A functional MRI study: cerebral laterality for lexical-semantic processing and human voice perception.

BACKGROUND AND PURPOSE Language dominance research using functional neuroimaging has made important contributions to clinical applications. Nevertheless, although recent neuroimaging studies demonstrated right-lateralized activation by human voice perception, the influence of voice perception in terms of language dominance has not been adequately studied. We aimed to accurately clarify language dominance for lexical-semantic processing in the temporal cortices by focusing on human voice perception. METHODS Thirty normal right-handed subjects were scanned by functional MR imaging while listening to sentences (SEN), reverse sentences (rSEN), and identifiable nonvocal sounds (SND). We investigated cerebral activation and the distribution of individual Laterality Index under 3 contrasts: rSEN-SND, SEN-SND, and SEN-rSEN. RESULTS The rSEN-SND contrast, including human voice perception, revealed right-lateralized activation in the anterior temporal cortices. Both SEN-SND and SEN-rSEN contrasts, including lexical-semantic processing, showed left-lateralized activation in the inferior and middle frontal gyrus and middle temporal gyrus. The SEN-rSEN contrast, without the influence of human voice perception, showed no temporal activation in the right hemisphere. Symmetrical or right-lateralized activation was observed in 22 of 27 subjects (81.4%) under the rSEN-SND contrast in the temporal cortices. Although 9 of 27 subjects (33.3%) showed symmetrical or right-lateralized activation under the SEN-SND contrast in the temporal cortices, all subjects showed left-lateralized activation under the SEN-rSEN contrast. CONCLUSION Our results demonstrated that right-lateralized activation by human voice perception could mask left-lateralized activation by lexical-semantic processing. This finding suggests that the influence of human voice perception should be adequately taken into account when language dominance is determined.