Topographical distribution of spectrotemporal receptive field properties in the bat primary auditory cortex

Abstract

Spectrotemporal modulations are a prominent feature of natural sounds including animal vocalizations and human speech. Echolocating bats must process spectrotemporal cues such as echo delays and spectrum properties to navigate their environment; however, the neuronal networks in the primary auditory cortex (A1) that process features of natural sounds remain incompletely understood. Here, we investigated the topographical distribution of tuning properties throughout A1 of Mexican free-tailed bats. While the majority of the bats’ A1 neurons are tuned to downward FM sweeps, the entire cortex is required to capture and categorize patterns of spectral details embedded within each biosonar echo. We captured the neural responses of the A1 to complex acoustic stimuli using linear, 16-channel translaminar microelectrode arrays. We analyzed 145 spectrotemporal receptive fields (STRFs) across A1, as well as the spectral and temporal modulation transfer functions (sMTF and tMTF, respectively) to determine neural tuning preferences in the spectral and temporal dimensions. We found evidence of neuronal sub-categories that were classified as having simple or complex (multi-peaked) STRFs. For simple STRFs, sMTFs and tMTFs were evaluated as a function of best frequency, and spatial location and revealed tonotopic trends similar to those reported for non-specialized animals.