The Limbic System

Question 1

What are the core components of the Limbic system?

Answer 1

Amygdala (responsible for emotion), the hippocampus (and cortex, responsible for memory), Limbic Cortex (consists of cingulate gyrus and insula.

Question 2

What are the effectors of the limbic system?

Answer 2

Hypothalamus and brain stem structures

Question 3

What are the different sections of the amygdala and where is the amygdala found?

Answer 3

Basal and lateral nuclei, central nucleus and the corticomedial nucleus. The amygdala is found in the anterior temporal lobe at the rail of the caudate nucleus, rostral to hippocampus.

Question 4

What can cause damage to the amygdala and what can it result in?

Answer 4

Herpes encephalitis, trauma, tumours, hypoxia and Pick’s disease, urbach-wiethe disease. It can cause placidity (which is a lack of fear) as well as hyperorality. Some less common symptoms are hypersexuality, memory loss and dementia

Question 5

What is the function of the amygdala?

Answer 5

It controls emotional reactions (particularly fear/threat) via effectors such as hypothalamus and brain stem. It generates and is activated by fear (emotional response). Fear causes activation of central nucleus and the bed nucleus of the stria terminalis. It stores simple ‘codes’ of values.

From textbook - It is involved in immediate behavioural and physiological responses to threat

Question 6

What are some of the inputs into the amygdala

Answer 6

• Stimulus via visual or auditory pathways. Concepts which are delivered via the cerebral cortex. and Context (snake in the room) which is delivered via the hippocampus.
• Recieves output from the central nucleus
• All inputs go into the lateral nucleus of the amygdala

Question 7

Describe the role the amygdala plays in emotional memory

Answer 7

The amygdala can learn a modified fear response as a certain noise or scene which is associated with fear stimulus can elicit fear due to plasticity.
Textbook - Fear conditioning is a form of emotional learning in which a neutral stimuli becomes associated with an adverse event.

Question 8

How does information from the amygdala reach the hypothalamus?

Answer 8

Via stria terminalis (bundle of white matter)

Question 9

The amygdala output is delivered to what brain stem nuclei?

Answer 9

• Periaqueductal grey matter (PAG),
• Locus coeruleus,
• Parasympathetic nuclei (solitary nucleus, dorsal vagal nuclei)
• Ventral tegmental area.

Question 10

What part of the cingulate gyrus is involved in the limbic cortex and what do they have connections with?

Answer 10

The anterior cingulate gyrus (ACC) which has connections with the amygdala and effectors to brain stem. The anterior portion of the middle cingulate gyrus (MCC) is also involved, and it has connections with the motor cortex

Question 11

What is the role of the anterior cingulate gyrus?

Answer 11

It ‘encodes’ basic emotions such as happiness, sadness, fear and emotional memory.
It can ‘recode’ the amygdala as it has reciprocal connections with the amygdala,
Computes relevance/outcomes,
Provides conflict resolution and is involved in part of the pain network.
- It can bypass the amygdala, it has direct connections to autonomic centres.

Question 12

What are the effectors of the cingulate gyrus?

Answer 12

• Motor reactions which are context specific (drives approach/avoidance behaviour ect),
• Has a specific zone for driving face muscles,
• Has direct output to autonomic system

Question 13

What is the role of the insula (the limbic sensory cortex)?

Answer 13

It is connected to the ACC and the anterior portion is considered to work with the ACC. It recieves input from visceral information including pain. It encodes for emotional awareness and empathy.

Question 14

What is the link between PTSD and the limbic system?

Answer 14

In PTSD, part of the ACC is hypo-responsive, there is reduction in the size of the ACC, it also no longer has top-down control of the amygdala. The amygdala becomes hyper-responsive to trauma related stimuli.

Question 15

What are the major inputs and outputs of the hypothalamus

Answer 15

Recieves direct input from the limbic cortex and amygdala as well as olfactory, sensory systems, viscera, retina and internal signals.
Outputs neuronal and hormonal output to brainstem and spinal cord.

Question 16

What is the hypothalamus involved in?

