VISUALIZATION OF CENTRAL AUDITORY PROCESS ES USING FUNCTIONAL MRI

Central auditory processes can be visualized using functional MRI in a non-invasive manner and at high spatial resolution. Acoustic stimulat ion leads to an increase of blood flow of activated areas in the plane of the superior temporal gyrus. Radiologically, this may be visualize d based on the long T-2-relaxation time of oxyhemoglobin. Patients: T en normal-hearing subjects with ages between 28 and 38 years took part in the investigations. They received binaural, monaural right, and mo naural left stimulation with pulsed sine tones of 1000 Hz at a pulse r ate of 6 Hz and a sound pressure level of 100 dB SPL. Tonotopic organi zation of the auditory cortex was visualized using stimulation by puls ed sine tones of 500Hz and 4000Hz. Results: Following monaural acousti c stimulation, increased activity of the contralateral auditory cortex could be demonstrated in 9 subjects. In one subject, bilateral activi ty was noted. Concerning the tonotopic organization of the auditory co rtex, we could show that the higher frequencies were localized more me dially and anteriorly; the lower frequencies were localized more later ally and posteriorly in the superior temporal gyrus. However, consider able overlap was noted. Conclusions: The overlap of the different freq uencies could explain the controversial discussion of the tonotopic or ganization of the auditory cortex. The results of the monaural acousti c stimulation show clearly the predominant signal increase of contrala teral areas in the primary auditory cortex. These results confirm the opinion of the current textbooks that the fiber of the auditory pathwa ys mostly cross. Further investigations using functional MRI are neces sary for better understanding of physiological and pathophysiological central-auditory processes.