Simultaneous recording of auditory evoked potentials. Relationships among the fast, middle and long latency components.

The whole pattern of the fast, middle and long latency auditory evoked potentials (AEP) was recorded simultaneously from the scalp surface of 13 normal-hearing adults. The individual responses were displayed on a nonlinear time axis in order to improve identification of the components. Stimulation consisted of 2048 unfiltered clicks, delivered monaurally at 80, 60, 40 dB HL with an ISI of 750 ms. Changes in mean latency and amplitude of each AEP component were statistically evaluated in relation to intensity and electrode montage (vertex-mastoid ipsi- and contralateral to the stimulated ear). The latencies of fast components I-VI and the slow P1 increase significantly with declining stimulus intensity. The amplitudes of the fast, I, II, III, V and the slow P1-N1, P2-N2 decrease significantly with intensity. As regards differences due to the electrode montage the contralateral recording causes significant changes in latency of the fast potentials up to wave IV, and changes in amplitude of the fast up to wave V, and of the slow P1-N1 and P2-N2. Therefore, as their latency and amplitude seem to be less closely related to the stimulus and electrode placement, the middle components behave differently, compared with the preceding and following components. Based on parametric comparisons of potentials ranging widely in latency, but each one evoked by an equal sensory input, this kind of AEP evaluation may be useful both for neurophysiological and clinical studies of the whole auditory pathway function.