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Task 7: The Adding effect (Hampton et al (VMPFC+ amygdala (respond in…
Task 7: The Adding effect
Murray et al.
amygdala
tags events, objects, options in the environment with affective value (positive and negative)
sends this affective tag to the cortical regions involved in storing and updating the associations between events and outcomes
for stimulus-reward associations- lOFC
action-outcome associations- anterior midcingulate cortex aMCC/dACC
2 main misconceptions
amygdala is only involved in negative emotion - in fact it is involved in both positive and negative emotion
evidence for positive emotion - STUDY by Patron et al.
METHOD: showing pictures with positive and negative valance (assured through pavlovian conditioning) and then changing the associations to the opposite-valence. if amygdala showed stimulus-valence pairings, its activity should be changing over time.
RESULTS: amygdala's activity changed, turned out one population of neurons in BLA responded to positive and one population to negative valence (no obvious segregation between these two)
more evidence- Lesions studies
amygdala lesions - damage in CeA and BLA caused fail in approach behavior in rats
amygdala lesions in monkeys- fail to update current value of food (but expectations of value are stored somewhere else)
BLA- encoding the predictive relationship between stimuli and primar reinforcers + encodes positive valence as often as negative ones
When BLA neurons discharge: facilitates impulse transmission between perirhinal + entorhinal cortex
Amygdala enhaces sensory processing in the rhinal cortex
Rhinal cortex: gateway for sensory information to hippocampus enhaces processing + storing of emotional memories
Amygdala is facilitating hippocampal-dependent information storage
Evidence from human amygdala
right amygdala was selectively sensitive to faces that had been associated with emotional descriptions – either positive or negative
subjects expressed a preference for images paired with a high reward probability, although they remained unaware of the relationship between the images and food probability
to SUMM UP
amygdala mediates an association between sensory inputs and their affective valence
people can remain unaware of these associations yet behave on them
role of the amygdala for positive emotions is at least as important is its role for negative ones
amygdala contributes to stimulus-reward processing - where in fact it is essential for only a fraction of stimulus-reward processing (neural substrates for emotion and reward are partially nonoverlapping)
Dissociation between neural bases of emotion and reward were found
monkeys with selective amygdala lesions:
a) reduced emotional reactions, but no impairment on tests of stimulus-reward learning (object-reversal learning)
b) in test of extinction: were facilitated in reward processing
two tasks that have linked the amygdala with stimulus–reward association in monkeys (win-stay, lose-shift task + object-reversal learning task) do not depend on the amygdala
how could the monkeys perform these tasks without an amygdala?
quickly learn a visually based performance rule
treat the positive reinforcement as they would any other sensory signal
occurrence of food guides the selection of a performance rule - independent of the amygdala
role of food is largely limited to its informational value, not its reinforcing / emotional value
several brain regions (amygdala, OFC, ACC) involved in responding to emotion-provoking cues + regions are ot the same as for stimulus-reward processing
ANATOMY
Central amygdala
mediates a feneral affective reaction
promotes appropriate skeletomotor and autonomic response to a particular oportunity or threat
BLA
mediates a more specific affective reaction (one linked to the sensory properties of the reinforcer)
CIRCUITRY
Amygdala - medial frontal cortex
associating actions (opposed to cues) with current biological value
amygdala - IT/PRh
enhance sensory processing of biologically significant stimuli and events
amygdala -OFC
updating the values of expected outcomes (amygdala)
storing the values of expected reward outcomes (OFC)
enable animals to choose between multiple competing cues, based on the current value of associated outcomes
to maximize positive outcomes + to minimize negative ones
contribute to goal-directed behavior and decision making
BUT: OFC also influences amygdala
Processing affective information
IT/PRh - frontal cortex
implementation of visually guided rules
object-reversal learning + other visually guided rules
processing visual information
De Martino et al.
game theory - assumption of extensionality / invariance (logical consistency across decisions, regardless, of the maner in which avaliable choces are represented
Kahneman and Tversky - FRAMING EFFECT - human choices are susceptible to the manner in which options are presented (prospect theory)
STUDY
AIM: investigate the neurobiological basis of the framing effect
METHODS: fmri + financial decision making task: choose between SURE/GAMBLLE option and GAIN/LOSE frame
RESULTS:
NEUROLOGICAL
amygdala activation was significantly greater when subjects decided to choose the sure option in the Gain frame (Gsure – Ggamble) and the gamble option in the Loss frame (Lgamble -Lsure)
central role in mediating the frame effect
brain areas when their decisions ran counter to their general behavioral tendency (Ggamble + Lsure): enhanced activity in ACC + to a lesser extend dlPFC. Also subjects wo acted more rationally exhibited greater activation in OMPFC associated with frame effect
BEHAVIORAL
risk aversion in gain frame, risk-seeking in lose frame (60/40 ratio)
Hampton et al
VMPFC+ amygdala
respond in anticipation of an impending outcome
firing rates of these neurons track changes in reward contingencies over time computing and rapidly updating reward expectations
neurons respond to stimulus cues predictive of future rewarding or punishing outcomes
guiding behavioral choice under uncertainty
learning associations between stimuli and subsequent reward or punishment
STUDY
AIM: investigate the effects of amygdala lesions on reward representations in vmPFC
METHODS: study changes in brain activity in two patients with focal bilateral amygdala lesions. - prpabilistic reversal learning task - presenting 2 stimuli, every correct stimuli grants higher reward ratio than incorrect stimuli. after 4 correct choices te ratio of rewards changes, o the subjects have to switch their choice. After that they had deterministic task, where stimuli was 100% gain and 2nd was 100% loss
HYPOTHESIS: amygdala contributes to computations of expected reward value in vmPFC, which in turn should affect signals of behavioral choice
RESULTS
Switching Behavior
more likely to switch generally, also more likely to switch after a reward
fMRI results
greater activity during switch compared with stay in anterior frontal insula, posterior lateral orbitofrontal cortex (OFC) + ACC
in stay trials compared to switch: significant effects in medial PFC (mPFC
significantly greater responses in switch trials in control subjects than in amygdala lesions in anterior insula/posterior lateral OFC bilaterally
bilateral damage to the amygdala results in altered responses in anterior insula/ posterior lateral OFC and ACC related to behavioral choice
Expected Reward Signals
control subjects: significant correlations with this signal in orbital and medial PFC - time-locked to the time of choice. Activity in these areas increases in a linear fashion as a function of increasing expected reward value encoding the expected reward of the currently chosen stimulus
amygdala lesions vs. control
significantly weaker correlation with expected reward in mPFC
responses in mPFC in the amygdala lesion subjects did not display a clear linear increasing relationship with expected reward
amygdala lesion subjects process the expected reward value of each choice abnormally
Responses to Rewarding and Punishing Outcomes
control
activity relating to reward in medial PFC and medial OFC
activity to punishing outcomes: anterior ventrolateral PFC extending into lateral OFC
Amygdala Lesion vs. controls
no significant differences in BOLD responses to rewarding or punishing feedback
processing of rewarding and punishing feedback in OFC and mPFC remains intact after amygdala lesions
SUMMARY
orbital, medial, and lateral PFC: computation of expected reward of behavioral choice based on such reward
depend on input from the amygdala
vmPFC: reward outcome representations not as dependant on amygdala input
posterolateral OFC, anterior insula, ACC: behavioural choice
signals reduced in amygdala lesions
production of signals related to behavioral choice relies directly on input from the amygdala
amygdala lesions appear to selectively impair the generation of expected reward signals in PFC + signals for behavioral choice that would normally be based on those expected reward signals but leave the generation of reward outcome signals essentially unaffected