Peripheral and central components of alerting: habituation of acoustic startle, orienting responses, and elicited waveforms.

Behavioral orienting (OR), the acoustic startle reflex (ASR), pontogeniculooccipital (PGO) waves in the lateral geniculate body, and midlatency auditory evoked responses (MLR) represent components of alerting. The habituation rate for each was examined to test the hypothesis that OR, ASR, and PGO waves have related underlying neural mechanisms and determine the similarity in responsiveness between elicited PGO waves (PGOE) and elicited waves in the thalamic central lateral nucleus (CLE), a site that yields MLR. PGOE and CLE waves did not habituate in amplitude after 120 tones; however, the pattern of responses for each waveform was different. OR and ASR significantly decreased amplitude across trials with OR exhibiting a faster, more pronounced decrement. Some separation exists between the peripheral (OR and ASR) and central (PGOE and CLE) components of alerting. PGO and CL waves may have common underlying neural mechanisms.