Tonotopic organization of the human auditory cortex as detected by BOLD-FMRI

Functional magnetic resonance imaging is a noninvasive and nonradioactive m ethod for the detection of focal brain activity. In the present study the a uditory cortex was investigated in nine normal subjects who were binaurally stimulated using pulsed sine tones of 500 Hz and 4000 Hz. The BOLD (blood oxygenation level dependent) signal change coincided with the stimulation p aradigm and was detected in the plane of the superior temporal gyrus. The c omparison of the spatial distribution of activated areas revealed a differe nt behavior for the two frequencies. The present findings underline the exi stence of a frequency specific organization in the medic-lateral, fi-onto-o ccipital and cranio-caudal extension in both hemispheres of the auditory co rtex in human. The activated areas for the high tone were found more fronta lly and medially orientated than the low tone stimulated areas. Furthermore , a slight cranio-caudal shift was observed for the higher frequency, more pronounced in the right than in the left temporal lobe. Finally, for most o f the subjects investigated the BOLD activation area of the 500 Hz sine ton e was larger than that of the 4000 Hz stimulation. Both frequencies showed a lateralization of signal response to the left temporal lobe. (C) 1998 Els evier Science B.V. All rights reserved.