Functional cerebral asymmetries of pitch processing during dichotic stimulus application: a whole-head magnetoencephalography study.

Dichotic listening (DL) studies indicate higher proficiency of the right cerebral hemisphere in processing the pitch of auditory events. Especially, acoustic stimuli of a rich harmonic structure such as square waves (complex tones) elicit a left ear advantage (LEA) under dichotic stimulus application. In order to investigate the timing of early sensory encoding at the level of the supratemporal plane, whole-head magnetoencephalography (MEG; 151 channels) recordings were performed in 20 right-handed subjects using an oddball paradigm based on dichotically applied complex tones. In contrast to electroencephalography (EEG) and event related potentials (ERP), this technique separately measures neuronal activity of left and right auditory cortex. Neuromagnetic responses were obtained both during preattentive stimulus processing, as well as during a pitch detection task. Rare stimuli presented to the left ear elicited a stronger magnetic analogue of mismatch negativity (MMNm) over both hemispheres and gave rise to shorter latencies of the contralateral mismatch fields than right ear deviants. In conclusion, the present data provide first evidence for functional laterality effects even at the level of preattentive pitch processing within the auditory cortex.