Limbic system

Question 1

What is emotion?

Answer 1

Combination of psychological and physiological responses to a stimulus.
A state of affect.

Question 2

What is normal emotion?

Answer 2

Normally there is a range of emotions.
But there is a lot of variety in individuals and across a population.
Hard to define what is an abnormal state of emotion.

Question 3

What is the purpose of emotion?

Answer 3

Interpersonal communication.
We can tell how a person is feeling based on the small change in facial expressions, which are capable because of the large amount of motor control in the face.
Emotion can aid memory - memories can be more strongly encoded if they are associated with a strong emotional response.

Question 4

What questions have been asked about emotion?

Answer 4

Is there one discrete region for emotion? Do we have a primary emotion cortex? No.
Is there one discrete region for each type of emotion. No
There is a functional network of neurones involving many structures in a circuit.
Which structures of the brain are involved? The limbic structures - border.

Question 5

What happens physiologically in emotion?

Answer 5

In a particular emotional state, we express a specific physiological change e.g. pupils dilate, crying, heart rate change.
This is due to changes in the autonomic system.

Question 6

How is the limbic system linked to emotion (Papez circuit)?

Answer 6

The hypothalamus controls the changes in the autonomic nervous system.
The cingulate gyrus communicates with the neocortex.
The neocortex is responsible for the conscious awareness of emotion.
Hippocampus provides context for the emotion.

Question 7

What is the evidence for Papez circuit?

Answer 7

Lesions/damage due to a tumour, infection or traumatic injury cause a change in emotional state.
e.g. damage to the anterior thalamus causes spontaneous laughing and crying.

Question 8

What is the role of the hippocampus in emotion?

Answer 8

The hippocampus is involved in memory formation, if it is a traumatic experience it is more likely to be remembered.
In chronic depression the hippocampus volume is decreased.

Question 9

What is the amygdala?

Answer 9

In the temporal lobe. One on each side of the brain.
It is part of the limbic system as it is not visible from outside the brain.
It is important for extreme negative emotions e.g. fear. In a temporal lobectomy the sense of fear is lost.

Question 10

What is the structure of the amygdala?

Answer 10

The amygdala is small, but has subregions of the corticomedial nuclei, central nucleus and basolateral nuclei.
See picture.

Question 11

What is the role of the amygdala in epilepsy?

Answer 11

In temporal lobe epilepsy the temporal lobe is the origin of the seizure.
The person has a sense of fear which warns them they are about to have a seizure, which is due to the heightened activity in the temporal lobe, including the amygdala.

Question 12

Why do you need emotional memory?

Answer 12

Intepretation of sensory input.
Feedback to retain important sensory stimuli so you avoid certain situations in future. e.g. a food you don’t like.

Question 13

What is the role of the amygdala in emotion circuitry?

Answer 13

Stimulus into the sensory cortex which then signals to the amygdala.
The amygdala communicates with the hypothalamus to adjust autonomic control.
Communicates to the periaqueductal grey to trigger a behavioural response.
Communicates to the neocortex for emotional experience - recognise the emotion.

Question 14

What is the clinical relevance of dysfunctional amygdala?

Answer 14

In extreme emotional conditions there is evidence of changed function in the amygdala e.g. anxiety, PTSD, depression, autism and aggression.
If the brain is plastic enough to change and generate this emotional state, then it is plastic enough to be reversed back.
Clinical interventions can be based on this thinking to change it back.

Question 15

How can the circuitry be manipulated to treat emotional disorders?

Answer 15

Psychosurgery - frontal lobotomy.
Deep brain stimulation
Drugs

Question 16

What is the effect of a frontal lobotomy?

Answer 16

Reduces anxiety and agitation.
Blunted emotional response.
Decision making was reduced because they couldn’t take into account how the decision would affect their emotional state.

Question 17

What is a frontal lobotomy for depression?

Answer 18

Severing of the axons which supply the frontal cortex.
This could be used in extreme depression where the individual is in constant danger of committing suicide.
But the lobotomy blunts all emotional response, not just the depression.
This is not done in modern times.

Question 19

What is deep brain stimulation?

Answer 19

Drives a change in the electrical activity through electrodes into specific brain structures.
This could be used in major depressive disorder.

Question 20

What is lateralisation?

Answer 20

Certain functions of the brain are more strongly controlled by one hemisphere (left or right) than the other.
The right hemisphere is specialised for recognising and expressing emotions, especially negative.
The left hemisphere is more specialised for positive emotions.