Dynamic stimulation evokes spatially focused receptive fields in bat auditory cortex.

Bats can orient and hunt for prey in complete darkness using echolocation. Due to the pulse-like character of call emission they receive a stroboscopic view of their environment. During target approach, bats adjust their emitted echolocation calls to the specific requirements of the dynamically changing environmental and behavioral context. In addition to changes of the spectro-temporal call features, the spatial focusing of the beam of the sonar emissions onto the target is a conspicuous feature during target tracking. The neural processes underlying the complex sensory-motor interactions during target tracking are not well understood. In this study, we used a two-tone-pulse paradigm with 81 combinations of inter-aural intensity differences and six inter-pulse intervals in a passive hearing task to tackle the question of how transient changes in the azimuthal position of successive sounds are encoded by neurons in the auditory cortex of the bat Phyllostomus discolor. In a population of cortical neurons (11%, 24 of 217), spatial receptive fields were focused to a small region of frontal azimuthal positions during dynamic stimulation with tone-pulse pairs at short inter-pulse intervals. The response of these neurons might be important for the behaviorally observed locking of the sonar beam onto a selected target during the later stages of target tracking. Most interestingly, the majority of these neurons (88%, 21 of 24) were located in the posterior dorsal part of the auditory cortex. This cortical subfield might thus be specifically involved in the analysis of dynamic acoustic scenes.