Comparison of late components in simultaneously recorded event-related electrical potentials and event-related magnetic fields.

We have attempted to define the late components of the event-related magnetic field (ERF) and to relate them to the late components of the event-related electrical potential (ERP). Simultaneous multichannel electroencephalogram (EEG) and magnetoencephalogram (MEG) were recorded in 13 subjects during an auditory oddball paradigm in two series of experiments. EEG responses to frequent tones consisted of the N1 and P2 components of the auditory vertex potential. Responses to rare tones consisted of N1, apparent P2, N2 and P3 components. All EEG components were best seen in the midline and were highly reproducible for all subjects. MEG responses to frequent tones consisted of N1m and P2m components that were highly reproducible only when recorded over the temporal region. By contrast, the ERF to rare tones was less well defined and only the N1m component could be identified satisfactorily. There was little consistent activity in the MEG at the time of occurrence of the N2 and P3 components of the ERP.