Two bilateral sources of the late AEP as identified by a spatio-temporal dipole model

A new spatio-temporal dipole model is presented, which enables prediction and analysis of scalp potential wave forms due to spatio-temporal overlap of multiple generators. Each generator is thought to represent a local neural subset, the electric activity of which can be modelled by an equivalent dipole with stationary location and orientation closely related to the spatial organization of the neural subset. The temporal course of dipole magnitude is assumed to depict the external far field due to the compound discharge processes of the generator. Simulations of uni- and bilateral dipoles within the temporal lobe, oriented vertically and horizontally, demonstrate how spatio-temporal overlap mag bring about the 'vertex response' of the late AEP and the wave form changes observed over temporal sites. Analyses of late AEPs reported for a coronal chain of electrodes by Peronnet et al. (1974) and Vaughan et al. (1980) revealed that the wave forms in the 60-250 msec range could be perfectly matched at all electrodes by model wave forms due to 2 bilateral sources within the temporal lobe. Their locations, orientations and their latency difference of about 30 msec suggest consistently that the sequential activation of primary and secondary auditory cortices is the predominant source to the late AEPs.