Commentary: somatosensory evoked potentials and magnetic fields.

Evidence is offered for the requirement of more careful comparisons between the new event related magnetic fields of the brain (ERMFb) and their conventional counterparts the event related brain potentials (ERBP), in the somato-sensory (SEP) and auditory (AEP) modalities at least, because the existing ERBP literature contains a wealth of well-documented data on these crucial issues: (1) Contralateral and ipsilateral SEP; (2) the relevance of "background" intrinsic periodicity; and (3) the relevance of stimulus parameters, receptive fields, and subjective perceptual status to variations in the waveforms. The importance of the new 2nd derivative magnetic gradiometry for better spatiotemporal resolution of sources and for functional understanding of cerebral electrophysiology cannot be overestimated. So it may be equally important to ensure that existing, historical data from conventional scalp-conductance, systematically recorded and analyzed during the past twenty years, are not ignored at the inception of essential comparisons using complementary electromagnetic techniques.