Neural metabolic activity in idiopathic tinnitus patients after repetitive transcranial magnetic stimulation

Aberrant brain functional network strength related to cognitive impairment in age-related hearing loss

Purpose

Age-related hearing loss (ARHL) is a major public issue that affects elderly adults. However, the neural substrates for the cognitive deficits in patients with ARHL need to be elucidated. This study aimed to explore the brain regions that show aberrant brain functional network strength related to cognitive impairment in patients with ARHL.

Methods

A total of 27 patients with ARHL and 23 well-matched healthy controls were recruited for the present study. Each subject underwent pure-tone audiometry (PTA), MRI scanning, and cognition evaluation. We analyzed the functional network strength by using degree centrality (DC) characteristics and tried to recognize key nodes that contribute significantly. Subsequent functional connectivity (FC) was analyzed using significant DC nodes as seeds.

Results

Compared with controls, patients with ARHL showed a deceased DC in the bilateral supramarginal gyrus (SMG). In addition, patients with ARHL showed enhanced DC in the left fusiform gyrus (FG) and right parahippocampal gyrus (PHG). Then, the bilateral SMGs were used as seeds for FC analysis. With the seed set at the left SMG, patients with ARHL showed decreased connectivity with the right superior temporal gyrus (STG). Moreover, the right SMG showed reduced connectivity with the right middle temporal gyrus (MTG) and increased connection with the left middle frontal gyrus (MFG) in patients with ARHL. The reduced DC in the left and right SMGs showed significant negative correlations with poorer TMT-B scores (r = -0.596, p = 0.002; r = -0.503, p = 0.012, respectively).

Conclusion

These findings enriched our understanding of the neural mechanisms underlying cognitive impairment associated with ARHL and may serve as a potential brain network biomarker for investigating and predicting cognitive difficulties.

Insight Into the Effects of Clinical Repetitive Transcranial Magnetic Stimulation on the Brain From Positron Emission Tomography and Magnetic Resonance Imaging Studies: A Narrative Review

Repetitive transcranial magnetic stimulation (rTMS) has been proposed as a therapeutic tool to alleviate symptoms for neurological and psychiatric diseases such as chronic pain, stroke, Parkinson’s disease, major depressive disorder, and others. Although the therapeutic potential of rTMS has been widely explored, the neurological basis of its effects is still not fully understood. Fortunately, the continuous development of imaging techniques has advanced our understanding of rTMS neurobiological underpinnings on the healthy and diseased brain. The objective of the current work is to summarize relevant findings from positron emission tomography (PET) and magnetic resonance imaging (MRI) techniques evaluating rTMS effects. We included studies that investigated the modulation of neurotransmission (evaluated with PET and magnetic resonance spectroscopy), brain activity (evaluated with PET), resting-state connectivity (evaluated with resting-state functional MRI), and microstructure (diffusion tensor imaging). Overall, results from imaging studies suggest that the effects of rTMS are complex and involve multiple neurotransmission systems, regions, and networks. The effects of stimulation seem to not only be dependent in the frequency used, but also in the participants characteristics such as disease progression. In patient populations, pre-stimulation evaluation was reported to predict responsiveness to stimulation, while post-stimulation neuroimaging measurements showed to be correlated with symptomatic improvement. These studies demonstrate the complexity of rTMS effects and highlight the relevance of imaging techniques.

Implications of Transcranial Magnetic Stimulation as a Treatment Modality for Tinnitus

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive, neuromodulating technique for brain hyperexcitability disorders. The objective of this paper is to discuss the mechanism of action of rTMS as well as to investigate the literature involving the application of rTMS in the treatment of tinnitus. The reviewed aspects of the protocols included baseline evaluation, the total number of sessions, frequency and the total number of stimuli, the location of treatment, and the outcome measures. Even with heterogeneous protocols, most studies utilized validated tinnitus questionnaires as baseline and outcome measures. Low frequency (1 Hz) stimulation throughout 10 consecutive sessions was the most widely used frequency and treatment duration; however, there was no consensus on the total number of stimuli necessary to achieve significant results. The auditory cortex (AC) was the most targeted location, with most studies supporting changes in neural activity with multi-site stimulation to areas in the frontal cortex (FC), particularly the dorsolateral prefrontal cortex (DLPFC). The overall efficacy across most of the reviewed trials reveals positive statistically significant results. Though rTMS has proven to impact neuroplasticity at the microscopic and clinical level, further studies are warranted to demonstrate and support the clinical use of rTMS in tinnitus treatment with a standardized protocol.

Lateralization effects in brain white matter reorganization in patients with unilateral idiopathic tinnitus: a preliminary study

Idiopathic tinnitus can cause significant auditory-related brain structural and functional changes in patients. However, changes in patterns of the lateralization effects in idiopathic tinnitus have yet to be established, especially on white matter (WM) reorganization. In this study, we studied 19 left-sided and 19 right-sided idiopathic tinnitus (LSIT, RSIT) patients and 19 healthy controls (HCs). We combined applied voxel-based morphometry (VBM) and tract-based spatial statistics (TBSS) analyses to investigate altered features of the auditory-related brain WM. We also conducted correlation analyses between the clinical variables and WM changes in the patients. Compared with the HCs, both sided tinnitus patients showed significant auditory-related brain WM alterations. More interestingly, the LSIT patients demonstrated a greater decrease in white matter volume (WMV) in the right medial superior frontal gyrus (SFG) than the RSIT; meanwhile, we also found that compared with the RSIT group, the LSIT group showed significantly increased fractional anisotropy (FA) in the body of the corpus callosum (CC), left cingulum, and right superior longitudinal fasciculus (SLF) and decreased mean diffusivity (MD) in the body of CC. Moreover, relative to the RSIT group, the LSIT group also exhibited increases in WM axial diffusivity (AD) in the left SLF, left cingulum, right middle cerebellar peduncle (MCP), left thalamus, and bilateral forceps major (FM) and decreases in radial diffusivity (RD) in the genu of CC. Additionally, the FA value of the right SLF was closely associated with tinnitus severity in the LSIT. Our study suggests that lateralization has a significant effect on WM reorganization in patients with idiopathic tinnitus; in particular, LSIT patients may experience more severe and widespread alterations in WMV and WM microstructure than the RSIT group, and all these changes are indirectly auditory related. These findings provide new useful information that can lead to a better understanding of the tinnitus mechanisms.

An updated meta-analysis: repetitive transcranial magnetic stimulation for treating tinnitus

Objective

To undertake an updated meta-analysis to obtain more evidence from randomized controlled trials (RCTs) to assess the effect of repetitive transcranial magnetic stimulation (rTMS) for the treatment of tinnitus.

Methods

PubMed®, Embase®, Web of Science, Cochrane Database of Systematic Reviews, CBM, CNKI and Wanfang were searched for RCTs from inception up to March 2020. Studies meeting the eligibility criteria were included in the meta-analysis. The mean difference was calculated and the effect size was evaluated using a Z test.

Results

The analysis included 12 randomized sham-controlled clinical trials with a total of 717 participants. Active rTMS was superior to sham rTMS in terms of the short-term and long-term effects (6 months) on the tinnitus handicap inventory scores, but an immediate effect was not significant. There was no significant immediate effect on the tinnitus questionnaire (TQ) and Beck depression inventory (BDI) scores.

Conclusions

This meta-analysis demonstrated that rTMS improved tinnitus-related symptoms, but the TQ and BDI scores demonstrated little immediate benefit. Future research should be undertaken on large samples in multi-centre settings with longer follow-up durations.