Frontal Lobes and Hippocampus

Question 1

Describe the basic deficits observed with selective injury to the dorsolateral components of the prefrontal corticies

Answer 1

Damage to this region results in the inability to make goals or employ intention. Additionally, patients would not be able to modulate attention. This causes perseveration, meaning they can’t switch attention and focus inappropriately on a single task. This also results in environmental dependency, whereby the lack of internally generated goal direction and patients are forced to rely on environmental cues to accomplish a task

Question 2

Describe the basic deficits observed with selective injury to the ventromedial components of the prefrontal corticies

Answer 2

Damage to these structures cause specific findings on the Iowa Gambling Test: patient continue to draw from the bad deck, even though they know they are losing. Additionally, these patients do not show stresses responses to impending punishment. In other words, patients have impaired ability to estimate the risks and rewards associated with certain behaviors. Patients can have a loss of inhibition of aggression, sexual behaviors, anxiety and appetite and fail to employ these behaviors in appropriate circumstances.

Question 3

Describe the basic deficits observed with selective injury to the anterior cingulate components of the prefrontal corticies

Answer 3

Patients with damage to this structure have a decrease in goal directed behavior, with diminished initiative, perseverance, productivity and effort which results in a dependence on others to structure and support all of their activities. They have both decreased goal-directed cognition (eg intellectual interest) and decreased emotional experience and responsiveness (eg flat affect and lack of emotional response). They can show abulia or akinetic mutism.

Question 4

Understand the result of bilateral hippocampal dysfunction

Answer 4

Loss of bilateral hippocampus function results in a loss of the ability to form declarative memories and episodic memory. Memory storage is intact, so patients may remember memories they formed previous to the lesion in the hippocampi. Additionally, these patients would likely struggle with spatial memory, a type of declarative memory specifically concerned with locations in space

Question 5

Understand how different sensory components of an episode appear to be combined in the hippocampus

Answer 5

Cells of the CA3 field of the hippocampus form autoassociations with themselves and their neighboring cells. This characteristic is the basis for autoassociative memory; a form of neural network that allows us to retrieve entire memories when presented with only a small portion of the memory. CA3 autoassociations effectively function as a single network connected by collaterals to other CA3 cells and allows associations between inputs originating at different parts of the cerebral cortex to be formed. In other words, hippocampal networks integrate parallel streams of information (ex. spatial and non spatial) which then act as a scaffold onto which other aspects of a specific event can be bound.

Question 6

Understand the apparent importance of sleep in hippocampal-dependent memory consolidation

Answer 6

The neocortex and the hippocampus interact during sleep to consolidate memories. Memory is retained in the hippocampus for approximately 1 week during which representations of recent experiences are transferred to the neocortex (in reverse order) during sleep. When the information is recalled, it strengthens cortico-cortical connections, making the memory independent of the hippocampus.

Question 7

What are the three major regions of the hippocampus?

Answer 7

1. Dentate Gyrus = Principal cell type are granule cells
2. Hippocampus/Ammon’s Horn = Principal cell type are pyramidal cells
   Further subdivided: CA3 field (Adjacent to dentate), CA2 field and CA1 field (Merges with the subliculum)
3. Subliculum

Question 8

Major input/output of hippocampus

Answer 8

Entorhinal Cortex input

a. Entorhinal Cortex axons to dentate gyrus
b. Granule cells of the dentate gyrus send axons to CA3 field of hippocampus (these projections are called Mossy fibers)
c. Pyramidal cells of CA3 field send axons to the CA1 field AND back to CA3 cells via Schaffer collaterals to form autoassociations!
d. CA1 field cells project axons to the subliculum
e. subliculum axons are sent back to the entorhinal cortex which sends projections to most cortical association areas