TINNITUS AND EVENT-RELATED ACTIVITY OF THE AUDITORY-CORTEX

A neuromagnetic study in tinnitus patients and normal-hearing controls was performed with a modified contingent negative variation (CNV) par adigm. While the warning stimulus S1 was a tone burst at an intensity well above threshold, the imperative stimulus S2 was presented at a ne ar threshold intensity because, in the majority of cases, the perceive d loudness of tinnitus is very close to the threshold for a pure tone of the same frequency. Subjects had to respond to S2 by pressing a but ton until its offset was detected. In this case, instead of the usual sudden cut-off of the CNV after the perception of S2, a slow negative deflection develops, the post-imperative negative variation (PINV). It s initial portion probably indicates the development of a second initi al CNV because the subject had to attend also to the offset of S2. The neuromagnetic data were analysed both in the time domain and in the f requency domain (short-time spectral analysis of the classical EEG ban ds). The time domain waveform as well as the spectrotemporal patterns of the MEG bands exhibited deviations from the normal pattern in sever al tinnitus subgroups, depending on the characteristics of tinnitus (t onal vs, noisiform, monaural vs. binaural) and on the stimulation cond itions (tinnitus side vs, non-tinnitus side).