Two auditory components in the 130-230 ms range disclosed by their stimulus frequency dependence

The auditory P2 wave has been studied by means of scalp potential and scalp current density (SCD) mapping. Two components were described. One, peaking around 150 ms, probably reflects a major activity in both supra temporal planes as revealed by SCD maps (P150). The other is a bilateral temporo-parietal component peaking around 220 ms (P220). These two components were functionally disclosed by their stimulus frequency dependence. The P150 potential and SCD amplitudes significantly decrease with increasing frequencies. Whereas this could be interpreted as a modulation of the neural activity, it may also be related to a tonotopical organization of the underlying generators distinct from that previously found for the N100. No frequency effect was found on P220.