Cognitive functions and organization of the cerebral cortex

Question 1

What is cognition?

Answer 1

Anything that happens ‘in-between’.
ex: memory, learning, attention, executive functions, and consciousness.
Information at this level is complex and multi-dimensional.

Question 2

What is the cortex?

Answer 2

A wrinkled two-dimensional sheet of layered neurons.

Question 3

Why isn’t the cortex flat?

Answer 3

The wrinkles allow the cortex to keep a 2D topographical map while increasing the available surface area to increase processing power.

Question 4

What are the sensory cortices?

Answer 4

Primary and secondary auditory, visual, somatosensory, gustatory, and olfactory cortices.

Question 5

What are the motor cortices?

Answer 5

Primary motor cortex, premotor cortex, and the secondary motor cortex or the supplementary motor cortex.

Question 6

What is an association cortex?

Answer 6

Regions of the cortex where an injury causes cognitive deficits that cannot be
explained by impairment of sensory or motor function alone.

Question 7

What are the association cortices?

Answer 7

Temporal association cortex, Parietal association cortex, Frontal association cortex, Limbic association cortex.

Question 8

What are the inputs to association cortices?

Answer 8

Primary and secondary sensory cortices, motor cortices, brainstem, thalamus, and hippocampus.

Question 9

Where do association cortices output to?

Answer 9

Hippocampus, basal ganglia, cerebellum, thalamus, and other cortical areas.

Question 10

What are the differences between primary sensory areas and higher order sensory areas?

Answer 10

1. Primary sensory areas have a high precision map of the sensory receptor surface while the higher-order sensory areas have much less precise maps of the array of peripheral sensory receptors.
2. Primary sensory areas receive input from the thalamic sensory relay while higher-order sensory areas receive input from other thalamic nuclei and lower-order sensory areas of the cortex.
3. Primary sensory areas have a small receptive field compared to the higher-order sensory areas which have a larger receptive field.
4. Injury in the primary sensory areas results in simple sensory loss while injury in the higher-order sensory areas results in deficits of perception and cognition with intact detection of sensory stimuli.
5. Primary sensory areas have limited connection to other cortical areas, only nearby areas of the same modality, while higher-order sensory areas have connections to nearby unmodal areas & distal areas in frontal and limbic lobes.

Question 11

What are some functions of information flow in the nervous system?

Answer 11

1. Sensory information is processed serially.
2. Each area carries certain computations and conveys
   them to the next area, going higher in complexity
   and in abstraction of representation.
3. Higher-order areas project back to the lower-order
   areas from which they receive input.
4. Parallel pathways in each modality lead to dorsal and
   ventral association areas.
5. Goal directed motor behavior is controlled in the
   frontal lobe.

Question 12

What are the principals of Organization of functional areas in the cortex?

Answer 12

1) all areas fall into a few functional
categories
2) areas in a category occupy a discrete,
continuous portion of the cortical sheet
3) areas that are functionally related
occupy neighboring sites

Question 13

How many layers are in each kind of major cortex in the brain?

Answer 13

Paleocortex (ex. Pyriform cortex, in the temporal lobe): 3 layers
Neocortex (ex. motor cortex, in the parietal lobe): 6 layers
Archicortex (ex. hippocampus, in the temporal lobe) 4 layers

Question 14

What separates the layers in the cortices?

Answer 14

Cell morphology, type and density.

Question 15

What are the features of a canonical circuit in a cortical structure?

Answer 15

• Each layer has a primary source of inputs and a primary output target
• Connections in the vertical axis (columnar or radial connections)
• Connections in the horizontal axis (lateral or horizontal)
• Cells with similar functions arranged in radially aligned groups
• Interneurons within layers give rise to axons that extend horizontally (linking functionally similar groups)

Question 16

How did we learn that that cytoarchitectonically different regions were also functionally distinct?

