PSYC 30043 Cognitive Psychology | Cognitive Neuroscience

October 2021
Levels of analysis refers to the idea that a topic can be studied in a neurons, made it possible for Cajal to clearly see that the
number of different ways, with each approach contributing its own nerve net was not continuous but was instead made up of
dimension to our understanding individual units (called neuron—basic building blocks of
the brain) connected together
Neurons: Basic Principles
 Neuron was the centerpiece of neuron doctrine—the idea
- to understand the relation between the brain and the mind—and that individual cells transmit signals in the nervous system,
specifically to understand the physiological basis for and that these cells are not continuous with other cells as
everything we perceive, remember, and think—it is necessary proposed by nerve net theory
to look within the brain and observe the small units called
Basic Parts of Neuron
neurons that create and transmit information about what
we experience and know  cell body is the metabolic center of the neuron; it contains
mechanisms to keep the cell alive
Early Conceptions of Neurons
 dendrites that branch out from the cell body is to receive
- nerve net: network, provided a complex pathway for signals from other neurons
conducting signals uninterrupted  Axons (also called nerve fibers) are usually long processes
- One reason for describing the microstructure of the brain as a that transmit signals to other neurons
continuously interconnected network was that the staining
techniques and microscopes used during that period could Conclusions About Neurons
not resolve small details, and without these details the nerve  There is a small gap between the end of a neuron’s axon
net appeared to be continuous and the dendrites or cell body of another neuron called
- Camillo Golgi developed a staining technique in which a thin synapse.
slice of brain tissue was immersed in a solution of silver nitrate  Neurons are not connected indiscriminately to other
 fewer than 1 percent of the cells were stained, so they stood neurons but form connections only to specific neurons and
out from the rest of the tissue form neural circuits.
- Spanish physiologist Ramon y Cajal using two techniques to  There are also neurons that are specialized to pick up
investigate the nature of the nerve net: information from the environment, such as the neurons in
1. he used the Golgi stain, which stained only some of the the eye, ear, and skin called receptors.
cells in a slice of brain tissue
2. he decided to study tissue from the brains of newborn The Signals That Travel in Neurons
animals, because the density of cells in the newborn brain
is small compared with the density in the adult brain
 This property of the newborn brain, combined with the fact
that the Golgi stain affects less than 1 percent of the
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Cajal knew that these neurons transmitted signals. However,  ideal for sending signals over a distance, because it means
determining the exact nature of these signals had to await the that once an action potential is started at one end of an
development of electronic amplifiers that were powerful enough to axon, the signal will still be the same size when it reaches
make the extremely small electrical signals generated by the neuron the other end
visible. - neurotransmitter: chemical released when the signals reach
the synapse at the end of the axon
- In 1920s, Edgar Adrian was able to record electrical signals
 makes it possible for the signal to be transmitted across the
from single sensory neurons
gap that separates the end of the axon from the dendrite or
 Using microelectrodes—small shafts of hollow glass filled
cell body of another neuron
with a conductive salt solution that can pick up electrical
signals at the electrode tip and conduct these signals back our main interest is not in how axons transmit signals, but in how
to a recording device these signals contribute to the operation of the mind
o recording electrode, shown with its recording tip
- Adrian did a series of experiments to relate nerve signals to
inside the neuron
stimuli in the environment and therefore to people’s experience
o reference electrode, located some distance away so
 studied the relation between nerve firing and sensory
it is not affected by the electrical signals experience by measuring how the firing of a neuron from a
- When the axon, or nerve fiber, is at rest, the meter records a receptor in the skin changed as he applied more pressure to
difference in potential between the tips of the two electrodes of the skin
-70 millivolts known as resting potential  the shape and height of the action potential remained
 neuron has a charge that is 70 mV more negative than the the same as he increased the pressure, but the rate of nerve
outside firing—that is, the number of action potentials that traveled
- when the neuron’s receptor is stimulated so that a nerve down the axon per second—increased
impulse is transmitted down the axon  if nerve impulses “are crowded closely together the
 As the impulse passes the recording electrode, the charge sensation is intense, if they are separated by long intervals
inside the axon rises to +40 millivolts, compared to the the sensation is correspondingly feeble”
outside.  electrical signals are representing the intensity of the
 As the impulse continues past the electrode, the charge stimulus, so pressure that generates “crowded” electrical
inside the fiber reverses course and starts becoming signals feels stronger than pressure that generates signals
negative again until it returns to the resting potential separated by long intervals
 This impulse, which is called the action potential, lasts - Thus, the rate of neural firing is related to the intensity of
about 1 millisecond stimulation, which, in turn, is related to the magnitude of an
- each action potential travels all the way down the axon without experience
changing its height or shape
how is the quality of experience represented in neural firing?
