AUDITORY INPUT TO THE PEDUNCULOPONTINE NUCLEUS .1. EVOKED-POTENTIALS

The pedunculopontine nucleus (PPN) has been implicated in sleep-wake c ontrol, arousal responses, and motor functions. The PPN also has been implicated in the generation of the P1 middle-latency auditory-evoked potential. The present study was undertaken to determine the topograph ical distribution, threshold, and response properties of depth-recorde d potentials following auditory click stimulation. Experiments were co nducted in both decerebrate cat and rat, with a view towards determini ng the presence of P1-like middle-latency auditory-evoked potentials i n the midbrain of both species. These results demonstrate a) the prese nce in and around the PPN of a P1-like potential in the decerebrate ra t similar to that described in the accompanying article as the P13 in the intact rat; b) the presence in and around the PPN of a P1-like pot ential in the decerebrate cat similar to that previously described by others as wave A in the intact cat; c) although thresholds for these p otentials were similar to those of intact preparations, following freq uencies were higher in the decerebrate preparations, i.e., responsiven ess to repetitive stimulation was higher; and d) depth-recorded somato sensory-evoked potentials also were studied in the cat and found to sh ow an evoked potential at a similar latency as middle-latency auditory depth-recorded potentials. These findings suggest that click stimulus -evoked, depth-recorded potentials are present in and around the PPN i n the decerebrate rat and cat, i.e., in the absence of cortex, at a si milar latency as in intact preparations.