Wave form decomposition of 'giant SEP' and its computer model for scalp topography

By using the decomposition technique developed by ourselves to investigate the scalp topography of evoked potentials, a computer model for the scalp topography of giant SEPs was computed from 5 patients with progressive myoclonic epilepsy and was compared with those obtained from 6 normal subjects. Components of giant SEPs were similar to those of normal SEPs with respect to various parameters, although the former were much larger than the latter. An experimental enlargement of some of the early cortical components of the normal SEP model gave rise to a wave form closely resembling that of the giant SEP. These findings support our previous conclusion, derived from study of the scalp topography of the original SEP wave form, that the giant SEP results from a pathological enhancement of certain early cortical components of the normal SEP. The underlying neuronal hyperexcitability seems to involve more than one subunit of the sensorimotor cortex.