Comparison between electric evoked potentials, source dipole components and magnetic evoked fields elicited by noise/square-wave stimuli.

The aim of this study was to compare auditory evoked electric potentials (AEPs), source dipole components calculated from AEPs, and auditory evoked magnetic fields (AEFs). Noise/square-wave stimuli were presented either to the left or to the right ear. AEPs were measured from scalp electrodes on a coronal plane and AEFs were recorded over frontotemporal regions of both hemispheres. An increase of the ISI from 2 to 4-6 s did not change the scalp topography of AEPs nor the ratio of the tangential and radial source components. The 100-ms deflections of AEFs were higher in amplitude and shorter in latency to contra- than ipsilateral stimuli; a similar behaviour was seen in the tangential source components of AEPs. The similarity of the tangential components and the magnetic responses suggests that the method to calculate source dipole components can be useful in differentiating between the hemispheric differences in the activation of the auditory cortices and in discerning the tangential and the radial sources.