Neuromagnetic responses to vowels vs. tones reveal hemispheric lateralization

To evaluate whether a simple auditory paradigm could demonstrate a difference in cortical lateralization between right- and left-handed subjects. Such information would be important for later development of clinical noninvasive tests of hemispheric language dominance in candidates for brain surgery.

Healthy subjects (10 strongly right-handed, 10 strongly left-handed, 5 weakly right-handed, and two ambidextrous) listened to binaural pairs of tones and pairs of Finnish vowels and decided whether the items in the pair were the same (target probability 20%). Cortical responses were recorded with whole-scalp magnetoencephalography.

The laterality index for strengths of the auditory-cortex 100 ms responses (N100m) to vowels vs. tones suggested left-hemispheric dominance in 8 of the 10 strongly right-handed subjects, and right-hemispheric dominance in 7 of the 10 left-handed subjects.

Our results demonstrate difference in hemispheric dominance for processing of vowels between right-handed and left-handed subjects. This difference resembles language lateralization suggested by previous invasive studies as well as by anatomical and functional comparisons in left- and right-handed subjects.

After comparison with the Wada test, this simple paradigm could prove useful as a noninvasive test for language lateralization in clinical settings.