Multiple neural origins of early auditory evoked potential of rat

The multiple-origin hypothesis has been often considered for an unclear neurogenesis of a characteristic wave in various evoked potentials, none of which has been verified so far. Auditory evoked potential (AEP) in the temporal cortex of rodents has typical slow positive/negative (P1/N1) biphasic waves, which are occasionally associated with an additional 2-4-ms earlier small deflection (P0/N0). Despite previous extensive efforts, P0/N0 deflection is still discussed within the multiple-origin hypothesis. In this historical perspective, we hypothesized that observable AEP is an additive mixture of mutually temporally independent signals from different origins, and that the balance of the mixture impacts on the waveform of AEP. We attempted to verify this hypothesis for the first time by independent component analysis (ICA) of epidurally densely mapped AEPs in the primary auditory cortex of rats. The mapping showed that low amplitude AEPs tended to have more P0/N0 deflections in both pentobarbital- and ketamine/xylazine-anesthesia preparations. ICA of these AEP maps suggested that AEP consisted of at least three independent components and that the deflection appeared when subcortical contribution to AEP was equal to or larger than cortical contribution. In epicranially measured evoked potentials, subcortical and cortical contributions are mixed together because distances from electrodes to cortical sources approximate distances to subcortical sources. In such conditions, e.g. in human scalp-recording experiments or routine clinical screenings, our idea is specifically worth considering for the interpretation of signals. (C) 2007 IBRO. Published by Elsevier Ltd. All rights reserved.