GENERATORS OF THE BRAIN-STEM AUDITORY-EVOKED POTENTIAL IN CAT .3. IDENTIFIED CELL-POPULATIONS

This paper examines the relationship between different brainstem cell populations and the brainstem auditory evoked potential (BAEP), First, we present a mathematical model relating the BAEP to underlying cellu lar activity, Then, we identify specific cellular generators of the cl ick-evoked BAEP in cats by combining model-derived insights with key e xperimental data. These data include (a) a correspondence between part icular brainstem regions and specific extrema in the BAEP waveform, de termined from lesion experiments, and (b) values for model parameters derived from published physiological and anatomical information, Ultim ately, we conclude (with varying degrees of confidence) that: (1) the earliest extrema in the BAEP are generated by spiral ganglion cells, ( 2) P2 is mainly generated by cochlear nucleus (CN) globular cells, (3) P3 is partly generated by CN spherical cells and partly by cells rece iving inputs from globular cells, (4) P4 is predominantly generated by medial superior olive (MSG) principal cells, which are driven by sphe rical cells, (5) the generators of P5 are driven by MSO principal cell s, and (6) the BAEP, as a whole, is generated mainly by cells with cha racteristic frequencies above 2 kHz, Thus, the BAEP in cats mainly ref lects cellular activity in two parallel pathways, one originating with globular cells and the other with spherical cells, Since the globular cell pathway is poorly represented in humans, we suggest that the hum an BAEP is largely generated by brainstem cells in the spherical cell pathway. Given our conclusions, it should now be possible to relate ac tivity in specific cell populations to psychophysical performance sinc e the BAEP can be recorded in behaving humans and animals.