Auditory properties of the superior colliculus in the horseshoe bat, Rhinolophus rouxi

Auditory response properties were studied in the superior colliculus (SC) of the echolocating horseshoe bat Rhinolophus rouxi, a long CF-FM bat, by the use of stationary, dichotic stimuli. The most striking finding in the horseshoe bat was an enormous overrepresentation of neurons with best frequencies in the range of the constant frequency component of the species specific echolocation call (72% of the auditory neurons). These neurons had response thresholds as low as 0 dB SPL and were narrowly tuned with Q10dB--values up to 400, just as in the nuclei of the primary auditory pathway in this species. This overrepresentation may suggest the importance of the superior colliculus in the context of echolocation behavior. While noise stimuli were not particularly effective, other auditory response properties were similar to those described in other mammals. 65% of the SC neurons in the horseshoe bat responded only to monaural stimulation of one ear, primarily the contralateral one. 32% of the neurons received monaural input from both ears. The proportion of neurons responsive to ipsilateral stimulation (41%) was rather high. Mean response latency was 8.9 ms for contralateral stimulation. A tonotopic organization is lacking, but high-frequency neurons are less frequent in rostral SC.