Directional sensitivity of auditory neurons in the superior colliculus of the bat (Myotis lucifugus)

Abstract

The directional sensitivity of auditory neurons in the deep layers of the superior colliculus was examined in unanesthetized bats stimulated in the free field with frequency‐modulated (FM) sounds (100 to 40 kHz) mimicking their natural orientation sounds. The minimum threshold of a unit was first measured when the sound was presented directly in front of the animal. Sounds 10, 30, and 50 dB above threshold were then delivered at every 10° azimuth from a hoop‐mounted speaker that rotated along the horizontal plane from 80° ipsilateral to 80° contralateral. Many units exhibited spatial selectivity to a sound source that was restricted between 10° ipsilateral to 20° contralateral and had an intensity 10 dB above threshold. Sound of higher intensity was effective throughout the contralateral side in driving these neurons, although the relative response magnitude differed at the individual angles. Mapping experiments did not reveal any systematic representation of best azimuth in this midbrain structure. Nevertheless, faint echoes returning from a target along a line near the bat's flight path provide directional cues necessary for accurate target localization. [Work supported by NIH.]