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Tinnitus is the sensation of a ringing, buzzing, roaring or hissing sound in the absence of an external sound. As tinnitus has been related to hyperactivity and synaptic plasticity changes in the central auditory system, invasive and noninvasive neuromodulation methods have been used to interfere with this underlying mechanism to reduce tinnitus loudness and distress. Recently, transcranial random noise stimulation applied over the auditory cortex induced a more pronounced effect on tinnitus loudness than transcranial direct current and alternating current stimulation. We performed tRNS over the temporoparietal cortex in 154 patients with non-pulsatile tinnitus. A total of 119 patients received low-frequency tRNS (lf-tRNS), 19 high-frequency tRNS (hf-tRNS) and 16 whole frequency spectrum tRNS (wf-tRNS). The effect was evaluated by using the numeric rating scale loudness and distress pre- and post-stimulation. This study revealed a significant reduction in tinnitus loudness when lf-tRNS and hf-tRNS were applied as well as a reduction in tinnitus-related distress with lf-tRNS. Moreover, we observed a significantly more pronounced reduction in loudness and distress in pure tone (PT) tinnitus compared to narrow band noise (NBN) tinnitus when hf-tRNS was applied, a difference that could not be obtained with lf-tRNS. Based on these results, tRNS might be a promising treatment option for non-pulsatile tinnitus; however, we cannot yet provide a clear mechanistic explanation for the different results obtained with different types of stimulation, i.e., lf-tRNS, hf-tRNS and wf-tRNS, or with different types of tinnitus, i.e., PT and NBN tinnitus.

An external auditory stimulus induces an auditory sensation which may lead to a conscious auditory perception. Although the sensory aspect is well known, it is still a question how an auditory stimulus results in an individual's conscious percept. To unravel the uncertainties concerning the neural correlates of a conscious auditory percept, event-related potentials may serve as a useful tool. In the current review we mainly wanted to shed light on the perceptual aspects of auditory processing and therefore we mainly focused on the auditory late-latency responses. Moreover, there is increasing evidence that perception is an active process in which the brain searches for the information it expects to be present, suggesting that auditory perception requires the presence of both bottom-up, i.e. sensory and top-down, i.e. prediction-driven processing. Therefore, the auditory evoked potentials will be interpreted in the context of the Bayesian brain model, in which the brain predicts which information it expects and when this will happen. The internal representation of the auditory environment will be verified by sensation samples of the environment (P50, N100). When this incoming information violates the expectation, it will induce the emission of a prediction error signal (Mismatch Negativity), activating higher-order neural networks and inducing the update of prior internal representations of the environment (P300)., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Animal research has shown that loss of normal acoustic stimulation can increase spontaneous firing in the central auditory system and induce cortical map plasticity. Enriched acoustic environment after noise trauma prevents map plasticity and abolishes neural signs of tinnitus. In humans, the tinnitus spectrum overlaps with the area of hearing loss. Based on these findings it can be hypothesized that stimulating the auditory system by presenting music compensating specifically for the hearing loss might also suppress chronic tinnitus. To verify this hypothesis, a study was conducted in three groups of tinnitus patients. One group listened just to unmodified music (i.e. active control group), one group listened to music spectrally tailored to compensate for their hearing loss, and a third group received music tailored to overcompensate for their hearing loss, associated with one (in presbycusis) or two notches (in audiometric dip) at the edge of hearing loss. Our data indicate that applying overcompensation to the hearing loss worsens the patients' tinnitus loudness, the tinnitus annoyance and their depressive feelings. No significant effects were obtained for the control group or for the compensation group. These clinical findings were associated with an increase in current density within the left dorsal anterior cingulate cortex in the alpha2 frequency band and within the left pregenual anterior cingulate cortex in beta1 and beta2 frequency band. In addition, a region of interest analysis also demonstrated an associated increase in gamma band activity in the auditory cortex after overcompensation in comparison to baseline measurements. This was, however, not the case for the control or the compensation groups. In conclusion, music therapy compensating for hearing loss is not beneficial in suppressing tinnitus, and overcompensating hearing loss actually worsens tinnitus, both clinically and electrophysiologically., (Copyright © 2012 Elsevier B.V. All rights reserved.)