Neonatal ablations of the amygdala and inferior temporal cortex alter the vocal response to social separation in rhesus macaques

Rhesus macaques that had received bilateral ablations to either the amygdala or area TE in inferior temporal cortex in the I st week of life were briefly separated from familiar conspecifics at 10-14.5 months of age in order to assess the vocal response to this mild challenge. Sound spectrograms were subjected to quantitative analysis and compared with calls from normal, age matched controls subjected to the same testing conditions. Animals with TE damage called at a higher rate than animals in the other two groups. TE subjects also produced more coos than controls. Males with TE lesions produced noisy calls at a higher rate than males of the other two groups. Females did not differ between groups in this measure. Analysis of the detailed acoustic structure of the 'coo' indicated significant differences in a measure of slope of the fundamental frequency (rate of frequency change over time) between amygdalectomized animals and those of the other 2 groups. The amygdalectomized monkeys produced calls with lower slope values, giving the calls a less inflected quality both in sonagrams and to the listener. These findings suggest an important role for the amygdala and inferior temporal cortex in regulating the vocal response to social separation during development.