Association Cortices

Question 1

What are the association cortices?

Answer 1

All the neocortex in human and non-human primate brains which is the sensory and motor areas

include most of the cerebral surface and are largely responsible for the complex processing between the arrival of input in the primary sensory cortices and the generation of behavior.

Question 2

How many layers of the neocortex are there?

Answer 2

6 layers, also called laminae, which are based on differences in cell density

Question 3

Why are there different layers of the neocortex?

Answer 3

Different layers allows you to process information by having different inputs to different layers, and outputs in different layers

This allows higher-order brain functions such as sensory perception, cognition, generation of motor commands, spatial reasoning and language.

Question 4

How did Brodmann’s find layers of the neocortex?

Answer 4

Much knowledge about the cerebral cortex is based on descriptions of differences in cell number and density throughout the cortical mantle.

Nerve cell bodies are rich in basophilic substances (RNA, eg ) and stain darkly with reagents such as cresyl violet acetate.

These Nisslstains provide a picture of brain structure at the histological level.

The most striking feature revealed in this way is the distinctive lamination of the cortex in humans and other mammals.
Humans have three to six cortical layers, depending on the area of cortex.
These layers, or laminae, are designated with the numerals 1–6 .
Laminar subdivisions are indicated with letters

Each of the cortical laminae in the neocortex has characteristic functional and anatomical features

Brodmann= analysis of brain regions distinguished in this way, describing some 50 distinct corticalregions, or cytoarchitectonic area

Question 5

What are Brodmann’s areas? Based on the layers

Answer 5

The Brodmann areas are a way of mapping the cortex and its distinguished functions.
Through using Brodmann’s areas, the cortex of the brain can be divided into 52 areas which are numbered sequentially.
Areas can be distinguished by microscopic anatomy through the shapes and types of cells and their connections

A Brodmann area is a region of the cerebral cortex, in the human or other primate brain, defined by its cytoarchitecture, or histological structure and organization of cells.

Question 6

What are the major connections of the neocortex?

Answer 6

Hippocampal formation
Amygdala
Thalamus
Brainstem modulatory systems

Question 7

What enables association cortices to make associations?

Answer 7

The fact they get input from the primary and secondary sensory cortical regions, interconnected with the motor and premotor cortices and local connections with corresponding and non-corresponding cortical areas

Question 8

What are the targets of cortical output?

Answer 8

Hippocampal formation
Amygdala
Thalamus
Caudate & Putamen (striatum)
Brainstem
Spinal cord

Question 9

What is the input to the parietal cortex?

Answer 9

Parietal cortex receives information from the visual cortex and the visual system goes up into the parietal lobe and down to the temporal lobe

Question 10

Is a left or right lesion of the parietal lobe more severe?

Answer 10

Right parietal cortex mediates attention in left and right visual field whereas left parietal cortex mediates attention in the right visual field

so lesions in the right hemisphere=more severe

Question 11

What disorder is caused by lesions to the parietal cortex?

Answer 11

Contralateral neglect

A deficit in attention paid to one side of the visual field, its an inability to attend to objects, or even one’s own body, in a portion of space, despite the fact that visual acuity, somatic sensation, and motor ability remain intact.

Affected individuals fail to report, respond to, or even orient to stimuli presented to the side of the body (or visual space) opposite the lesion (contralateral to the damage)

It can result in the individual not attending to stimuli in that area to the extent that he does not seem to be aware of such stimuli.

e.g. draw half a house

Question 12

What does contralateral neglect tell us about the parietal association cortex?

Answer 12

Tells us that the parietal lobe is linked to attention, perceptual awarenss and spatial representations

Question 13

What do studies of monkeys tell us about the parietal cortex?

Answer 13

Selective activation of neurons in the monkey parietal cortex as a function of attention.

Rhesus monkey’s attention is directed to a light associated with a fruit juice reward.

Although the baseline level of activity of the neuron being studied here remains unchanged when the monkey ignores a visual target ,firing rate increases dramatically when the monkey attends to the same stimulus.

When given a choice of where to attend, the monkey pays increasing attention to a particular visual target when more fruit juice reward can be expected for doing so, and the firing rate of the parietal neuron under study increases accordingly

These findings indicate the neurons in the parietal cortex play an important role in attention

Question 14

What do lesions tell us about the temporal association lobe?

Answer 14

major functions are the recognition and identification of stimuli that are attended to, particularly complex stimuli.

