Right-hemisphere dominance of phase-locked auditory evoked field components in response to periodic signals

Hertrich, I.1, Mathiak, K.2, Lutzenberger, W.2, and Ackermann, H.1
1Department of Neurology, University of Tübingen, Germany; 2MEG Center, University of Tübingen, Germany
E-mail: ingo.hertrich@uni-tuebingen.de

Psychoacoustic experiments in humans as well as various animal studies using intracranial recording procedures indicate phase-locked cortical activity to be an important aspect of complex pitch processing. In order to further elucidate the time course and hemispheric lateralization of this mechanism, human brain responses to periodic acoustic signals (repeated FM-sweeps, 2000-500 Hz; fundamental frequency F0 = 13, 22, 40, 67, or 111 Hz, duration = 300 ms) were recorded by means of whole-head magnetoencephalography (MEG) while subjects had to perform a stimulus identification task. Left- and right-hemisphere response curves were derived based on M100 dipole analysis. In accordance with previous studies, the latency of the M100 field was inversely related to F0. Furthermore, the 40-Hz stimulus elicited the smallest M100 amplitude but, in contrast, the strongest phase-locked periodic MEG activity. The phase angle of the F0 component was quite consistent across subjects in case of the three highest F0 values, indicating active synchronizing mechanisms. Phase-locked activity was significantly stronger within the right as compared to the left hemisphere. These data indicate right-hemisphere dominance of an auditory pre-processing mechanism of periodic signals, providing a framework for subsequent pitch- or event-synchronous spectral evaluation.