Enhancing neurosteroid synthesis--relationship to the pharmacology of translocator protein (18 kDa) (TSPO) ligands and benzodiazepines

INTRODUCTION

The treatment of anxiety disorders is still a challenge; novel pharmacological approaches that combine rapid anxiolytic efficacy with fewer side effects are needed. A promising target for such compounds is the mitochondrial translocator protein (18 kDa) (TSPO). TSPO plays an important role for the synthesis of neurosteroids, known to modulate GABAA receptors, thereby exerting anxiolytic effects.

METHODS

We investigated the pharmacological profile of 2 well established TSPO ligands (XBD173 and etifoxine) compared to the benzodiazepine diazepam with regard to TSPO binding affinity, TSPO expression and neurosteroidogenesis.

RESULTS

In BV-2 microglia and C6 glioma cells all compounds significantly enhanced TSPO protein expression. Radioligand binding assays revealed the highest binding affinity to TSPO for XBD173, followed by diazepam and etifoxine. Pregnenolone synthesis was most potently enhanced by etifoxine.

DISCUSSION

Etifoxine turned out to be the most potent enhancer of neurosteroidogenesis, although its binding affinity to TSPO was lowest. These results indicate that the efficacy of TSPO ligands to stimulate neurosteroid synthesis, thereby leading to anxiolytic effects cannot be concluded from their binding affinity to TSPO.

Sexual motivation is reflected by stimulus-dependent motor cortex excitability

Sexual behavior involves motivational processes. Findings from both animal models and neuroimaging in humans suggest that the recruitment of neural motor networks is an integral part of the sexual response. However, no study so far has directly linked sexual motivation to physiologically measurable changes in cerebral motor systems in humans. Using transcranial magnetic stimulation in hetero- and homosexual men, we here show that sexual motivation modulates cortical excitability. More specifically, our results demonstrate that visual sexual stimuli corresponding with one's sexual orientation, compared with non-corresponding visual sexual stimuli, increase the excitability of the motor cortex. The reflection of sexual motivation in motor cortex excitability provides evidence for motor preparation processes in sexual behavior in humans. Moreover, such interrelationship links theoretical models and previous neuroimaging findings of sexual behavior.

Bilateral prefrontal rTMS and theta burst TMS as an add-on treatment for depression: a randomized placebo controlled trial

OBJECTIVES

Repetitive transcranial magnetic stimulation (rTMS) of the left dorsolateral-prefrontal cortex (DLPFC) exerts antidepressant effects. In this randomised controlled clinical trial we aimed to test the safety and therapeutic efficacy of bilateral theta-burst stimulation (TBS) as an add-on therapy to standard treatment of major depression.

METHODS

Fifty-six patients diagnosed with a moderate to severe depressive episode received 15 daily treatments of either rTMS (110% motor-threshold; rightDLPFC, 1000 stimuli at 1 Hz + leftDLPFC, 1000 stimuli at 10 Hz), theta-burst stimulation (80% motor-threshold; rightDLPFC, continuous TBS, 1200 stimuli + leftDLPFC, intermittent TBS, 1200 stimuli), or sham TMS (N = 17, sham coil with the TBS protocol).

RESULTS

There was no significant effect in the primary outcome measures (change of the 21-item Hamilton Rating Scale for Depression). However, there was a tendency towards an increased responder rate at the end of the follow-up period for both active treatments as compared to sham, and this tendency was most pronounced for the TBS group.

CONCLUSIONS

This pilot study did not reveal significant advantages of bilateral TBS or rTMS over sham treatment as an add-on treatment for major depression. A tendency towards a superior effect of bilateral TBS at the end of the follow-up period may warrant further studies.

The ACDC pilot trial: targeting the anterior cingulate by double cone coil rTMS for the treatment of depression

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) of the dorsolateral-prefrontal cortex (DLPFC) with conventional figure-of-8 (=butterfly) coils has been used as an antidepressant therapeutic tool for almost twenty years. Very recently, an innovative rTMS coil, the so-called double cone coil (DC), was introduced allowing the modulation of the anterior cingulate cortex (AC). We investigated safety and therapeutic effectiveness of this stimulation in a naturalistic clinical setting.

METHOD

Forty-five patients suffering a moderate to severe depressive episode were randomized to receive 15 sessions of either conventional rTMS of the left DLPFC ("butterfly-rTMS"; 10 Hz; 2000 stimuli/day, RMT 110%), mediofrontal double cone coil stimulation of the anterior cingulate cortex ("ACDC-rTMS" with equal parameters), or sham-stimulation. The primary outcome was the change in the 21-items Hamilton Rating Scale for Depression (HAMD) from baseline to the end of treatment. Secondary outcome measures were changes over the course of the trial regarding the HAMD, the Beck Depression Inventory (BDI), the Clinical Global Impression (CGI) and the Global Assessment of Functioning (GAF) scales.

RESULTS

There was a significant group × time interaction effect regarding the primary outcome (F = 3.269; df = 2,37; P = 0.049). Post-hoc t-testing revealed a significant effect for the comparison ACDC vs. butterfly at week 3/end of treatment (T = 2.646; df = 26; P = 0.014). No severe adverse events occurred during the study. ACDC-stimulation was well tolerated by the majority of patients similar like butterfly-rTMS and sham-stimulation.

CONCLUSION

This pilot study demonstrated the feasibility of ACDC-rTMS-stimulation as an add-on-treatment for depression. Its clinical effects warrant further investigation in the future.

