DIFFERENT TYPES OF FEAR-CONDITIONED BEHAVIOR MEDIATED BY SEPARATE NUCLEI WITHIN AMYGDALA

The amygdala has long been thought to be involved in emotional behavio ur(1,2), and its role in anxiety and conditioned fear has been highlig hted(3,4). Individual amygdaloid nuclei have been shown to project to various cortical and subcortical regions implicated in affective proce ssing(5-7). Here we show that some of these nuclei have separate roles in distinct mechanisms underlying conditioned fear responses. Rats wi th lesions of the central nucleus exhibited reduction in the suppressi on of behaviour elicited by a conditioned fear stimulus, but were simu ltaneously able to direct their actions to avoid further presentations of this aversive stimulus. In contrast, animals with lesions of the b asolateral amygdala were unable to avoid the conditioned aversive stim ulus by their choice behaviour, but exhibited normal conditioned suppr ession to this stimulus. This double dissociation demonstrates that di stinct neural systems involving separate amygdaloid nuclei mediate dif ferent types of conditioned fear behaviour. We suggest that theories o f amygdala function should take into account the roles of discrete amy gdala subsystems in controlling different components of integrated emo tional responses.