Bit-mapped color imaging of human evoked potentials with reference to the N20, P22, P27 and N30 somatosensory responses.

Bit-mapped color imaging of scalp potential fields evoked by sensory stimulation in humans disclosed significant features not identified by mere inspection of multichannel traces. Methodological problems are considered in detail for early cortical SEPs which include several components with sharp rise times occurring at spatially distinct scalp locations. A manageable yet efficient imaging system requires recording electrodes in adequate number and scalp locations, bandpass fidelity to resolve slow and fast components, consistency of bioelectric input data, optimal interpolation and mapping algorithms, and consistent color scaling. Critical steps in these procedures were investigated in conjunction with new evidence on the scalp topography and neural generators of the N20, P20, P22, P27 and N30 SEP components. It is concluded that N20-P20 reflect a tangential equivalent dipole in parietal area 3b while P22 reflects a radial equivalent dipole in motor area 4.