Functional magnetic resonance imaging of auditory cortex: with special reference to the side of aural stimulation.

PURPOSE

To determine whether left- or right-side uniaural stimulation produces different fMRI activation patterns.

METHODS

Subjects were 12 volunteers (8 right-handed, 4 left-handed) with normal hearing. Functional imaging using FE-type multishot echo planar imaging was obtained in the axial plane during pure-tone and pseudoword tasks. Auditory stimuli were presented to each ear individually. In pure-tone tasks, subjects heard clustered sequences at 2000 Hz. In pseudoword tasks, subjects heard spoken Japanese syllables. The numbers of activated pixels in the auditory cortex were counted and compared for pure-tone and pseudoword tasks, as was activation according to the side of aural stimulation.

RESULTS

In right-handed subjects, prominent activation in pure-tone tasks was noted in the dominant hemisphere in 100% of cases and was unrelated to the side of the stimulation. In pseudoword tasks, prominent activation was noted on the side contralateral to the stimulus in 62.5-100% of cases. In left-handed subjects, prominent activation was noted on the side contralateral to the stimulus in both pure-tone and pseudoword tasks.

CONCLUSION

Left- and right-side stimulation produced differences in fMRI responses, especially between pure-tone and pseudoword tasks. Moreover, right-handedness and left-handedness affected results. This type of auditory fMRI may be a noninvasive indicator of language lateralization.