Response magnitude and timing of auditory response initiation in the inferior colliculus of the awake chinchilla

Recent single-unit studies in anesthetized cats have revealed that the late ncy and strength of transient responses to tone burst stimuli are determine d largely by stimulus events in the first few ms of the signal. The present study sought to extend these findings by studying the inferior colliculus potential (ICP) in unanesthetized chinchillas. The ICP magnitude and latenc y were studied as a function of the plateau amplitude and rise time of nois e burst stimuli. ICP amplitude increased with stimulus amplitude and decrea sed with stimulus rise rime. ICP latency decreased with stimulus amplitude and increased with stimulus rise time. The absolute values of the ICP laten cies confirmed that it is only the first few ms of the stimulus which deter mine the timing of response initiation, and therefore, that it is not the p lateau level of the stimulus that directly determines the latent period. Th ese data constitute a direct link between earlier single-unit studies in an esthetized animals and brainstem-evoked potential data in animals and man. (C) 1999 Acoustical Society of America. [S0001-4966(99)03705-4].