Characterizing somatosensory evoked potential sources with dipole models: Advantages and limitations

Several methods have been developed to investigate the cerebral generators of scalp somatosensory evoked potentials (SEPs), because simple visual insp ection of the electroencephalographic signal does not allow for immediate i dentification of the active brain regions. When the neurons fired by the af ferent inputs are closely grouped, as usually occurs in SEP generation, the y can be represented as a dipole, that is, as a linear source with two oppo site poles. Several techniques for dipolar source modeling, which use diffe rent algorithms, have been employed to build source models of early, middle -latency, and late cognitive SEPs. Modifications of SEP dipolar activities after experimental maneuvers or in pathological conditions have also been o bserved. Although the effectiveness of dipolar source analysis should not b e overestimated due to the intrinsic limitations of the approach, dipole mo deling provides a means to assess SEPs in terms of cerebral sources and vol tage fields that they produce over the head. (C) 2001 John Wiley & Sons, In c.