N1 action potentials in humans: influence of simultaneous contralateral stimulation.

Nl action potentials, elicited by low-level, 4.0-kHz filtered clicks, were recorded from the ear canals of normal-hearing adults. Responses were recorded at two sensation levels in the presence and absence of a pure tone delivered to the contralateral ear. Waveforms were analysed for changes in amplitude and latency. A significant reduction in the amplitude of Nl was observed following the introduction of the contralateral tone at both FC levels. A concomitant change in latency was not observed. For all subjects, ipsilateral and contralateral signals were below the intensities which resulted in acoustic reflexes and crossover of contralateral signals. These data suggest that the Nl amplitude reduction observed in this study represents inhibitory activity of the efferent auditory pathway.