Three forebrain structures directly inform the auditory midbrain of echolocating bats

Abstract

Echolocating bats emit various types of vocalizations for navigation and communication, and need to pay attention to vocal sounds. Projections from forebrain centers to auditory centers are involved in the attention to vocalizations, with the inferior colliculus (IC) being the main target of the projections. Here, using a retrograde tracer, we demonstrate that three forebrain structures, namely, the medial prefrontal cortex (mPFC), amygdala, and auditory cortex (AC), send direct descending projections to the central nucleus of IC. We found that all three structures projected to the bilateral IC. A comparison of the patterns of retrogradely labeled cells across animals suggests that the ipsilateral AC-IC projection is topographically organized, whereas mPFC-IC or amygdala-IC projections did not show clear topographic organization. Together with evidence from previous studies, these results suggest that three descending projections to the IC form loops between the forebrain and IC to make attention to various vocal sounds.

Keywords: Auditory cortex; Basolateral amygdala; Descending projection; Inferior colliculus; Medial prefrontal cortex.