Call responses in the amygdala of the mustached bat, pteronotus parnellii: Stimulus-specific excitation, suppression, and spike timing

In interactions with their conspecifics, social animals are presented with social signals representing different opportunities and dangers. This work reflects an attempt to elucidate how the amygdala, a brain structure intimately involved in social behavior and behavioral flexibility in challenging situations, responds selectively to communication sounds that differ in their acoustic structure and behavioral significance. Our animal model of audiovocal communication is the mustached bat, pteronotus parnellii, a social and vocal bat species whose communication sound repertoire has been characterized acoustically. Some of these sounds have a consistent relationship to aggressive and affiliative behaviors. I hypothesized that amygdala neurons would respond robustly and selectively to calls. I recorded action potentials from 104 single units in the basolateral amygdala (BLA) of 7 awake, restrained mustached bats in response to 14 simple-syllabic calls and their pitch-shifted variants. Amygdala neurons were excited by calls expressing aggression or fear, while spiking was relatively suppressed by an affiliative call. This supports the widely held view that the amygdala is one of the most important structures mediating appropriate fear expression, and further suggests that spike suppression in BLA neurons evoked by safety signals is a mechanism for inhibiting inappropriate fear. I also examined whether a neuron's call preference is related to the anatomical location of the recording site within the BLA. Analysis of instances where dorsal and ventral neurons were recorded from the same penetration provided evidence that ventrally located neurons were subject to more frequent call-evoked spike suppression than their dorsal counterparts.;To determine whether preference for motivationally significant call types is a specific property of BLA neurons, we compared their call responses to those of neurons in the primary auditory cortex. Neurons of the primary auditory cortex showed a different pattern of responding across call types, which did not indicate selectivity for calls based on motivational significance. Instead, cortical neurons showed more precise time-locking to stimuli, consistent with responses triggered by discrete acoustic features, in contrast to relatively slower modulations of firing rate induced in BLA neurons.