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- For the senses, quality across the senses refers to the different Feature Detectors
experience associated with each of the senses—perceiving light
- One possible answer to the question “how can nerve impulses
for vision, sound for hearing, smells for olfaction, and so on.
stand for different qualities?” is that perhaps there are
- We can also ask about quality within a particular sense, such
neurons that fire only to specific qualities of stimuli.
as for vision: color, movement, an object’s shape, or the
- David Hubel and Thorsten Wiesel presented visual stimuli to
identity of a person’s face.
cats and determined which stimuli caused specific neurons to
- different qualities of stimuli, and also different aspects of
fire
experience, activate different neurons and areas in the
 each neuron in the visual area of the cortex responded to a
brain
specific type of stimulation presented to a small area of the
Representation by Neural Firing retina—called these neurons feature detectors because
they responded to specific stimulus features such as
- principle of neural representation states that everything a
orientation, movement, and length
person experiences is based on representations in the person’s
- The idea that feature detectors are linked to perception was
nervous system
supported by many different experiment
The Story of Neural Representation and Cognition: A Preview - One of these experiments involved a phenomenon called
experience-dependent plasticity, in which the structure of the
- In the 1960s, researchers began focusing on recording from brain is changed by experience
single neurons in the primary visual receiving area, the place  (Collin Blakemore and Graham Cooper) kitten’s brains
where signals from the eye first reach the cortex revealed that the visual cortex had been reshaped so it
- But as research progressed, researchers began recording from contained neurons that responded mainly to verticals and
neurons in areas outside the primary visual area and discovered had no neurons that responded to horizontals
two key facts:  the kittens’ brains had been shaped to respond best to the
1. Many neurons at higher levels of the visual system fire to environment to which they had been exposed
complex stimuli like geometrical patterns and faces - This result supports the idea that perception is determined by
2. a specific stimulus causes neural firing that is distributed neurons that fire to specific qualities of a stimulus (orientation,
across many areas of the cortex in this case).
- As it became clear that understanding neural representation - This knowledge that neurons in the visual system fire to
involves casting a wide net across the brain, many researchers specific types of stimuli led to the idea that each of the
began considering the way different areas are connected to one thousands of neurons that fire when we look at a tree fire to
another. The idea of neural signals transmitted between many different features of the tree
destinations in an interconnected brain has led to today’s - it is important to realize that the visual cortex is an early stage
conception of the brain as containing a vast highway system of visual processing, and that vision depends on signals that are
that can be described in terms of “neural networks” sent from the visual cortex to other areas of the brain
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- other researchers who began exploring these “higher” levels of - neurons in the visual cortex that respond to relatively simple
the visual pathway discovered neurons that respond to stimuli stimuli send their axons to higher levels of the visual system,
more complex than oriented line where signals from many neurons combine and interact;
neurons at this higher level, which respond to more complex
Neurons That Respond to Complex Stimuli
stimuli such as geometrical objects, then send signals to even
- How are complex stimuli represented by the firing of neurons higher areas, combining and interacting further and creating
in the brain? neurons that respond to even more complex stimuli such as
- Gross’s research team presented a variety of different stimuli to faces—progression from lower to higher areas of the brain is
anesthetized monkeys. called hierarchical processing
 The discovery that neurons in the temporal lobe respond to
Sensory Coding
complex stimuli came a few days into one of their
experiments, when they had found a neuron that refused to - Sensory coding refers to how neurons represent various
respond to any of the standard stimuli, like oriented lines or characteristics of the environment
circles or squares.  problem of neural representation for the senses has been
 Nothing worked, until one of the experimenters pointed at called the problem of sensory coding
something in the room, casting a shadow of his hand on the - Specificity coding: idea that an object could be represented by
screen. the firing of a specialized neuron that responds only to that
 When this hand shadow caused a burst of firing, the object
experimenters knew they were on to something and began  straightforward, but it is unlikely to be correct
testing the neuron with a variety of stimuli, including  alternative to the idea of specificity coding is that a number
cutouts of a monkey’s hand. of neurons are involved in representing an object
 After a great deal of testing, they determined that this - Population coding: the representation of a particular object by
neuron responded best to a handlike shape with fingers the pattern of firing of a large number of neurons
pointing up. After expanding the types of stimuli presented,  advantage of population coding is that a large number of
they also found some neurons that responded best to faces. stimuli can be represented, because large groups of neurons
 researchers extended these results and provided many can create a huge number of different patterns
examples of neurons that respond to faces but don’t - Sparse coding: occurs when a particular object is represented
respond to other types of stimuli by a pattern of firing of only a small group of neurons, with the
- We saw that neurons in the visual cortex respond to simple majority of neurons remaining silent.
