Brain activation during dichotic presentations of consonant-vowel and musical instrument stimuli: a O-15-PET study

Dichotic listening means that two different stimuli are presented at the sa me time, one in each ear. This technique is frequently used in experimental and clinical Studies as a measure of hemispheric specialization. The prima ry aim of the present study was to record regional changes in the distribut ion of cerebral blood flow (CBF) with the O-15-PET technique to dichoticall y presented consonant-vowel (CV) and musical instrument stimuli, in order t o test the basic assumption of differential hemispheric involvement when st imuli presented to one ear dominate over stimuli presented in the other ear . All stimuli were 380 ms in duration with a 1000 ms interstimulus interval , and were presented in blocks of either CV-syllable or musical instrument pairs. Twelve normal healthy subjects had to press a button whenever they d etected a CV-syllable or a musical instrument target in a stream of CV- and musical instrument distracter stimuli. The targets appeared equally often in the right and left ear channel. The CV-syllable and musical instrument t argets activated bilateral areas in the superior temporal gyri. However, th ere were significant interactions with regard to asymmetry of the magnitude of peak activation in the significant activation clusters. The CV-syllable s resulted in greater neural activation in the left temporal lobe while the musical instruments resulted in greater neural activation in the right tem poral lobe. Within-subjects correlations between magnitude of dichotic list ening and CBF asymmetry were, however, non-significant. The changes in neur al activation were closely mimicked by the performance data which showed a right ear superiority in response accuracy for the CV-syllables, and a left ear superiority for the musical instruments. In addition to the temporal l obe activations, there were activation tendencies in the left inferior fron tal lobe, right dorsolateral prefrontal cortex, left occipital lobe, and ce rebellum. (C) 1999 Elsevier Science Ltd. All rights reserved.