Amygdala Flashcards
Amygdala
- Consists of nuclei (groups of cells)
- Each nucleus has unique inputs and outputs and neurotransmitter systems
- Provides an important route by which external stimuli can have an impact on emotions
Nuclei of Amygdala
Lateral nucleus (basolateral group of nuclei) ~ input region/ gatekeeper of amygdala: - Receives inputs from sensory systems (visual, auditory, somatosensory (including pain), olfactory, and taste systems)
Central nucleus ~ output region for expression of innate emotional and associated physiological
responses
- Connections to brainstem areas that control specific behaviors and physiological responses
- E.g., emotional reactions like “freezing” close a predator
Basal nucleus ~ output to the striatal areas involved in the control of instrumental behaviors
- Actions performed to reach a goal, such as running to safety in view of predator
affective processing
Recognition of unpleasant emotions, such as fear and anxiety
Role of amygdala
• Important for affective processing
• Associate external stimuli and events with aversive sensory inputs (unpleasant emotions)
- Helps establish emotional significance of external stimuli and events
- E.g., a dark street is associated with physical danger
Bilateral damage to amygdala
• Change in emotional behaviour/ hypoemotionality (depends on the extent of damage)
- Decrease in aggression, increase in indifference
- Not necessarily dramatic
• Lack of fear to the stimuli and situations that commonly evoke fear
- Increased exploration of novel environments and objects
• Klüver-Bucy syndrome (i.e., compulsive eating, hypersexuality, docility, hyperorality, etc. ->
reported in animal research)
• But no effect on most memory tests (with selective amygdala damage)
Damage to amygdala
impact on social learning rather than a global loss in affective behavior
Two aspects of reward
- Feedback: indicates correct responses on a task
- Intrinsic value: preference, like and dislike
- -> amygdala plays role in intrinsic value
stimulus-value associations
Linking objects with their current stimulus value
- E.g., associations between a visual appearance of a stimulus (a new food item) with an incentive value
(how it tastes)
Damage to amygdala in monkeys
• Disturbed association between new items and their intrinsic value
- Putting non-food items in their mouths
- Abnormal willingness to eat meat or other uncommon foods (olives)
• Greater impact on learning new food preferences than on already-established preferences
• Can distinguish edible from non-edible items
Pavlovian fear conditioning
A neutral conditioned stimulus (CS) is paired with an unpleasant unconditioned stimulus
Reinforcer-devaluation task
Training:
• Learn to associate the pyramid with cherries and the
cube with peanuts
Bilateral damage to the amygdala
Tests:
• Fed to satiety with cherries, peanuts or given an empty
bowl
• Select one of two objects (pyramid or cube) associated
with food rewards
• Animals with amygdala lesions select an object
associated with a more preferred food, whether they are
satiated or not, because the object value was not updated
Bilateral amygdala damage & fear
impairs the recognition and recall of facial expressions of fear
–> compromised social behaviour
Amygdala is involved in
- Establishing affective associations
- Registering changes from the neutral status of a stimulus to the affective status
- Establishing unconscious biases and preferences about stimuli (objects, events, people)
- Establishing feelings about abstract ideas, concepts, beliefs, hopes and dreams
- Rational vs. emotional decision making (affective signals influence decision-making)
- Mediating the effect of stress on memory formation and consolidation
- Promotes long-term storage of memories about emotional events
Orbitofrontal cortex
• High-level control of affective state
• Cognitive control of amygdala
- “Conquer” fear, appear/act brave despite high heart rate and change in blood pressure
- Phineas Gage had damage to the orbitofrontal cortex -> lack of impulse control
Orbitofrontal cortex Contribution to stimulus-reward associations
Amygdala is important for making and updating stimulus-reward associations, while the orbitofrontal cortex is required for storage of such associations
Activity of orbitofrontal cortical neurons discriminates between different rewards
- Firing rate reflects the value of expected reward irrespective of the spatial, visual, motor aspects
- Orbitrofrontal cortical neurons represent value in a common mode independent of the type or amount of reward
Cingulate Motor Area Function
• Higher-order motor areas
• Processing of information necessary for voluntary action selection
- Based on subject’s internal and external requirements
• CMAr is particularly active when a subject is required to select movements voluntarily in different motor tasks
Cingulate Motor Area and Reward
CMAr is critically involved in voluntary motor selection based on the amount of reward:
- Assessment of the reward for the current movement
- Selection of the next movement if the reward is not acceptable
Proposed function of the cingulate cortex (including the cingulate motor areas)
• Monitoring of errors and other outcomes
- Detect when actions lead to errors and less rewarding outcomes
- FMRI activity in the cingulate cortex increases when subjects make errors
- Trial-and-error learning
• Encoding a reward prediction based on reward magnitude and reward probability
• Encoding the expected value of actions rather than the expected value of stimuli
- Action-reward relationships are encoded more than stimulus-reward relationships
• Processing the information about the consequences of actions rather than the associations of stimuli
- Removal of the cingulate cortex does not impair learning of visual discriminations