stimuli like oriented bars, neurons in the temporal lobe - neurons were discovered when recording from the temporal
respond to complex geometrical stimuli, and neurons in lobe of patients undergoing brain surgery for epilepsy—These
another area of the temporal lobe respond to faces. neurons responded to very specific stimuli.
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- There is also other evidence that the code for representing - Paul Broca published work based on his study of patients who
objects in the visual system, tones in the auditory system, and had suffered brain damage due to strokes that caused disruption
odors in the olfactory system may involve the pattern of of the blood supply to the brain
activity across a relatively small number of neurons, as sparse  These strokes caused damage to an area in the frontal lobe
coding suggests that came to be called Broca’s area
- Memories are also represented by the firing of neurons, but  Their speech was slow, ungrammatical, and labored and
there is a difference between representation of perceptions and often had jumbled sentence structure—diagnosed as having
representation of memories. Broca’s aphasia
 neural firing associated with experiencing a perception is - Carl Wernicke (1879) described a number of patients who had
associated with what is happening as a stimulus is present damage to an area in their temporal lobe that came to be called
 Firing associated with memory is associated with Wernicke’s area
information about the past that has been stored in the brain  Wernicke’s patients produced speech that was fluent and
o the basic principles of population and sparse coding grammatically correct but tended to be incoherent—
also operate for memory, with specific memories diagnosed with Wernicke’s aphasia
being represented by particular patterns of stored  Patients such as this not only produce meaningless speech
information that result in a particular pattern of but are unable to understand other people’s speech.
nerve firing when we experience the memory Their primary problem is their inability to match words
with their meanings, with the defining characteristic of
Localized Representation Wernicke’s aphasia being the absence of normal
- localization of function—specific functions are served by grammar
specific areas of the brain Broca’s and Wernicke’s observations showed that different aspects of
- Many cognitive functions are served by the cerebral cortex, language—production of language and comprehension of language—
which is a layer of tissue about 3 mm thick that covers the were served by different areas in the brain.
brain
- Other functions are served by subcortical areas that are - Studies of Japanese soldiers in the Russo-Japanese war of
located below the cortex 1904–1905 and Allied soldiers in World War I showed that
- Early evidence for localization of function came from damage to the occipital lobe of the brain, where the visual
neuropsychology—the study of the behavior of people with cortex is located resulted in blindness, and that there was a
brain damage. connection between the area of the occipital lobe that was
damaged and the place in visual space where the person was
Localization Determined by Neuropsychology blind
- cortical equipotentiality, the idea that the brain operated as an - The auditory cortex, which receives signals from the ears, is
indivisible whole as opposed to specialized areas in the upper temporal lobe and is responsible for hearing
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- The somatosensory cortex, which receives signals from the determine which areas of the brains of humans are activated by
skin, is in the parietal lobe and is responsible for perceptions different cognitions.
of touch, pressure, and pain.
Localization Demonstrated by Brain Imaging
- The frontal lobe receives signals from all of the senses and is
responsible for coordination of the senses, as well as higher - Functional magnetic resonance imaging (fMRI) takes
cognitive functions like thinking and problem solving. advantage of the fact that neural activity causes the brain to
- Another effect of brain damage on visual functioning, bring in more oxygen, which binds to hemoglobin molecules in
reported in patients who have damage to the temporal lobe on the blood
the lower-right side of the brain, is prosopagnosia—an  This added oxygen increases the magnetic properties of the
inability to recognize faces hemoglobin, so when a magnetic field is presented to the
- One of the goals of the neuropsychology research we have brain, these more highly oxygenated hemoglobin molecules
been describing is to determine whether a particular area of the respond more strongly to the magnetic field and cause an
brain is specialized to serve a particular cognitive function. increase in the fMRI signal.
 to reach more definite conclusions about the function of a  As a person engages in a cognitive task such as perceiving
particular area, it is necessary to test a number of different an image, the activity of the brain is determined recorded in
patients with damage to different brain areas in order to voxels--which are small, cube-shaped areas of the brain
demonstrate a double dissociation. about 2 or 3 mm on a side
 double dissociation occurs if damage to one area of the  It bears emphasizing that these colored areas do not appear
brain causes function A to be absent while function B is as the brain is being scanned. They are determined by a
present, and damage to another area causes function B to be procedure that involves taking into account how the brain is
absent while function A is present responding when the person is not engaged in a task and
the change in activity triggered by the task
Localization Determined by Recording from Neurons
 Complex statistical procedures are used to determine the
- Another tool for demonstrating localization of function is task-related fMRI—the change in brain activity that can
recording from single neurons. be linked specifically to the task.
