Delta activity from amygdala in squirrel monkeys (Saimiri sciureus): influence of social and environmental context.
A previous study reported that power in the delta band of the amygdala is selectively elevated when primates are exposed to affectively ladened stimuli (Kling, Steklis, & Deutsch, 1979). Radiotelemetric recordings suggested that this elevation was greatest when the animal was confronted with conspecific behaviors that could be interpreted as "ambiguous." In the present study, a specific elevation of delta activity was observed when the animal was placed in an environment in which uncued shock had previously been received, in relation to environments in which shock had always been cued. This occurred even though the conditioned stimulus or unconditioned stimulus (or both) was not presented. A specific elevation in delta activity also occurred when a conspecific was present, in relation to when the animal was alone. Finally, recordings in an environment in which shock training had previously occurred showed a striking lateralization of delta activity in the right amygdala but not in the cortex. At other times, no lateralization was observed.