Answer 16

Autonomic responses such as CV, respiratory, piloerection and sweating.
Endocrine - stress response,
Behavioural responses,
Basic homeostasis.

Question 17

What is the locus coeruleus and what is it involved in?

Answer 17

It is a midbrain nucleus involved in psychological response in panic and stress. Recieves input from the cingulate gyrus, amygdala, PAG and hypothalamus. It has noradrenaline fibres projecting from the nucleus to widespread brain structures so promotes alertness and wakefulness.

Question 18

What is the periaqueductal grey and its functions?

Answer 18

It is a section of grey matter in the midbrain which surrounds the cerebral aqueduct. It mediates limbic autonomic reactions. Has input from cingulate gyrus and amygdala and projects to nucleus of solitary tract, dorsal nucleus of vagus and intermediolateral column.
Projections from here to the LC selects fight or flight.
Can block pain pathways.

Question 19

Describe the periaqueductal grey’s role in defensive fear network and pain network

Answer 19

Defensive; Depends which part of the PAG responds. If the ventrolateral PAG responds then it sends signals via vagal pathways which results in PSNS freezing. If the dorsolateral PAG responds then it sends signals to the LC and BStem causing flight or fight.

Question 20

What is the difference in fear response between a distant and close fear?

Answer 20

At distance the CG processes the response through basolateral amygdala to striatum (causes mild anxiety) whereas at close the central amygdala drives periaqueductal grey and other brainstem centres into panic mode

Question 21

What is the dorsal raphe nucleus and its role

Answer 21

A midbrain nucleus which projects to and recieves from amygdala and ACC. It determines tonic limbic activity and dynamic mood state. It also processes descending pain paths.

Question 22

what is Klüver-Bucy syndrome?

Answer 22

A rare syndrome caused by anterior lobe damage which can damage the amygdala (gave clues as to what the functions of the amygdala is) It results in hyperorality and placidity (lack of fear) can also cause hypersexuality, dementia and seizures.

Question 23

What are some anatomical changes seen in established depression?

Answer 23

Reduced metabolism in ACC, reduced size of ACC and the amygdala is of a reduced size and hyperactive. High density of 5HT transporters, so a 5HTT inhibitor (paroxetine) can treat depression

Question 24

Where is the hippocampus located?

Answer 24

Deep in temporal bones, it is an elongated, rolled structure which is in the floor of the lateral ventricle

Question 25

What are the associated cortex of the hippocaampus?

Answer 25

It is the parahippocampalal gyrus, made up of the

• perirhinal cortex - info about object recognition,
• entorhinal cortex - Main gateway for communication with neocortex.
• parahippocampal cortex - spatial context.

Question 26

What is the subiculum?

Answer 26

Most inferior portion of the hippocampus which is connected to the entorhinal area.

Question 27

What is the function of the hippocampus?

Answer 27

It plays a critical role in memory formation by providing the brain with spaciotemporal framework as well as emotional, sensory and cognitive information. SO it establishes new episodic memories

Question 28

Briefly describe the trisynaptic circuit in the hippocampus

Answer 28

Fibres enter via entorhinal cortex, travels to dentate gyrus then pyramidal cells of CA3 then to pyramidal cells of CA1 then to subiculum (then goes to major outputs)

Question 29

In what diseases can atrophy of the hippocampus be found in?

Answer 29

• Alzheimer’s disease,
• Hypertension,
• Depression,
• Epilepsy,
• Cushing’s disease,
• Stress,
• Genetic disorders,
• Chronic alcohol use

Question 30

What is Wiliams syndrome?

Answer 30

Genetic deletion syndrome in which there is developmental hippocampus effects

Question 31

What is wenicke-korsakoff syndrome?

Answer 31

Thiamine deficent alcohol related hippocampal damage and decrease in hippocampal learning.

Question 32

What is the fornix and its functions?

Answer 32

Major output tract of hippocampus involved in memory. It projects to mammillary bodies. It delivers output information of language, visiospatial (left to right), emotional/motivational learning and scene learning (rostral to caudal segregation).