spatial resolution at the level of the neuron.
3) the invasiveness of a method refers to whether the equipment is located internally or externally. PET is
invasive because it requires an injection of a radio-labeled isotope. Single-cell recordings are performed on the brain
itself and are normally only carried out in non-human animals.
Does cognitive psychology need the brain?
The claim is not that cognitive neuroscience is replacing cognitive psychology, but merely yay cognitive
psychological theories van inform theories and experiments in the neurosciences and vice versa.
Computer analogy —> one can learn about the information processing (software) without knowing about the brain
(hardware). However, information processing is not written by some third person and then inscribed into the brain.
Rather, the brain provides causal constraints on the nature of information processing —> is not analogous to the
computer domain in which the link between software and hardware is arbitrarily determined by a computer programmer.
Does neuroscience need cognitive psychology?
In the brain, one does not see memories, thought, perceptions etc (stuff of cognitive psychology), but gray matter,
white matter, blood vessels etc (the stuff of neuroscience). It is the latter, not the former, that one observes when
conducting a functional imaging experiment. Developing a framework for linking the two will necessarily entail dealing
with the mind-body problem either tacitly of explicitly. This is a daunting challenge. Functional imaging has real
scientific grounding, in respect to phrenology. The question of whether cognitive, mind-based concepts will eventually
become redundant (under a reduciontists account) or coexist with neural-based accounts (eg as in dual-aspect theory) is
for the future to decide. For now, cognitive, mind-based concepts have an essential role to play in cognitive neuroscience.
Is the brain modular?
Modularity —> the notion that certain cognitive processes (or regions of the brain) are restricted in the type of
information they process). Fodor —> 2 different classes of cognitive process: central systems and modules. The
difference —> relates to the types of information they can process, modules are held to demonstrate domain specificity —
> they process only one particular type of information (color, shape, words, faces etc). Central sestinas are held to be
domain independent in that the type of information processed is non-specific (candidates would be memory, attention,
executive functions etc). According to Fodor, one advantage of modular system is that, by processing only a limited type
of information, they can operate rapidly, efficiently and in isolation from other cognitive systems. An additional claim is
that modules may be innately specified in the genetic code.
Summary:
- The mind-body problem refers to the question of how physical matter (the brain) can produce mental experiences,
and this remains an enduring issue in cognitive neuroscience.
- To some extent, the different regions of the brain are specialized for different functions.
- Functional neuroimaging has provided the driving force for much of the development of cognitive neuroscience,
but there is a danger in merely using these methods to localize cognitive functions without understanding how they
work.
- Cognitive psychology has developed as a discipline without making explicit references to the brain. However,
biological measures can provide an alternative source of evidence to inform cognitive theory and the brain must provide
constraining factors on the nature and development of the information-processing models of cognitive science.
Chapter 2: Introducing the brain
, Samenvatting The Student's Guide to Cognitive Neuroscience - Jamie Ward - 20-10-15 22:
Neurons
All neurons have the same structure more or less —> 3 components:
1) cell body (soma) —> genetic code, neurotransmitters
2) dendrites —> receive information
3) axon —> sends information
—> Differences in the types of neurons in terms of the spatial arrangements of the dendrites and axon.
Cell body —> nucleus and other organelles. Nucleus: genetic code (certain neurotransmitters).
Neurons receive information from other neurons and they make a “decision” about this information (by changing
their own activity) —> passing them on to other neurons.
Dendrites —> receive information from other neurons in close proximity.
Axon —> sends information to other neurons.
Each neuron has many dendrites, but only one axon. (The axon can be divided into several branches, called
collaterals)
Terminal of axon flattens into a disc-shaped structure —> chemical signals enable communication between a small
gap —> synapse: the small gap between neurons in which neurotransmitters are released, permitting signaling between
neurons. The two neurons forming the synapse: presynaptic and postsynaptic —> reflecting the direction of information
flow (from axon to dendrite).
When a presynaptic neuron is active, an electrical current (action potential = a sudden change, depolarization and
depolarization, in the electrical properties of the neuron membrane in an axon) is propagated down the length of the
axon. —> When action potential reaches the axon terminal, chemicals are released into the synaptic cleft —> these
chemicals are neurotransmitters (a small portion of synapses, such as retinal gap junctions, signal electrically and not
chemically). Neurotransmitters bind to receptors on the dendrites or cell body of the postsynaptic neuron and create a
synaptic potential. This is conducted passively (without creating an action potential) through the dendrites and soma of
the postsynaptic neuron. Is they are strong enough when they reach the beginning of the axon in the postsynaptic
neuron, an action potential (an active electrical current) will be triggered in this neuron. —> Each postsynaptic neuron
sums together many synaptic potentials, which are generated at many different and distant dendritic sites (in contrast to
a simple chain reaction). Passive conduction tends to be short ranged —> electrical signal is impeded by the resistance of
the surrounding matter. Active conduction enables long-range signaling between neurons by the propagation of action
potentials.
Electrical signaling and the action potential
Each neuron —> surrounded by a cell membrane that acts as a barrier to the passage of certain chemicals. —>
Certain molecules act as gatekeepers and allow particular chemicals in and out under certain conditions —> charged
sodium (Na+) and potassium (K+) ions. The balance between these ions on the inside and outside of the membrane is
such that there is normally a resting potential of -70mV across the membrane (the inside being negative relative to the
outside).
Voltage-gated io channels are importent in the generation of an action potential. They are found only in axons —>
that’s why only the axon is capable of producing action potentials. Sequence =
1) if a passive current that is strong enough flows across the axon membrane, it begins to open the voltage-gated Na
+ channels.
2) when channel is open —> Na+ may enter the cell and the negative potential normally found on the inside is
reduced. At -50mV the cell membrane becomes completely permeable and the charge on the inside of the cell
momentarily reverses. This sudden depolarization and subsequent depolarization in electrical charge across the
membrane is the action potential.
3) the negative potential of the cell is restored via the outward flow of K+ through voltage-gated K+ channels and
closing of the voltage-gated Na+ channels.
4) there is a brief period in which hyper polarization occurs (the inside is more negative than at rest). This makes it
more difficult for the axon to depolarize straight away and prevents the action potential from traveling backwards.
An action potential in 1 part of the axon opens adjacent voltage-sensitive Na+ channels —> the action potential
moves down the length of the axon, starting from the cell body and ending at the axon terminal. The conduction of the
action potential along the axon can be speeded up if the axon is myelinated. Myelin = a fatty substance that is deposited
around the axon of some neurons that speeds conduction. It blocks the normal Na+/K+ transfer and so the action
potential jumps, via passive conduction, down the length of the axon at the point at which the myelin is absent )called
nodes of Ranvier). Destruction of myelin is found in a number of pathologies —> MS.
Chemical signaling and the postsynaptic neuron
When action potential reaches the axon terminal —> electrical signal initiates a sequence of events leading to the
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