The overall goal of this project is to advance basic science knowledge of the ABR (Auditory Brainstem Response), recorded in humans, based upon recent developments in multi-channel recordings. Several lines of research will be pursued. First, it will be determined whether the ABR in humans, in whole or in part, can be modelled as an equivalent dipole. Humans will be studied recording from electrodes placed on the scalp according to the standard 10-20 system. Two lines of evidence will be used to determine if the potentials are consistent with an eccentric dipole generator: a) comparison of the dipole generator estimated from two different electrode arrays. b) comparison of the surface potential distribution of the ABR at each point in time, with potentials recorded from dipoles placed in a volume-conductor molded from the head of the subject. The testing of surface potential distribution related to a dipole in the internal auditory meatus will also contribute to the question as to whether wave II of the ABR is due to the VIIIth nerve action potential entering the cranium. Second, the effects of signal filters on the ABR waveforms will be studied as they affect the orientation, magnitude, or detection of the equivalent dipole. Third, the effects of muscle artifacts on the potentials recorded at different scalp locations will be determined, as well as whether nearfield muscle recordings provide a better means of excluding artifact-containing sweeps. Finally, the signal-to-noise ratio of different electrode locations for recording the ABR in humans will be studied in order to determine the optimal locations for electrodes. This research is directly related to the medical uses of the ABR, which includes diagnosis of hearing deficits in newborns, infants, and adults, as well as diagnosis of neurological abnormalities in children and adults.
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