, Volume 193, Issue 1, pp 13-20
Date: 18 Nov 2006

FM signals produce robust paradoxical latency shifts in the bat’s inferior colliculus

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Previous studies in echolocating bats, Myotis lucifugus, showed that paradoxical latency shift (PLS) is essential for neural computation of target range and that a number of neurons in the inferior colliculus (IC) exhibit unit-specific PLS (characterized by longer first-spike latency at higher sound levels) in response to tone pulses at the unit’s best frequency. The present study investigated whether or not frequency-modulated (FM) pulses that mimic the bat’s echolocation sonar signals were equally effective in eliciting PLS. For two-thirds of PLS neurons in the IC, both FM and tone pulses could elicit PLS, but only FM pulses consistently produced unit-specific PLS. For the remainder of PLS neurons, only FM pulses effectively elicited PLS; these cells showed either no PLS or no response, to tone pulses. PLS neurons generally showed more pronounced PLS in response to narrow-band FM (each sweeping 20 kHz in 2 ms) pulse that contained the unit’s best frequency. In addition, almost all PLS neurons showed duration-independent PLS to FM pulses, but the same units exhibited duration-dependent PLS to tone pulses. Taken together, when compared to tone pulses, FM stimuli can provide more reliable estimates of target range.