Limbic System

Question 1

What are the parts of the Limbic System?

Answer 1

• Hippocampal formation (hippocampus, dentate gyrus, the subiculum, and entorhinal cortex) - memory
• Amygdala - emotions
• Septal nuclei

Question 2

What are the Functions of the Limbic System?

Answer 2

• Visceral—smell
• Sex drive
• Memory/Learning
• Behavior and emotions

Question 3

What is Papez Circuit?

Answer 3

Axons of hippocampal pyramidal cells converge to form the fimbria and, finally, the fornix. The fornix projects mainly to the mammillary bodies in the hypothalamus. The mammillary bodies project to the anterior nucleus
of the thalamus (mammillothalamic tract). The anterior nuclei project to the cingulate gyrus, and the cingulate gyrus projects to the entorhinal cortex (via the cingulum). The entorhinal cortex projects to the hippocampus (via the perforant pathway).

Question 4

What does cause Anterograde Amnesia?

Answer 4

Bilateral damage to the medial temporal lobes including the hippocampus results in a profound loss of the ability to acquire new information, known as anterograde amnesia.

Question 5

What are the features of Korsakoff Syndrome?

Answer 5

Anterograde amnesia is also observed in patients with Korsakoff syndrome. Korsakoff syndrome is seen mainly in alcoholics who have a thiamine deficiency and often follows an acute presentation of Wernicke encephalopathy. Wernicke encephalopathy presents
with ocular palsies, confusion, and gait ataxia and is also related to a thiamine deficiency.

In Wernicke-Korsakoff syndrome, lesions are always found in the mammillary bodies and the dorsomedial nuclei of the thalamus.

In addition to exhibiting an anterograde amnesia, Korsakoff patients also present with retrograde amnesia. These patients confabulate, making up stories to replace past memories they can no longer retrieve.

Question 6

What are the features of Klüver-Bucy Syndrome?

Answer 6

Klüver-Bucy syndrome results from bilateral lesions of the amygdala and hippocampus.
These lesions result in:
• Placidity—there is marked decrease in aggressive behavior; the subjects become passive, exhibiting little emotional reaction to external stimuli.
• Psychic blindness—objects in the visual field are treated inappropriately. For example, monkeys may approach a snake or a human with inappropriate docility.
• Hypermetamorphosis—visual stimuli (even old ones) are repeatedly approached as though they were completely new.
• Increased oral exploratory behavior—monkeys put everything in their mouths, eating only appropriate objects.
• Hypersexuality and loss of sexual preference
• Anterograde amnesia

Question 7

What are the features of Alzheimer disease?

Answer 7

• Alzheimer disease accounts for 60% of all cases of dementia. The incidence increases with age.
• Clinical: insidious onset, progressive memory impairment, mood alterations, disorientation, aphasia, apraxia, and progression to a bedridden state with eventual death
• Biochemically: low AcCh in the hippocampus
• Microscopically: neurofibrillary tangles, senile plaques, amyloid angiopathy
• Five to 10% of Alzheimer cases are hereditary, early onset, and transmitted as an autosomal dominant trait.
Lesions involve the neocortex, hippocampus, and subcortical nuclei, including forebrain cholinergic nuclei (i.e., basal nucleus of Meynert). These areas show
atrophy, as well as characteristic microscopic changes. The earliest and most severely affected areas are the hippocampus and temporal lobe, which are involved in learning and memory.