Answer 16

Through work from (1) neurological cases (2) in-vivo electrophysiology in animals and (3) neurosurgical patients.

Question 17

What are the thalamic nuclei that are specialized to association cortices?

Answer 17

Pulvinar - sends input to the parietal association cortices

Medial dorsal - sends input to the frontal association cortices

Question 18

What kind of input is the majority of input to association cortices?

Answer 18

The majority of input in corticocortical connections:

intrahemispheric connections: Short ‘U shaped’ association fibers for short distances and long association fibers for long distances

interhemispheric connections: Long association fibers that go through the corpus callosum.

Question 19

Where is the cholinergic nuclei located and what is it’s purpose?

Answer 19

Located in the brainstem and basal forebrain. Serves memory, learning, and attention.

Question 20

Where is the dopaminergic nuclei located and what is it’s purpose?

Answer 20

Located in the midbrain. Responsible for pleasure, salience, motivation, and reward learning.

Question 21

Where is the noradrenergic nuclei located and what is it’s purpose?

Answer 21

Located in the brainstem. Responsible for wakefulness and stress reaction.

Question 22

Where is the serotoninergic nuclei located and what is it’s purpose?

Answer 22

Located in the brainstem. Responsible for mood, memory processing, and sleep.

Question 23

What are the features of the parietal association cortex?

Answer 23

• Attention and awareness of the body and stimuli around it
• Integrates somatic, visual, acoustic and vestibular sensory information - spatial cognition and motor control of the eyes and the extremities.
• IPS - projects to the premotor area, the frontal eye fields, and prefrontal area - control of ocular movements, reaching and grasping of the upper extremities, and spatial working memory.
• Inferior parietal lobule and precuneus project to the parahippocampal and entorhinal cortices strongly associated with hippocampal functions for long-term memory formation.
• Contralateral neglect syndrome – role in spatial awareness
• Attention sensitive neurons
• Important role in multimodal/sensorimotor integration

Question 24

What are the features of the temporal association cortex?

Answer 24

• Auditory association cortices – including Wernickes (language comprehension area)
• Ventral –WHAT- pathway – recognition of sensory stimuli – faces/words/objects – deficit: AGNOSIA
• Representation of knowledge – Semantic memory - meaning
• Strong connection to the limbic system.
• Ventral/Inferior temporal surface (“What” pathway) – Agnosia – a specific type of stimuli according to region. More anterior –associative // More posterior - Apperceptive
• Anterior pole – Semantic dementia – cannot associate words with their meanings ( fluent aphasia, anomia, impaired comprehension of word meaning, and associative visual a gnosia)

Question 25

What are the features of the frontal association cortex?

Answer 25

• Largest lobe/widespread connectivity/most complex functional anatomy
• Integrates information from sensory & motor cortices and parietal & temporal association cortices.
• Appreciation of self in relation to the world – allows selection, planning, and execution of appropriate behavior (social contexts)
• Damage in the frontal lobe – change in Catani, 2019 “character“ or “personality”
• Functional deficits: Cognitive disabilities, impaired restraint, disordered thought, perseveration, and inability to plan appropriate action.

Question 26

What are the features of the limbic association cortex?

Answer 26

• It used to be understood as a unitary system “the limbic lobe” – homeostatic and instinctual drives
• Orbital and ventromedial cortex – connected to amygdala and hippocampus – emotional processes
• Hippocampal formation – mediates the formation of long-term memories and then transfers them to the neocortex.
• Other divisions – intermediaries between hipocampal formation and association cortices

Question 27

What are some caveats to the separation of functional areas of the brain?

Answer 27

1. Areas are NOT separate modules - gradient
2. They are organized into large, densely interconnected networks that function together → LARGE SCALE BRAIN NETWORKS
3. Within these NETWORKS, there is a hierarchical organization.
4. As areas go up in the hierarchy, information is more abstract and distant from peripheral sensors. (think primary visual cortex vs. Temporal association cortices)