Roles of neural oscillation in time domain processing in the bat inferior colliculus

Abstract

Central auditory neurons in echolocating bats exhibit pulse-echo delay-tuned responses. Sullivan (1982) proposed that paradoxical latency shift (PLS), characterized by an increase in response latency to loud sounds, is important for this attribute. At present, the mechanism underlying PLS is unclear. The goal of the present study was to identify the mechanism underlying PLS. The responses of 92 neurons in the inferior colliculus of little brown bats to brief tone pulses at the unit’s CF over a wide range of sound levels were studied. Of these, 16 neurons displayed unit-specific periodic oscillatory discharges at high sound levels with a characteristic period of 1.3–6.7 ms. The 27 neurons exhibited unit-specific PLS, with quantal latency shift of 1.2–8.2 ms. In 14 neurons showing PLS, unit’s responses before, during and after iontophoretic application of bicuculline were investigated. Application of bicuculline abolished the PLS and transformed it into periodic discharges, suggesting that neural oscillation in combination with ordinary inhibition may be responsible for PLS. To further investigate whether intrinsic neural property was responsible for PLS, unit’s responses to sounds having different durations were investigated. The result indicates that both intrinsic and extrinsic mechanisms are likely involved in creation of PLS. [Work supported by NIH R01DC00663.]