- Doris Tsao and coworkers (2006) found that 97 percent of  The results of these calculations for each voxel are then
neurons within a small area in the lower part of a monkey’s displayed as colorful activation patterns
temporal lobe responded to pictures of faces but not to pictures
Looking at Pictures
of other types of objects
- The idea that our perception of faces is associated with a  A face area has also been identified by having people in a
specific area of the brain is also supported by research using brain scanner look at pictures of faces
the technique of brain imaging which makes it possible to o This area, which is called the fusiform face area
(FFA) because it is in the fusiform gyrus on the
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underside of the temporal lobe is the same part of Distributed Representation
the brain that is damaged in cases of prosopagnosia
- The explanation—that different areas respond to different
 perceiving pictures representing indoor and outdoor scenes
features of humans—illustrates a central principle of cognition:
like those shown in activates the parahippocampal place
most of our experience is multidimensional
area (PPA)
o Apparently, what is important for this area is Looking at a Face
information about spatial layout, because increased
- in addition to identifying an object as a face (“that’s a face”),
activation occurs when viewing pictures both of
we also respond to the following additional aspects of faces:
empty rooms and of rooms that are completely
1. emotional aspects (“she is smiling, so she is probably
furnished
happy,” “looking at his face makes me happy”)
 the extrastriate body area (EBA), is activated by pictures
2. where someone is looking (“she’s looking at me”)
of bodies and parts of bodies (but not by faces)
3. how parts of the face move (“I can understand him better
Looking at Movies by watching his lips move”)
4. how attractive a face is (“he has a handsome face”)
 On one hand, the results confirm the earlier research that 5. whether the face is familiar (“I remember her from
identified specific areas of the brain responsible for the somewhere”)
perception of specific types of stimuli like faces, places, - The fact that looking at a face activates many areas of the brain
and bodies. is called distributed representation
 On the other hand, these new results reveal a map that  Cognitions, be they perceptions from looking at something,
stretches over a large area of the cortex. or processes such as remembering or thinking, activate
o the area labeled “Humans” at the bottom of the numerous, sometimes widely separated, areas of the brain.
brain (which is actually on the underside of the
brain) corresponds to the fusiform face area which Remembering
responds to all aspects of faces. - there is evidence that short-term and long-term memories are
o The area labeled “Humans” higher on the brain served by different areas of the brain
responds specifically to facial expressions. - thinking about episodic and semantic memories activates
o The areas labeled “Talking” correspond to Broca’s different areas of the brain
and Wernicke’s areas. - some areas of the brain play important roles in forming new
 As we will now see, even though there is a great deal of memories and retrieving old ones, but there is also evidence
evidence for localization of function, we need to consider that remembering activates areas throughout the brain
the brain as a whole in order to understand the - Most memories are combinations of many of emotional
physiological basis of cognition. components, each of which activates different areas of the
brain
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Producing and Understanding Language 1. There are complex structural pathways called networks
that form the brain’s information highway.
- explaining the physiology of language involved more than just
2. Within these structural pathways there are functional
two separate, localized language areas
pathways that serve different functions.
- Modern researchers have shown that damage to areas outside
3. These networks operate dynamically, mirroring the
of Broca’s and Wernicke’s areas can cause problems in
dynamic nature of cognition.
producing and understanding language
4. There is a resting state of brain activity, so parts of the
- There is also evidence that nonlanguage functions are
brain are active all the time, even when there is no
associated with parts of Broca’s area and that processing of
cognitive activity.
sentence grammar occurs throughout the language system
- the language system is organized into two sets of pathways: Structural Connectivity
 one (in blue), which is involved with processing sounds,
- brain’s “wiring diagram” created by nerve axons that connect
production of speech, and saying words
different brain areas
 the other (in red), which is involved in understanding
- Early researchers determined these connections using classical
words
neuroanatomical techniques in which slices of brain tissue were
 Both sets of pathways are also involved in understanding
stained to highlight axons, which enabled them to see the
sentences
neural pathways with a microscope.
