A hemispherically asymmetrical MEG response to vowels.

Neuromagnetic fields elicited by vowels and tones were recorded and sources were modeled as single equivalent current dipoles (ECDs) in 1 ms steps 80-400 ms post stimulus. To vowels, the left hemisphere (LH) auditory cortex had nearly twice as many satisfactory ECD fits as the right hemisphere (RH). Tones did not evoke such asymmetry. In particular, in the late field (150-400 ms) the LH had more than twice as many ECDs as the RH, and the spatial distribution of LH sources was more clustered than in the RH. An asymmetrical, focal cortical mechanism for vowel processing was identified that intensified in later auditory processing stages. These data suggest that MEG might be used for non-invasive, language laterality determination with simple vowel-like stimuli.