Damage = uable to recognise/ name/ identify different categories of objects.

Question 15

What are different aspects of agnosias?

Answer 15

Lexical aspect (a mismatching of verbal/cognitive symbols with sensory stimuli)

Mnemonic aspect (a failure to recall stimuli when confronted with them again)

Question 16

What is propagnosia?

Answer 16

The main type of agnosia

Inability to identify/recognise familiar individuals by their facial characteristics

In some cases cannot recognize a face at all including their own (autopropagnosia).

BUT
Such individuals are aware that a visual stimulus is present and can describe aspects or elements of it without difficulty.

E.g. L.H.
Couldn’t recognize familiar faces, report that they were familiar, or answer questions about faces from memory.
He could identify common objects, discriminate subtle shape differences, and recognize the sex, age, and the“likeability” of faces. Moreover, he could identify particular people by non-facial cues such as voice, body shape, and gait.

Question 17

What is the result of lesionsin the temporal lobe?

Answer 17

Lesions of the right temporal cortex= agnosia for faces and objects

Lesions of the corresponding left temporal cortex = difficulties with language-related material.

The lesions that cause recognition deficits, particularly for faces= in the inferior temporal cortex, or near the fusiform gyrus

Those that cause language-related problems in the left temporal lobe= on the lateral surface of the cortex.

Question 18

What do brain lesions tell us about the frontal lobe association cortex?

Answer 18

An individual’s “personality”
Appreciation of self in relation to the world
Allows behaviors to be planned and executed normally

Lesion = difficulty carrying out complex behaviors that are appropriate to circumstances
+ Unable to match ongoing behavior to present/future demands

The frontal cortex integrates complex information from sensory and motor cortices, as well as from the parietal and temporal association cortices.

e.g Phineas Gage
implicated personality in temporal lobe -> became inconsiderate and agressive + could no longer cope with normal social intercourse or the kind of practical planning

Question 19

Other than personality, what do frontal lobe lesions impair?

Answer 19

That the frontal cortex has more functions than any other neocortical regions so deficits are diverse, particularly if both hemispheres are involved.

Brain lesions in the frontal lobe affect performance in the Wisconsin card sorting task (work out the rule of organising cards)

Also affects the Tower of Hanoi (move all the disks over to Tower 3 but you cannot place a larger disk onto a smaller disk)

Frontal lobe lesions cause problems with impaired restraint, disordered thought, perseveration and the inability to plan appropriate action

Question 20

What is the delay response task?

Answer 20

The monkey watches an experimenter place a food morsel in one of two wells and both wells are then covered. A screen is then lowered for an interval of a few seconds to several minutes (the delay).
When the screen is raised, the monkey gets only one chance to uncover the well containing food and retrieve the reward.

Thus, the animal must decide that it wants the food, remember where it is placed, recall that the cover must be removed to obtain the food, and keep all this information available during the delay so that it can be used to get the reward

The monkeys ability to carry out this STM task is abolished when the prefrontal cortex is destroyed bilaterally
-> this result aligns with clinical findings in human patients

Question 21

What does the delay response task in monkey tell us about the frontal association cortices?

Answer 21

Tells us that there are neurons that appear to be specifically involved in planning which have been identified in the frontal cortices of rhesus monkeys

Question 22

What is the role of neurons in the delay response task?

Answer 22

Some neurons in the prefrontal cortex, (particularly principal sulcus) =activated when monkeys perform computerized variants of the delayed response task,

Maximally active during the delay -> firing represented info about the location of the food maintained from the presentation part of the trial -> the cognitive information needed to guide behavior when the screen is raised

Such neurons return to a low level of activity during the actual motor phase of the task, suggesting that they represent short-term memory and planning

Question 23

What do combined findings from Phineas Gage and the Delay response task in monkeys tell us about the frontal lobe?

Answer 23

These observations endorse the notion, first inferred from studies of brain-damaged individuals such as Phineas Gage, that the frontal lobe contributes specifically to the cognitive functions that use remembered information to plan and guide appropriate sequences of behaviour

Question 24

What are Jennifer Aniston Neurons?

Answer 24

The “Jennifer Aniston neuron”, is a hypothetical neuron that represents a complex but specific concept or object. It activates when a person “sees, hears, or otherwise sensibly discriminates” a specific entity, such as their grandmother.

These neurons are in the medial temporal lobes.