Delta activity from amygdala in squirrel monkeys (Saimiri sciureus): Influence of social and environmental context.

Abstract

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.

Amygdalar Lateralization in Fear Conditioning: Evidence for Greater Involvement of the Right Amygdala.

“…As mentioned previously, there appears to be right hemispheric and amygdalar dominance in processing emotional stimuli and fear learning in humans (e.g., Davidson & Tomarken, 1989; Gainotti, 1983; Gainotti & Caltagirone, 1989; Sackeim et al, 1982). Similarly, animal studies also suggest a greater right amygdalar involvement during inhibitory avoidance and contextual fear conditioning (e.g., Coleman-Mesches & McGaugh, 1995a, 1995b; Lloyd & Kling, 1991; Scicli et al, 2000). Anatomical and neurochemical differences between left and right amygdalae might contribute to lateralization effects in contextual fear.…”

“…Paralleling the human studies, there is suggestive evidence for laterality in processing amygdala-dependent fear from animal studies. For example, significantly greater levels of electrical activity (i.e., delta band) have been reported in the right amygdala of squirrel monkeys in an environment where shock was previously administered (Lloyd & Kling, 1991). In rats, immediate posttraining reversible inactivation of the right, but not left, amygdala impaired retention of inhibitory avoidance learning (Coleman-Mesches & McGaugh, 1995a, 1995b), suggesting that the right amygdala is involved to a greater degree than the left amygdala in the consolidation of memory storage for aversive experiences (Coleman-Mesches, Salinas, & McGaugh, 1996).…”

Comparison of emotional responses in monkeys with rhinal cortex or amygdala lesions.

“…Thus, monkeys with selective amygdala damage appear to often ignore the potential threat inherent in unfamiliar, inanimate and social stimuli, following instead their spontaneous exploratory and contact-seeking tendencies. Accordingly, electrical activity in the monkey's normal amygdala reflects the degree of ambiguity of the socioemotional context, the greatest activity being recorded in situations of high uncertainty, such as a conspecific behaving in an unpredictable manner or a setting associated with unpredictable shocks (Kling, Lloyd, & Perryman, 1987; Lloyd & Kling, 1991). Data in monkeys, therefore, fit well with a current model positing the amygdala as part of a “continuous vigilance system, one that is preferentially involved in ambiguous learning situations of biological relevance” (Whalen, 1998, p. 177).…”