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, 25 (12), 2124-40

The Impact of Early Amygdala Damage on Juvenile Rhesus Macaque Social Behavior

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The Impact of Early Amygdala Damage on Juvenile Rhesus Macaque Social Behavior

Eliza Bliss-Moreau et al. J Cogn Neurosci.

Abstract

The present experiments continue a longitudinal study of rhesus macaque social behavior following bilateral neonatal ibotenic acid lesions of the amygdala or hippocampus, or sham operations. Juvenile animals (approximately 1.5-2.5 years) were tested in four different social contexts--alone, while interacting with one familiar peer, while interacting with one unfamiliar peer, and in their permanent social groups. During infancy, the amygdala-lesioned animals displayed more interest in conspecifics (indexed by increased affiliative signaling) and paradoxically demonstrated more submission or fear (Bauman, Lavenex, Mason, Capitanio, & Amaral, 2004a, this journal). When these animals were assessed as juveniles, differences were less striking. Amygdala-lesioned animals generated fewer aggressive and affiliative signals (e.g., vocalizations, facial displays) and spent less time in social interactions with familiar peers. When animals were observed alone or with an unfamiliar peer, amygdala-lesioned animals, compared with other subjects, spent more time being inactive and physically explored the environment less. Despite the subtle, lesion-based differences in the frequency and duration of specific social behaviors, there were lesion-based differences in the organization of behavior such that lesion groups could be identified based on the patterning of social behaviors in a discriminant function analysis. The findings indicate that, although overall frequencies of many of the observed behaviors do not differ between groups, the general patterning of social behavior may distinguish the amygdala-lesioned animals.

Figures

Figure 1
Figure 1
Experimental Timeline. Note: Hashmarks on time access indicate months. [a] Mean age at the start of observations was 1.44 years (SD = 0.09). Mean age at the end of observations was 2.09 years (SD = 0.08). [b] Mean age at the start of observations was 2.17 (SD = 0.08). Observations were completed 4 weeks later. [c] Mean age at the start of observations was 2.34 years (SD = 0.10). Mean age at the end of observations was 2.46 years (SD = 0.10). [d] Mean age at the start of observations was 2.22 years (SD = 0.09). Mean age at the end of observations was 2.69 years (SD = 0.09).
Figure 2
Figure 2
Classification of lesion groups based on [a] the duration of time spent in social states and [b] the frequency of social states during familiar dyads. Each individual data point represents a single animal. In both cases, Function 1 maximally separated control from lesion groups.

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