24.4 Functions of the Limbic System

Question 1

Describe how this neural circuit of the amygdala results in learned fear

Answer 1

• Conditioning –> means that sound tone is associated with pain of electric shock
• Reach basolateral nuclei of amygdala through auditory and somatosensory cortex - relayed to centromedial (central) nucleus
• Enhanced response –> autonomic, behavioural, and emotional responses via the hypothalamus, PAG, and cortex

Question 2

What are the main roles of the limbic system?

Answer 2

• Homeostasis (hypothalamus)
• Emotional control
• Motivation, reinforcing behaviours
• Memory formation
  (- Also connected to olfactory system)

Question 3

What is the role of the hippocampus and dentate gyrus?

Answer 3

Converts short-term memories into long-term memories

Question 4

What are emotions?

Answer 4

Automatic, behavourial and cognitive responses triggered by a stimulus, largely in a subsconscious way

(e.g. feeling of fear - also associated increased heart rate and pupil dilation)

Question 5

What are the three main roles of the amygdala?

Answer 5

1. Processing social signals of emotions (esp fear)
2. Emotional conditioning (fear conditioning)
3. Consolidation of emotional memories

Question 6

What are examples of social signals of emotions that the amygdala processes?

Answer 6

Facial expressions, vocal tone

Question 7

How does the amygdala modulate memories?

Answer 7

• Ensures that a greater emotional response increases strength of the memory of the event
• Through synaptic plasticity - increased interactions between neocortical memory storage sites and temporal lobe areas involved in declarative memory

Question 8

What has been seen with bilateral amygdala damage in patient SM?

Answer 8

• Severely impaired fear conditioning
• Cannot recognise fear in facial expressions
• Impaired social behaviour thought to be related to fear
• No self-reports of fear

Question 9

What is the difference in function between the dorsal and ventral hippocampus?

Answer 9

Dorsal = Spatial memory, time memory (records flow of time)
Ventral = Anxiety and avoidance behaviour

Question 10

What are the functions of the orbitofrontal cortex?

Answer 10

• Context specific responding
• Encoding predicted value of objects that might serve as goals
• Inhibiting unwanted behaviour and emotions

(many things that Phineas Gage could not do)

Question 11

How does the OFC encode predicted values of objects?

Answer 11

• Predicts specific outcomes that should follow sensory events or behavioural choices
• Represents an updated valuation of the predicted outcomes
  –> Good AND bad choices, depending on how valuation has been presented

Question 12

What is the function of the lateral OFC?

Answer 12

Evaluation of opinions independently of each other
Given the sensory and emotional content - from amygdala, hypothalamus (taste, disgust), thalamus etc

Question 13

What is the function of the medial OFC?

Answer 13

Compares and contrasts options presented by lateral OFC to make a choice

Question 14

What is the function of the orbitofrontal cortex?

[IMPORTANT]

Answer 14

• Behavioural inhibition
• Inhibitory self-control
• Emotional regulation

The latest opinion is that the orbitofrontal cortex does not only suppress unwanted behaviours and desires, but also encodes a ‘value’ of certain tasks, taking into account various factors such as difficulty, so that it can provide an updated value for these tasks. Thus, it underlies good and bad choices.

Question 15

What do lesions of the hippocampus cause?

[IMPORTANT]

Answer 15

Associative learning & episodic memory impairment.