Right insulo-parietal Operculum 3 (OP3) involvement in tonal auditory phantom perception.

According to our previous fMRI study, a small region in the parietal operculum 3 (OP3) was hyperactivated as a function of tinnitus periodicity in subjects with acoustic trauma tinnitus sequelae. This region was localized in the vicinity of neural correlates of middle-ear tympano-ossicular chain movements due to pressure variations. Disturbed proprioceptors are known to trigger illusory perceptions; therefore, we hypothesized that a disturbance of middle-ear proprioceptors may originate phantom sound perceptions. We designed a 3T fMRI study that aimed to stimulate middle-ear proprioceptors by repetitive vibrations applied bilaterally using various rates of click trains. In all of the healthy subjects included in the fMRI protocol, the 30 Hz vibration rate compared to 8 Hz vibration rate, systematically triggered a clear tonal whistling tinnitus-like aftereffect tnat was perceived in both ears. We studied the neural correlates of these various stimulation and there differential aftereffects using SPM12. The fMRI neural correlates of the aftereffect inducing tinnitus were unequivocally localized in the same parietal region as in acoustic trauma tinnitus sufferers. This region is located at the insulo-parietal junction in OP3 [MNI: 42-18 22], after DARTEL acute registration this region was slightly shifted in antero-post plane [MNI: 40-13 17] but still in OP3. In addition DARTEL registration revealed an hyperactivation in the primary somatosensory cortex (area 3a/3b) in the face region [MNI: -54-13 40]. Somatosensory cortex area 3a and 3b and opercular regions are known to be involved in in proprioception and kinesthetic illusions. Activation of auditory areas were not elicited in this experiment beside the fact that subjects perceived tinnitus. Our results strongly suggest that a middle-ear kinesthetic/proprioceptive illusion exists at the origin of acoustic trauma tinnitus via a somatosensory pathway encompassing the trigeminal system. [ABSTRACT FROM AUTHOR]