Dipole source analysis of auditory brain stem responses evoked by lateralized clicks.
The objective of this paper was to elucidate the relation between psychophysical lateralization and the neural generators of the corresponding auditory evoked potentials. Auditory brain stem responses to binaural click stimuli with different interaural time- and level differences were obtained in 12 subjects by means of multi-channel EEG recording. Data were modeled by equivalent current dipoles representing the generating sources in the brain. A generalized maximum-likelihood method was used to solve the inverse problem, taking into account the noise covariance matrix of the data. The quality of the fit was assessed by computing the goodness-of-fit as the outcome of a chi 2-test. This measure was advantageous compared to the conventionally employed residual variance. At the latency of Jewett wave V, there was a systematic variation of the moment of a rotating dipole with the lateralization of the stimulus. Dipole moment trajectories of stimuli with similar lateralization were similar. A sign reversal of the interaural differences resulted in a mirrored trajectory. Centrally-perceived stimuli corresponded to dipoles with the largest vertical components. With increasing lateralization, the vertical component of the moment decreased, while the horizontal components increased. The similarity of trajectories inducted by the same lateralization show that interaural time- and level differences are not processed independently. The present data support the notion that directional information is already extracted and represented at the level of the brain stem.
Riedel
Helmut
H
Medizinische Physik, Universität Oldenburg. helmut.riedel@uni-oldenburg.de
Kollmeier
Birger
B
D001933:Brain Stem / Q000502:physiology; D004566:Electrodes; D004594:Electrophysiology / Q000379:methods*; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D006801:Humans; D015203:Reproducibility of Results