Chapter 26 - Association Cortex and Cognition Flashcards
Studies on the association cortex indicate that it is possible to divide the association cortex in three parts that are specialized for certain cognitive tasks. Which cortexes and which tasks?
- Parietal association cortex
- Attending to stimuli in the external and internal environment. - Temportal association cortex
- Identifying the nature of such stimuli - Frontal association cortex
- Selecting and planning appropriate behavioral responses.
Most of the cortex that covers the cerebral hemispheres is of a certain classification or type. This type is called…
Neocortex.
What is neocortex?
Neocortex is defined as cortex that has six cellular layers, also called laminae.
Despite an overall uniformity of the laminae in the neocortex, regional differences based on these laminar features have long been apparent. These regional differences have allowed investigators to identify numerous subdivisions of the cerebral cortex. These histologically defined subdivisions are referred to as…
cytoarchitectonic areas.
What are cytoarchitectonic areas?
Histologically defined subdivisions of the cerebral cortex defined by their deviance in laminar uniformity.
There are four common features of different cytoarchitectonic areas. What is feature #1?
- Each cortical layer has a primary source of inputs and a primary output target.
There are four common features of different cytoarchitectonic areas. What is feature #2?
- Each area has connections in the vertical axis and connections in the horizontal axis.
There are four common features of different cytoarchitectonic areas. What is feature #3?
- Cells with similar functions tend to be arrayed in radially aligned groups that span all the cortical layers and recieve inputs that are often segregated into radial bands or columns.
There are four common features of different cytoarchitectonic areas. What is feature #4?
- Interneurons within specific cortical layers give rise to extensive local axons that extend horizontally in the cortex, often linking functionally similar groups of cells.
What forms the majority of the input to the association cortices?
Other cortical areas. These projections are called cortiococortical connections.
Corticocortical connections also arise from both corresponding and noncorresponding cortical areas in the opposite hemisphere via …
the corpus callosum and the anterior comissure.
Corticocortical connections also arise from both corresponding and noncorresponding cortical areas in the opposite hemisphere via the corpus callosum and the anterior comissure, which together are referred to as …
Interhemispheric connections.
Most of our evidence about the interconnectivity of the association cortex comes from ..
Most of the evidence comes from anatomical tracing studies in non-human primates, supplemented by the limited pathway tracing that can be done in human brain tissue postmortem.
Most of our inferences about the interconnectivity of the association cortex comes from ..
Observations of patients with cortical lesions.
The first account of the link between parietal lobe lesions and deficits in attention or perceptual awareness came from whom?
The British neurologist W.R. Brain reported three patients with unilateral parietal lobe lesions in whom the primary problem was varying degrees of difficulty paying attention to objects and events contralateral to the lesion. The patients were able to see things in the contralateral field of view, but nevertheless seemed to ignore their presence.
The British neurologist W.R. Brain reported three patients with unilateral parietal lobe lesions in whom the primary problem was varying degrees of difficulty paying attention to objects and events contralateral to the lesion. Based on a large number of patients studied since Brain’s pioneering work, these deficits are now referred to as …
contralateral neglect syndrome.
How has case-studies on contralateral neglect syndrome helped our knowledge of the association cortex?
Since Brain’s original description of contralateral neglect and its relationship to lesions of the parietal lobe, it has been generally accepted that the parietal cortex, particularly the inferior parietal lobe, is the primary cortical regions governing attention.
Contralateral neglect syndrome is typically associated with damage to the left/right parietal cortex.
Right
Contralateral neglect syndrome is typically associated with damage to the right parietal cortex. Why?
This is because the right parietal cortex mediates attention primarily to both the right and left halves of the body and extrapersonal space, whereas the left hemisphere mediates attention primarily to the right. This hemispheric bias is thought to arise from specialization of the left hemisphere for language, thereby driving attentive functions into the right hemisphere.
A right hemisphere lesion causes contralateral neglect syndrome. How severe would this neglect be, and in what direction?
A right hemispheric lesion would cause severe left neglect.
A left hemisphere lesion causes contralateral neglect syndrome. How severe would this neglect be, and in what direction?
A left hemispheric lesion would cause minimal right neglect, because the right hemisphere also mediates attention to the right.
A parietal billateral lesion causes contralateral neglect syndrome. How severe would this neglect be, and in what direction?
A bilateral lesion would cause severe right neglect, and a moderate to severe neglect to the left.
Studies of rhesus monkey’s using single-neuron recordings in the parietal cortex reveal what?
Certain neurons increase their firing rate when the monkey’s attention is directed towards a certain object. When the target was ignored, the firing was small. When the target was attended to, the firing rate spiked. When given fruit juice rewards for attending to certain targets, the activity of some neurons in the parietal cortex varied systematically as as function of the amount of juice associated with each target (and therefore probably the amount of attention paid by the monkey to the target).
What are agnosias?
Agnosias (Greek, “uknown”) are disorders where patients have difficulty recognizing, identifying and naming different categories of objects. They are typically caused by lesions in the association cortex in the temporal lobe.
