Neuronavigated left temporal continuous theta burst stimulation in chronic tinnitus.

PURPOSE: Clinical effects of repetitive transcranial magnetic stimulation (rTMS) in chronic tinnitus are moderate. More precise coil localisation strategies, innovative stimulation protocols, and identification of predictors for treatment response were proposed as promising attempts to enhance treatment efficacy. In this pilot study we investigated neuronavigated continuous theta burst TMS (cTBS). METHODS: Twenty-three patients received neuronavigated cTBS over the left primary auditory cortex in a randomized sham-controlled trial (verum = 12; sham = 11). Treatment response was evaluated with tinnitus questionnaires and numeric rating scales. Immediate change in numeric rating scales during the first session was used as predictor for treatment response. RESULTS: Tinnitus was significantly reduced after treatment, but there were no superior effects between verum vs. sham treatment. Immediate change in the first treatment session predicted the response to treatment only in the verum group. CONCLUSIONS: In our study, verum cTBS was not superior to sham which highlights the persistent need for improving non-invasive brain stimulation techniques for the treatment of tinnitus. Future research should focus on the transfer of positive single session effects to daily treatment trials.

Detecting tones in complex auditory scenes.

In everyday life, our auditory system is bombarded with many signals in complex auditory scenes. Limited processing capacities allow only a fraction of these signals to enter perceptual awareness. This magnetoencephalography (MEG) study used informational masking to identify the neural mechanisms that enable auditory awareness. On each trial, participants indicated whether they detected a pair of sequentially presented tones (i.e., the target) that were embedded within a multi-tone background. We analysed MEG activity for 'hits' and 'misses', separately for the first and second tones within a target pair. Comparing physically identical stimuli that were detected or missed provided insights into the neural processes underlying auditory awareness. While the first tone within a target elicited a stronger early P50m on hit trials, only the second tone evoked a negativity at 150 ms, which may index segregation of the tone pair from the multi-tone background. Notably, a later sustained deflection peaking around 300 and 500 ms (P300m) was the only component that was significantly amplified for both tones, when they were detected pointing towards its key role in perceptual awareness. Additional Dynamic Causal Modelling analyses indicated that the negativity at 150 ms underlying auditory stream segregation is mediated predominantly via changes in intrinsic connectivity within auditory cortices. By contrast, the later P300m response as a signature of perceptual awareness relies on interactions between parietal and auditory cortices. In conclusion, our results suggest that successful detection and hence auditory awareness of a two-tone pair within complex auditory scenes relies on recurrent processing between auditory and higher-order parietal cortices.

Functional near-infrared spectroscopy to probe state- and trait-like conditions in chronic tinnitus: a proof-of-principle study.

OBJECTIVE: Several neuroscience tools showed the involvement of auditory cortex in chronic tinnitus. In this proof-of-principle study we probed the capability of functional near-infrared spectroscopy (fNIRS) for the measurement of brain oxygenation in auditory cortex in dependence from chronic tinnitus and from intervention with transcranial magnetic stimulation. METHODS: Twenty-three patients received continuous theta burst stimulation over the left primary auditory cortex in a randomized sham-controlled neuronavigated trial (verum = 12; placebo = 11). Before and after treatment, sound-evoked brain oxygenation in temporal areas was measured with fNIRS. Brain oxygenation was measured once in healthy controls (n = 12). RESULTS: Sound-evoked activity in right temporal areas was increased in the patients in contrast to healthy controls. Left-sided temporal activity under the stimulated area changed over the course of the trial; high baseline oxygenation was reduced and vice versa. CONCLUSIONS: By demonstrating that rTMS interacts with auditory evoked brain activity, our results confirm earlier electrophysiological findings and indicate the sensitivity of fNIRS for detecting rTMS induced changes in brain activity. Moreover, our findings of trait- and state-related oxygenation changes indicate the potential of fNIRS for the investigation of tinnitus pathophysiology and treatment response.