Altered motor cortex excitability in tinnitus patients: a hint at crossmodal plasticity

Idiopathic tinnitus is a frequent and often debilitating auditory phantom perception of largely unknown pathological conditions. In electrophysiological and functional neuroimaging studies, affected subjects have shown excessive spontaneous activity in the central auditory system. To further investigate the underlying central nervous component, we assessed motor cortex excitability in 19 patients with chronic tinnitus by means of transcranial magnetic stimulation (TMS). When results were compared with data from 19 healthy controls matched for age and sex, we found significantly enhanced intracortical facilitation in tinnitus patients. These findings parallel excitability changes after limb amputation and experimental deafferentation. Our results give further support to crossmodal interactions involving neuroplastic changes in some forms of tinnitus and may help to better understand mechanisms of maladaptive cortical reorganisation involved in phantom perceptions.