Limbic System

Question 1

What are the three primary parts of the limbic cortex?

Answer 1

1. Orbitofrontal - including subcallosal area
2. Cingulate gyrus - surrounding corpus callosum
3. Medial temporal cortex - includes parahippocampal gyrus

Question 2

What is the general function of the limbic cortex?

Answer 2

Exchanges information with vast areas of the neocortex to help integrate all sensory and motor information into a neural representation of “self”

Question 3

Where is the hippocampus located?

Answer 3

Deep to parahippocampal gyrus, adjacent to inferior horn of lateral ventricle, posterior to amygdala

Question 4

How many cellular layers does the cortex have and why?

Answer 4

3 cellular layers, as it is one of the oldest parts of the brain

Question 5

What are the three nuclei of the hippocampus?

Answer 5

1. Dentate gyrus
2. Ammon’s Horn (CA1, CA3)
3. Subiculum

Question 6

What is the general function of the orbitofrontal cortex?

Answer 6

Seat of wisdom, controls your intrinsic motivations

Question 7

What is the general function of the cingulate gyrus?

Answer 7

Control in emotions and sadness -> lesion = no sadness with pain

Question 8

What is the parahippocampal gyrus also called? What is its function?

Answer 8

Entorhinal cortex. Its function is the “gateway to the hippocampus”, receives information from limbic association cortex and projects to the hippocampus

Question 9

What nuclei project directly to the hippocampus for the purpose of fear and pleasure memory?

Answer 9

Amygdala - fear

Septal nuclei - pleasure

Contributes to motivational states

Question 10

What is the purpose of the reticuular formation with respect to the hippocampus?

Answer 10

Project serotonin, dopamine, and norepinephrine to hippocampus for regulation of mood (emotional tone)

Question 11

What is the first nucleus to process information in the hippocampus and what does it do?

Answer 11

Dentate gyrus, receives fibers from entorhinal cortex and projects to Ammon’s Horn and subiculum

Question 12

How do Ammon’s Horn and Subiculum project out, and what neurotransmitter type do they use?

Answer 12

They project out through the C-shaped fornix, with the first part being called the fimbriae.

Entire circuit is excitatory, reinforces memory formation

Question 13

Why is the hippocampus prone to ischemia or seizure?

Answer 13

Entire circuit is excitatory with high energy demands in a small space

Question 14

Where do Ammon’s horn neurons primarily project to?

Answer 14

1. Septal area - for pleasure center, limbic system

2. Back to orbitofrontal cortex - limbic system

Question 15

Where do subiculum neurons primary project to?

Answer 15

Mamillary bodies

Question 16

What is the Papez circuit and what is its function?

Answer 16

Hippocampal efferent (subiculum) -> mamillary bodies -> mtt -> anterior nucleus of thalamus -> cingulate cortex -> entorhinal cortex.

Plays a role in emotions / declarative memory

Question 17

What are two hippocampal efferents which do not travel in the fornix?

Answer 17

Amygdala, entorhinal cortex (since these are directly adjacent)

Question 18

What happened to patient HM?

Answer 18

Anterograde amnesia due to bilateral medial temporal lobectomy for treatment of seizures, destroying his hippocampus

Question 19

What is the other name for Korsakoff’s psychosis and what is its etiology?

Answer 19

Amnestic confabulatory syndrome

B1 deficiency leading to degradation of medial diencephalon, including medial thalamus + mamillary bodies.

Patients are intelligent but have anterograde amnesia, and make up answers to compensate for their memory loss.

Question 20

Where is the amygdala and what surrounds it? What is it derived from?

Answer 20

Almond-shaped nucleus derived from telencephalon. It is anterior to the hippocampus in medial temporal lobe, and surrounded by the piriform cortex. Can be seen under the uncus and is the physical cause of the bulge.

Question 21

What are the four main afferents to the amygdala?

Answer 21

1. Olfactory - for feeding and reproduction
2. Autonomic - from caudal solitary nucleus
3. Visual - integrated from limbic cortex - important in higher animals
4. Mood - from reticular formation

Question 22

What nucleus processes olfactory information in the amygdala?

Answer 22

Corticomedial

Question 23

What nucleus processes visceral and autonomic information in the amygdala?

Answer 23

Central

Question 24

What nucleus processes cognitive information in the amygdala, and is the most important in humans?

Answer 24

Basolateral nucleus -> mostly visual information

Good because dorsolateral prefrontal cortex is also important in cognitive functions “seat of reasoning”

Question 25

What are the amygdala’s efferents and their function?

Answer 25

1. Hypothalamus - feeding, thirst, reproductive, endocrine
2. Brainstem - for PANS and SANS
3. Hippocampus - allow emotions to influence memory
4. DM thalamus + limbic association cortex - integrate cognitive + sensory info about environment

Question 26

What does the amygdala have reciprocal connection with?

Answer 26

DM thalamus and limbic association cortex - for integration of senses + emotions + personality

Question 27

What is the general function of the amygdala?

Answer 27

Aversion center which analyzes the environment for cues which signify danger.

Has a strong function in inducing learning and memory especially when a situation evokes a strong emotional response -> survival

Question 28

What happens when you stimulate the amygdala?

Answer 28

Increased attention, related to induction of fear + defense mechanisms, + SANS response.

Question 29

What is the name of the disease where the amygdala degenerates bilaterally and you lose ability to see fear on peoples’ faces

Answer 29

Urbach-Wiethe disease

Question 30

What does neurotransmitter imbalance of the amygdala underlie?

Answer 30

Anxiety and panic disorders

Question 31

What is Kluver-Bucy syndrome? What are its characteristic features?

Answer 31

symptoms which accompany bilateral damage of amygdala, seen mostly in monkeys.

Marked by hyperorality, placidity (failure to show fear or anger), hypersexuality, and hyperphagia

Question 32

What is the substantia innominata? Where is it located?

Answer 32

Unnamed substance - basal forebrain, located between orbitofrontal cortex and hypothalamus

Question 33

What is the basal forebrain region called in gross view and why?

Answer 33

Anterior perforated substance, due to the blood vessels which enter the ventral telencephalon just rostral to the optic chiasm

Question 34

What three main nuclei make up the basal forebrain? Where are they?

Answer 34

1. Nucleus accumbens - ventromedial extension of caudate
2. Septal nuclei - hangs ventral from septum pellucidum
3. Nucleus basalis of Meynert - ventral to anterior commissure

Question 35

What five things project to the basal forebrain?

Answer 35

Hippocampus, amygdala, limbic cortex, reticular formation, olfactory (medial stria) to septal nuclei

Question 36

What is the only afferent connection to the hypothalamus through the fornix?

Answer 36

Septal nucleus projects to it through the fornix

Question 37

What is the function of nucleus basalis and through what does it project?

Answer 37

Releases acetylcholine to the neocortex via the external capsule (lateral to basal ganglia)

This functions to strengthen memory formation

Question 38

Where does nucleus accumbens project? What is its function?

Answer 38

Hypothalamus and ventral regions of globus pallidus

Functions in regulation of motor patterns associated with addictive behaviors, i.e. smoking, gambling, video games, drugs

Question 39

What is the function of the basal forebrain as a whole?

Answer 39

Gratification center, rats will stimulate themselves for a pleasurable feeling

Question 40

In what way are the septal nuclei similar to nucleus basalis?

Answer 40

Sends cholinergic axons to strengthen memory in relationship to pleasurable experiences, except it projects to hippocampus instead of neocortex (nucleus basalis).