The central acoustic tract and audio-vocal coupling in the horseshoe bat, Rhinolophus rouxi.

Abstract

Doppler shift compensation (DSC) behaviour in horseshoe bats is a remarkable example of sensorimotor feedback that stabilizes the echo frequency at the bat's optimum hearing range regardless of motion-induced frequency shifts in the echoes. Searching for a related neural interface, the nucleus of the central acoustic tract (NCAT) was investigated in the echolocating horseshoe bat, Rhinolophus rouxi, using various neurophysiological and tracer methods. The NCAT receives bilateral auditory input from the cochlear nuclei and sends projections to regions outside the classical acoustic pathway like the pretectal area or the superior colliculus. The binaural input is excitatory from the contralateral and inhibitory from the ipsilateral ear to 53% of the units, and auditory responses were biased to frontal and contralateral directions. The best frequencies of NCAT neurons match a narrow range above the main frequency component of the bat's species-specific echolocation call (62% of the units), and the neurons exhibit extremely sharp tuning (Q10dB up to 632). DSC is degraded by unilateral electrical or pharmacological microstimulation of the NCAT, and heavily impaired by unilateral lesion of the region. Altogether, the efferents of the NCAT to prevocal areas, the tuning of its neurons to the DSC-relevant echo frequency range, and the possibility to affect DSC by manipulation of the NCAT, support the assumption that the nucleus plays an important role in audio-vocal control in the horseshoe bat.