TONOTOPIC ORGANIZATION OF HUMAN AUDITORY-CORTEX ANALYZED BY SPET

Single photon emission tomography (SPET) was used to map blood flow in creases in the temporal and parietal cortex of 16 normally-hearing sub jects after auditory stimulation. Eight subjects were stimulated with a multifrequency 40 dB HL pure tone at 250, 500, 1000, 2000, 4000 Hz, each frequency varying every 30 s. Single 500 Hz pure tones at 40 dB H L were delivered to the remainder of the subjects. Five bilaterally de af subjects were used as controls. Marked cerebral flow increase follo wing acoustic stimulation with a significantly prevalent activation of the contralateral temporal cortex was achieved (p < 0.001). According to the tonotopic organization of the human auditory cortex, low monof requency stimulation activated the most lateral sagittal tomograms (fr om 48.75 to 56.25 mm laterally to the brain midline) only, while multi frequency stimuli activated all sagittal tomograms (from 18.75 to 56.2 5 mm). On the basis of these results, it is likely that SPET is able t o give real information on the cortical distribution of the auditory f requency range, taking into account the number and position of the act ivated slices. Further clinical investigations in order to define the relationships among blood flow cortical increases, stimulus intensity and auditory threshold, are in progress.