Sensitivity of neurons in the dorsal medullary nucleus of the grassfrog to spectral and temporal characteristics of sound.

The responses of 58 dorsal medullary nucleus units to a set of spectrally and temporally structured stimuli were investigated. Responses to tonepips and noise indicated monomodal spectral sensitivities, with diverse response patterns. Phase-locking was strong for frequencies from 0.1 to 0.2 kHz, and in one unit extended up to 0.6 kHz. To clicks, amplitude modulated tonebursts and natural and artificial versions of the mating call various responses were found. Most low-frequency units fired tonically. They showed a non-selective or low-pass rate response to increasing modulation frequency, and a low-pass synchronization behavior to the envelope. A group of mid-frequency units fired phasically and exhibited a band-pass rate characteristic of amplitude modulated tonebursts. Frequently this was combined with a low-pass rate characteristic of click trains. These units hardly responded to the time-reversed mating call, but fired in a time-locked fashion to the pulses of the original mating call, up to a signal-to-noise ratio of 0 dB. This suggests that aspects of pulse envelope and interpulse interval are coded in the dorsal medullary nucleus.