The amygdala, reward and emotion
According to current thinking, the amygdala contributes to emotion, reward, motivation, learning, memory and Attention (the
specific contribution of the amygdala to them, remains one of the central challenges in cognitive Neuroscience).
‘reward’ = something that an animal will work to obtain (if positive) or avoid (if negative).
•Reinforcement received after performance of an action also functions to increase the probability that the same action
will be repeated
•rewards might influence behavior through Pavlovian mechanisms that operate independently of actions
Amygdala function in positive affect
Neurophysiological studies in monkeys provide strong evidence for a role for the amygdala in positive affect.
•Paton et al. recorded from single neurons in the amygdala while visual stimuli acquired a positive or negative
valence through Pavlovian conditioning.
•To determine whether neuronal activity reflected reinforcer valence, rather than stimulus features, pictures
that initially signaled the agreeable liquid later signaled the aversive air puff, and vice versa.
■amygdala activity reflected stimulus–valence pairings, so neuronal activity changed over trials to
reflect the new pairings
•neurons encoding positive valence and neurons encoding negative valence most were in
the basolateral portion of the amygdala
the recent results make it clear that the amygdala has signals related to positive, as well as negative, reinforcement
■Studies of reinforcer devaluation also demonstrate the role of the amygdala in positive affect
•amygdala lesions cause dramatic deficits in the ability of monkeys to choose an object based on the current
value of a food reward associated with that object.
■Unlike intact monkeys, which avoid an object associated with a food recently consumed to
satiety, monkeys with amygdala lesions choose an object associated with a more preferred food,
whether devalued by selective satiation or maintaining a high value
the role of the amygdala is limited to updating the monkeys’ estimation of the current biological
value of the food. Once the updating function has been accomplished, the amygdala is no longer
necessary for choosing objects based on current food value.
Studies of Pavlovian approach behavior in rats also inform the role of the amygdala in positive affect.
■Rats are exposed – on separate occasions – to two different stimuli, and food is provided in association with only
one of them. Later, both stimuli appear simultaneously but no food shows up. Although the animals do not need to
do or learn anything, they nevertheless spend more time near the stimulus associated with the food. (This Pavlovian
approach behavior reflects a tendency to associate physically with stimuli of positive affective valence)
•In some experimental settings, rats with lesions of the central nucleus of the amygdala (CeA) fail to show
approach behavior; in others, damage to portions of the BLA, which consists of the lateral, basal and
accessory basal nuclei, lead to this impairment
■Schoenbaum et al. also reported that neuronal activity in the rat BLA reflects stimulus–reinforcer associations,
including positive ones.
Taken together, the data in rats and monkeys provide strong support for the idea that the BLA is involved in encoding
the predictive relationship between stimuli and primary reinforcers such as food and fluids, and that it encodes positive
valences as often as negative ones.
Functional imaging studies in humans have likewise provided evidence supporting the role of the amygdala in positive affect
•Faces presented to subjects, then associated with positive, negative or neutral characteristics
•the right amygdala was selectively sensitive to faces that had been associated with emotional descriptions
– either positive or negative. Sometimes the same subjects could not report the information associated with
the faces
the amygdala generates a nonspecific arousal signal but their results are equally compatible with the idea
that the amygdala encodes stimulus–valence associations that are sometimes inaccessible to conscious
awareness.
•human subjects presented with two-dimensional abstract images, each paired with a high, medium or low probability
of food reward
