Association Cortices Flashcards
Allocortex
Made up of paleocortex and archicortex.
Paleocortex is evolutionarily old and signified by having 3 layers. (e.g. piriform cortex)
Archicortex is also evolutionarily old and contains 3/4 layers. (e.g. hippocampus)
Different from Isocortex (neocortex) which has 6 layers.
Mesocortex
4/5 layers, thought of as a transitional zone between Allocortex and Isocortex.
Isocortex (neocortex)
6 layers, constitutes most of the human brain, including the association cortices.
Describe the common layout of the 6 layers in neocortex.
Layer 1: No neural cell bodies, only axons and dendrites
Layer 2: Input mainly from other cortical areas
Layer 3: Output mainly to other cortical areas
Layer 4: Input mainly from thalamus (Non-cortical input)
Layer 5: Output mainly to basal ganglia and spinal cord (non-cortical output)
Layer 6: Output mainly to thalamus
Input layers 2 and 4 are rich in granule cells, why they are called granular layers.
Output layers 3 and 5 are rich in pyramidal neurons, why they are called pyramidal layers.
What is the main function of layer 2/3?
Communication between different parts of the cortex.
layer 2= Granular layer receiving inputs
layer 3= Pyramidal layer creating outputs
What is the main function of layer 4?
It receives thalamic input.
The sensory cortices have a thiqq layer 4 as they receive a lot if input via the thalamus.
Granular layer
What is the main function of layer 5?
Layer 5 projects to non-cortical targets.
Motor cortex has a thiqq layer 5 as it projects a lot of axons for motor action.
Pyramidal layer
Who used cortical layers to map the brain into functional areas?
Korbinian Brodmann mapped the brain into 52 areas based on their cytoarchitectonics.
Columnar organization of neocortex
Refers to the way patches of cortex is bound together in functional units by vertical layers that span all 6 layers.
It is best studied in primary visual cortex, where it is very clear in e.g. ocular dominance columns (ice cube model)
It is difficult to study in the association cortices, but it is very likely that they also follow a comparable columnar organization.
Association cortices are basically the entire cortex, except for the ____
Primary sensory and motor areas
How are the association cortices different from the primary motor and sensory areas?
- Thick layers 2/3 due to a lot of corticocortical connections.
- Signals to association cortices reflect information already pre-processed in primary cortices
- Connections from brainstem and basal forebrain contributing to learning, motivation, arousal etc.
The parietal Association cortex
Recall the ‘Where’ pathway.
Involved with attention to and awareness of the body and surroundings.
I.e. where is my hand in relation to the coffee cup.
Also associated with attention in general and reward evaluation.
In macaques, more juice = more activation in parietal cortex
The temporal association cortex
Recall ‘What’ pathway.
Recognition, identification and naming of stimulus. Wernicke’s area in the lateral temporal lobe is especially involved with naming things.
Includes fusiform face area involved with recognising faces.
Prosopagnosia
Inability to recognise or distinguish faces.
Primarily occurs from birth, without brain damage, but can also be caused by damaged to the fusiform face area
Wernicke’s aphasia (Fluent aphasia)
A type of aphasia with poor comprehension. Speech is effortless but the meaning is impaired.
Caused by damage to the left lateral temporal lobe.
Remember Byron:
https://www.youtube.com/watch?v=3oef68YabD0&ab_channel=tactustherapy
Describe the delayed response task involving macaques with frontal lesions.
A researcher places food into one of two receptacles while the monkey is looking. A screen is then lowered to cover the monkeys view of the receptacles. When the screen is elevated again, monkeys without frontal lesions easily learn to grab the food from the receptacle, while lesioned monkeys don’t.
