Functional asymmetry in human primary auditory cortex: identified from longitudinal fMRI study.

The leftward hemispheric dominance in language processing may be associated with fundamental functional asymmetry in the primary auditory cortex (PAC). Based on repeated functional MRI (fMRI) measurements, we investigated the presence of functional asymmetry in the human PAC using binaural presentation of linguistic sounds (two-syllable nouns) and simple tonal stimulation. Eight right-handed volunteers underwent nine fMRI sessions, approximately eight weeks apart, spanning the duration of more than a year. The PAC from each hemisphere was manually segmented and the volume of activation, detected within the segmented region-of-interest, was measured across the subjects and sessions to generate functional laterality indices. Although variations existed in activation volume between sessions and subjects, we found predominant and consistent leftward functional asymmetry in PAC during both linguistic and non-linguistic sound stimulations.