Cerebral (18)F-deoxyglucose positron emission tomography (FDG-PET) has shown altered auditory pathway activity in tinnitus. However, the corresponding studies involved only small samples and analyses were restricted to the auditory cortex in most studies. Evidence is growing that also limbic, frontal, and parietal areas are involved in the pathophysiology of chronic tinnitus. These regions are considered to mediate perceptual, attentional, and emotional processes. Thus, the aim of the present study was the systematic evaluation of metabolic brain activity in a large sample of tinnitus patients. Ninety one patients with chronic tinnitus underwent FDG-PET. The effects of tinnitus severity (assessed by a tinnitus questionnaire score), duration and laterality were evaluated with statistical parametric mapping (SPM) in whole brain analyses. In addition, region of interest analyses were performed for primary auditory areas. Tinnitus duration correlated positively with brain metabolism in right inferior frontal, right ventro-medial prefrontal, and right posterior cingulate cortex. Tinnitus distress correlated positively with activation of left and right posterior inferior temporal gyrus as well as left and right posterior parahippocampal-hippocampal interface. Region of interest analysis demonstrated an overactivation of left in contrast to right Heschl's gyrus independently from tinnitus laterality and anatomical hemispheric differences. Tinnitus duration and distress were associated with areas involved in attentional and emotional processing. This is in line with recent findings indicating the relevance of higher order areas in the pathophysiology of tinnitus. Earlier results of asymmetric activation of the auditory cortices in tinnitus were confirmed, i.e., left-sided overactivation was found independently from tinnitus laterality.
Tinnitus is the perception of sound in the absence of an environmental sound source. Abnormal activity in central auditory pathways is considered as the neuronal correlate of tinnitus. However, there is increasing evidence from neuroimaging studies for an additional involvement of the frontal cortex in the pathophysiology of tinnitus, especially concerning its attentional and emotional aspects. Recently, in a subgroup of tinnitus patients, temporary reduction of tinnitus intensity and tinnitus-related distress has been reported after bifrontal tDCS with the anode over the right and the cathode over the left dorsolateral prefrontal cortex (DLPFC). The aim of this study was to investigate whether repeated application of bifrontal tDCS results in longer-lasting reduction of tinnitus and may represent a potential treatment approach. Thirty-two patients with chronic and treatment-resistant tinnitus received six sessions of bifrontal tDCS (1.5 mA, 30 min, two sessions per week) with the anode over the right and the cathode over the left DLPFC. Treatment outcome was assessed with several standardized tinnitus questionnaires, numeric rating scales, and a depression scale. In the entire group, beneficial effects of bifrontal tDCS on tinnitus were found for numeric rating scores of loudness, unpleasantness, and discomfort, but not in tinnitus or depression scales. Exploratory analysis revealed an effect of gender on treatment effects with female patients demonstrating a better response in several scores. Our open-label pilot study suggests some beneficial effect of bifrontal tDCS (anode right and cathode left) in the treatment of severe tinnitus, warranting further controlled studies.
Background: Vagus nerve stimulation has been successfully used as a treatment strategy for epilepsy and affective disorders for years. Transcutaneous vagus nerve stimulation (tVNS) is a new non-invasive method to stimulate the vagus nerve, which has been shown to modulate neuronal activity in distinct brain areas. Objectives: Here we report effects of tVNS on cardiac function from a pilot study, which was conducted to evaluate the feasibility and safety of tVNS for the treatment of chronic tinnitus. Methods: Twenty-four patients with chronic tinnitus underwent treatment with tVNS over 3–10 weeks in an open single-armed pilot study. Safety criteria and practical usability of the neurostimulating device were to investigate by clinical examination and electrocardiography at baseline and at several visits during and after tVNS treatment (week 2, 4, 8, 16, and 24). Results: Two adverse cardiac events (one classified as a severe adverse event) were registered but considered very unlikely to have been caused by the tVNS device. Retrospective analyses of electrocardiographic parameters revealed a trend toward shortening of the QRS complex after tVNS. Conclusion: To our knowledge this is one of the first studies investigating feasibility and safety of tVNS in a clinical sample. In those subjects with no known pre-existing cardiac pathology, preliminary data do not indicate arrhythmic effects of tVNS.
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