The decomposition of the middle latency auditory evoked potential (MLAEP) Pa component into superficial and deep source contributions.

The results of recent investigations have suggested that the Middle Latency Auditory Evoked Potential (MLAEP) Pa component derives its physiological origins from both cortical and subcortical sources. The purpose of the present investigation was to determine if support for this hypothesis could be obtained from the off-line manipulation of the topographically recorded Pa component. The multichannel MLAEP from 15 normal hearing, neurologically intact subjects was collected following monaural left and right ear click stimulation. Data was originally collected using the linked ear reference and was subsequently re-referenced using the common average reference (CAR). These mapped data were converted off-line to source current density using the source derivation (SD) technique described by Hjorth (1975, 1980). This technique is sensitive to current activity that is generated in the superficial cerebral cortex. These SD maps of the MLAEP were subsequently subtracted from the CAR maps of the MLAEP. The derived CAR-SD maps are believed to represent that activity that is generated deep to the cerebral cortex (Hjorth and Rodin 1988). Interpretation of the mapped data have demonstrated support for the hypothesis that Pa is generated by a minimum of two systems including: 1) bilateral sources located in the posterior temporal lobes, and 2) a deeper midline generator system.