24.3 Components and Connections of the Limbic System

Question 1

Which systems provide input to the limbic system?

Answer 1

• Sensory
• Reward
• Decision making

Question 2

What does the parahippocampal gyrus have?

Answer 2

Reciprocal connections with most associated cortex

Question 3

What is the Papez circuit?

Answer 3

The circuit found within the limbic system.

Question 4

Draw and describe the Papez circuit.

[IMPORTANT]

Answer 4

The circuit goes in this order:

• Cingulate gyrus (1)
• Parahippocampal gyrus (via the cingulum)
• Denate gyrus + Hippocampus (2) (via the perforant path)
• Fornix/fibria
• Mammillary bodies (3)
• Mammillothalamic tract
• Anterior nucleus of dorsal thalamus

And then back to the cingulate gyrus.

Question 5

What is the amygdala and where is it found?

Answer 5

• It is a collection of nuclei in the medial part of the anterior pole of the temporal lobe.
• It is part of the limbic system and it one of the most important parts of the brain for emotion.

Question 6

Describe the structure and function of the different parts of the amygdala.

Answer 6

There are 3 main groups of nuclei:

• Basolateral (green) -> Receives input from the auditory, somatosensory and nociceptive systems. Responsible for emotional response and emotional (reward) memory.
• Centromedial -> Outputs to produce visceral responses (e.g. heart rate increases)
• Cortical -> Part of the olfactory cortex

Question 7

Summarise in detail the functions of the amygdala.

Answer 7

• Processing social indicators of emotion -> Especially facial expressions and vocal expressions of fear
• Emotional conditioning -> Learning to associate certain stimuli with fear
• Consolidation of emotional memories -> Memories with stronger emotions (e.g. someone crying) are remembered more strongly
• Inducing the actual feeling of fear?
• Olfactory processing

Question 8

What is the basic circuit of Papez, starting from the hippocampus?

Answer 8

Hippocampus –> mammillary bodies –> anterior thalamic nucleus –> cingulate gyrus –> entorhinal cortex –> hippocampus

(He-Man Ate Cat)

Question 9

Which structure links the hippocampus to the mammillary bodies?

Answer 9

Fornix

Question 10

Which structure links the mammillary body to the anterior thalamic nucleus?

Answer 10

Mammillothalamic tract

Question 11

What is an additional structure that is between the cingulum and entorhinal cortex in the Papez circuit?

Answer 11

Parahippocampal gyrus

Question 12

Where do the anterior thalamic nuclei project to?

Answer 12

Neocortex

Question 13

What does the parahippocampal gyrus have reciprocal connections with?

Answer 13

Association cortices

Question 14

What are the three main groups of nuclei that make up the amygdala?

Answer 14

• Centromedial
• Cortical
• Basolateral

Question 15

Where is the amygdala?

Answer 15

Medial part of anterior pole of temporal lobe
Adjacent to olfactory cortex

Question 16

What is the function and output of the centromedial nucleus of the amygdala?

Answer 16

• Visceral responses: ANS, endocrine system, simple motor responses
• Output to VMH, neurosecretory hypothalamus

Question 17

What is the function and output of the cortical nucleus of the amygdala?

Answer 17

• Receives olfactory info
• Pheromones –> elicit social and sexual behaviour

Question 18

What is the function and output of the basolateral nucleus of the amygdala?

Answer 18

• Emotional response; input from higher order sensory regions
• Outputs to centromedial nucleus and basal ganglia for planning/action, or thalamus for relay

Question 19

What are the functions of the inputs tobasolateral and central nuclei of the amygdala?

• All sensory association cortices
• Direct sensory input from thalamus
• Cortical amygdala
• Entorhinal cortex/hippocampus
• Cingulate gyrus, prefrontal, septal areas
• Brainstem

Answer 19

• All sensory association cortices: auditory, somatosensory, nociceptive systems
• Direct sensory input from thalamus
• Cortical amygdala: olfactory
• Entorhinal cortex/hippocampus: memory
• Cingulate gyrus, prefrontal, septal areas: emotions, reward processing, top-down control, reinforcement
• Brainstem: visceral sensory

Question 20

What are the efferent pathways from the amygdala?

Answer 20

• Amygdalofugal tract
• Stria terminalis

Question 21

What are the similarities and differences between the amygdalofugal tract and stria terminalis?

Answer 21

• Both project to septa region, hypothalamus, thalamus
• Sria terminalis has a much longer pathway
• Amygdalofugal pathway reaches the PAG and prefrontal cortex which the stria terminalis does not

Question 22

What is this region of the brain?

Answer 22

Orbitofrontal cortex

Question 23

What is the name of the notable neurons in the orbitofrontal cortex?

Answer 23

Error neurons

Question 24

When do error neurons fire?

Answer 24

When there are differences between predicted and real outcomes (dopaminergic)

Question 25

What is this?

Answer 25

Hippocampus

Question 26

The orbitofrontal cortex is part of the...

Answer 26

Prefrontal cortex

Question 27

What is the function of the orbitofrontal cortex?

Answer 27

Involved in assignment of values to certain actions and improves decision making as a subsequent trials are carried out by an individual.

Question 28

What does the preservation of function when the orbitofrontal cortex is lesioned tell us?

Answer 28

as these roles are somewhat preserved with lesions to the area, there is likely a diffuse range of systems within the PFC that also help with the assignment of value, and previously learned values are likely retained