One thing that the examples of perceiving faces, remembering, and - new techniques have been developed that make more extensive
language have in common is that they involve experiences that mapping of the brain’s connections possible
activate many separated brain areas, and there is evidence that many  track-weighted imaging (TWI), is based on detection of
of these areas are linked either by direct neural connections or by how water diffuses along the length of nerve fibers
being part of a number of interconnected structures. This brings us to - Pictures of the brain’s pathways obtained by these new
an important new way of understanding the physiology of cognition techniques led to the coining of the term connectome to
that involves neural networks. indicate the “structural description of the network of
elements and connections forming the human brain”, or
Neural Networks
more simply, the “wiring diagram” of neurons in the brain
- interconnected areas of the brain that can communicate with - Determining the brain’s wiring diagram is an important step in
each other understanding how different areas of the brain communicate,
- The idea of neural networks is a logical extension of the idea of because communication depends on structural connections
distributed processing, because it makes sense that if many - maps of structural connectivity of the brain have recently
areas are involved in a particular type of cognition, that they been likened to “fingerprints” that are different for every
might be connected. person, so it could be argued that the brain’s wiring makes us
- Four Principles: who we are
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But to fully understand how the brain’s structural network makes us
who we are, or how it helps create cognition, it is necessary to
determine how groups of neurons within the connectome form
functional connections that are related to specific types of cognition.
Functional Connectivity
- How is it possible to determine what parts of a neural network
are involved in different functions?
- One way this question has been answered is by measuring
functional connectivity, with functional connectivity being
determined by the extent to which neural activity in two brain
areas are correlated - There are also other ways to determine functional connectivity.
 If the responses of two brain areas are correlated with  functional connectivity can be determined by measuring the
each other, this means that they are functionally connected task-related fMRI at the seed and test locations and
 Determined by resting-state fMRI—the fMRI response determining the correlations between the two responses, as
measured while a person is at rest as introduced by we did for resting-state fMRI.
Bharat Biswal and coworkers.  It is important to note that saying two areas are functionally
1. Use task-related fMRI to determine a brain location connected does not necessarily mean that they directly
associated with carrying out a specific task. communicate by neural pathways
2. Measure the resting-state fMRI at the seed location. - Functional connectivity and structural connectivity are not,
The resting-state fMRI of the seed location is called a therefore, the same thing, but they are related, so regions with
time-series response because it indicates how the high structural connectivity often show a high level of
response changes over time. functional connectivity
3. Measure the resting-state fMRI at another location, - the overall structural map of the brain is divided into smaller
which is called the test location. The response of the functional maps, so different cognitions activate different
test location Somatosensory, which is located in an area groups of neuron
of the brain responsible for sensing touch.
But to really understand what is happening during cognition, we need
4. Calculate the correlation between the seed- and test-
to go beyond just identifying areas that serve different functions. We
location responses. The correlation is calculated using a
need to consider the dynamics of cognition.
complex mathematical procedure that compares the
seed and test responses at a large number of places The Dynamics of Cognition
along the horizontal time axis.
- the flow of activity within and across the functional networks
in the brain also changes, depending on conditions
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- even a simple everyday experience like looking at and picking  mind wandering decreases performance on tasks that
up a cup of coffee involves rapid switching and sharing of require focused attention
information between a number of different functional networks
- changes in connectivity can also occur more slowly
- Functional networks are not, therefore, simply static diagrams
but involve constantly changing activity within and across
networks
- if functions are represented by structures in many different
areas of the brain, it makes sense that they would be able to
communicate with each other.
A network was discovered that responded not when people were
engaged in tasks—but when they weren’t! This network is called the
default mode network.
The Default Mode Network
- default mode network (DMN) is a network of structures that
respond when a person is not involved in specific tasks
- Gordon Shulman and coworkers (1997), who noted a few
earlier fMRI studies in which presentation of a task caused a
decrease in activity in some areas of the brain, and stopping
the task caused an increase in activity in the same areas.
- Marcus Raichle and coworkers (2001), in a paper titled “A
Default Mode of Brain Function,” proposed that the areas that
decrease activity during tasks represent a “default mode” of
brain function—that is, a mode of brain function that occurs
when it is at rest.
- research using the resting-state functional connectivity method
indicated that areas in the frontal and parietal lobes that
decrease activity during tasks have correlated resting state
activity
 These areas are, therefore, part of a functional network,
which is identified as the default mode network (DMN)
- when the DMN is active, people’s minds tend to wander