Magnetoencephalography and late component ERPs.

The recent emergence of magnetoencephalography is a development that is already yielding results. Its intrinsic sensitivity to the actual source activity, rather than to volume currents, means that its particular value lies in source localization. As well as having proven value in research relating to early evoked response and epilepsy, biomagnetic measurements have been applied to later components. For example, results for the auditory P300 potential indicate the source to lie either in the temporal cortex or the hippocampus. More definite conclusions await further development of the instrumentation. Also, there is much scope for more sophisticated analysis of the magnetic fields, of the electric potentials, or ideally of both together. This is likely to elucidate the largely unknown functional circuitry corresponding to the late components of the response.