The decomposition of the Middle Latency Auditory Evoked Potential (MLAEP) Pa component into superficial and deep source contributions

Abstract

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.

The development of auditory event related potentials in the rhesus monkey(Macaca mulatta)

“…Those peaks may be homologous to the human MLR Po and Pa. The generator of Pa in humans is the posterior temporal lobe (Deiber, Ibanez, Fischer, Perrin, & Mauguierre, 1988;Jacobson & Newman, 1990;Lee et al, 1984;Scherg & von Cramon, 1986; see Kraus, McGee, & Stein, 1994 for a review). The improvement in reproducibility in MLRs and AEPs with age is consistent with a peripheral to central developmental trajectory in the auditory system.…”

Normal Hearing Young Adults with Mild Tinnitus: Reduced Inhibition as Measured Through Sensory Gating

“…The Pa component, to our knowledge, has not been studied extensively as a mechanism of gating function, but has been reported to reflect amplitude suppression in healthy controls 25 as well as a lack of suppression in patients with damage to prefrontal cortex. 8 Research indicates that this component arises from generators in auditory cortex and deeper cortical structures, 26 although the anatomical sources, especially involved in gating-related inhibitory processes, remain unclear. Our laboratory is currently conducting source analyses to determine whether decreased inhibition may be visualized through group differences in cortical network activation.…”

Effects of Stimulus Rate and Gender on the Auditory Middle Latency Response

“…It is important for clinicians to understand the underlying neural generators contributing to individual AMLR components when selecting appropriate test protocols that may optimize either the Pa or the Pb waveforms. Previous researchers have hypothesized that Pa primarily arises from the telencephalon (tangentially oriented dipole sources within the posterior temporallobe), with some influence from deep midline generators in the brain stem (Woods et aI, 1987;Cacace et aI, 1990;Jacobson and Newman, 1990). In contrast, wave Pb primarily arises from the diencephalon, midbrain, and thalamic portions of the reticular activating system (Buchwald et aI, 1981;Erwin and Buchwald 1986;Harrison et aI, 1990).…”