Gender-specific association of variants in the AKR1C1 gene with dimensional anxiety in patients with panic disorder: additional evidence for the importance of neurosteroids in anxiety?

BACKGROUND

Neurosteroids are synthesized both in brain and peripheral steroidogenic tissue from cholesterol or steroidal precursors. Neurosteroids have been shown to be implicated in neural proliferation, differentiation, and activity. Preclinical and clinical studies also suggest a modulatory role of neurosteroids in anxiety-related phenotypes. However, little is known about the contribution of genetic variants in genes relevant for the neurosteroidogenesis to anxiety disorders.

METHODS

We performed an association analysis of single nucleotide polymorphisms (SNPs) in five genes related to the neurosteroidal pathway with emphasis on progesterone and allopregnanolone biosynthesis (steroid-5-alpha-reductase 1A (SRD5A1), aldo-keto reductase family 1 C1-C3 (AKR1C1-AKR1C3) and translocator protein 18 kDA (TSPO) with panic disorder (PD) and dimensional anxiety in two German PD samples (cases N = 522, controls N = 1,115).

RESULTS

Case-control analysis for PD and SNPs in the five selected genes was negative in the combined sample. However, we detected a significant association of anticipatory anxiety with two intronic SNPs (rs3930965, rs41314625) located in the gene AKR1C1 surviving correction for multiple testing in PD patients. Stratification analysis for gender revealed a female-specific effect of the associations of both SNPs.

CONCLUSIONS

These results suggest a modulatory effect of AKR1C1 activity on anxiety levels, most likely through changes in progesterone and allopregnanolone levels within and outside the brain. In summary, this is the first evidence for the gender-specific implication of the AKR1C1 gene in the expression of anticipatory anxiety in PD. Further analyses to unravel the functional role of the SNPs detected here and replication analyses are needed to validate our results.

Me or you? Neural correlates of moral reasoning in everyday conflict situations in adolescents and adults

Throughout adolescence, progress in the understanding of the moral domain as well as changes in moral behavior is observable. We tested 16 adolescents (14-16 years of age) and 16 healthy adults (22-31 years of age) on the developmental changes in everyday moral decision making using functional magnetic resonance imaging (fMRI). Using verbal stories describing everyday moral conflict situations, subjects had to decide between a moral standard or a personal desire. In the moral conflict situations, adolescents not only chose significantly more often the hedonistic alternative than adults, but they also reported higher certainty ratings. Contrasted with everyday social conflict situations that required a decision between a social-oriented behavior and a personal need, moral conflict situations induced an activity increase in frontal areas, the middle temporal gyrus, the thalamus, and the parahippocampal gyrus in adolescents compared to adults. Moreover, a closer look at the moral conflict situations revealed that adolescents showed more activity than adults in brain areas that are also centrally involved in theory of mind (ToM) during morally oriented decisions in contrast to personal-oriented decisions. This indicated that the development of moral reasoning may be strongly correlated with the development of ToM reasoning.

Feasibility, safety and efficacy of transcutaneous vagus nerve stimulation in chronic tinnitus: an open pilot study

OBJECTIVES

Vagus nerve stimulation represents an established treatment strategy for epilepsy and affective disorders. Recently, positive effects were also shown in animals and humans with tinnitus. Here we report the results of an open pilot study exploring feasibility, safety and efficacy of tVNS in the treatment of chronic tinnitus.

STUDY DESIGN

Fifty patients with chronic tinnitus underwent tVNS in an open single-armed pilot study which was conducted in two phases applying two different stimulating devices (Cerbomed CM02 and NEMOS). Clinical assessment was based on Tinnitus Questionnaire (TQ), Tinnitus Handicap Inventory (THI), Beck Depression Inventory (BDI), WHO Quality of Life, and various numeric rating scales. Primary outcome was defined as change in TQ (baseline vs. final visit in week 24). The study has been registered with clinicaltrials.gov (NCT01176734).

RESULTS

Primary analysis indicated mean TQ reductions of 3.7 points (phase 1) and 2.8 points (phase 2) significant for the first study phase. Secondary analyses indicated a significant BDI reduction for phase 1 (uncorrected for multiple testing), but no further systematic or significant effects. Adverse events included twitching and pressure at electrode placement site. The occurrence of one hospitalization because of palpations and the development of a left bundle branch block were considered as unrelated to the intervention. Cognitive testing revealed no significant changes.

CONCLUSION

Our data demonstrate the feasibility of tVNS over a period of 6 months. There was no clinically relevant improvement of tinnitus complaints. Our data suggest tVNS to be considered safe in patients without a history of cardiac disease.

Changes in motor cortex excitability associated with temporal repetitive transcranial magnetic stimulation in tinnitus: hints for cross-modal plasticity?

BACKGROUND

Motor cortex excitability was found to be changed after repetitive transcranial magnetic stimulation (rTMS) of the temporal cortex highlighting the occurrence of cross-modal plasticity in non-invasive brain stimulation. Here, we investigated the effects of temporal low-frequency rTMS on motor cortex plasticity in a large sample of tinnitus patients. In 116 patients with chronic tinnitus different parameters of cortical excitability were assessed before and after ten rTMS treatment sessions. Patients received one of three different protocols all including 1 Hz rTMS over the left temporal cortex. Treatment response was defined as improvement by at least five points in the tinnitus questionnaire (TQ). Variables of interest were resting motor threshold (RMT), short-interval intra-cortical inhibition (SICI), intracortical facilitation (ICF), and cortical silent period (CSP).

RESULTS

After rTMS treatment RMT was decreased by about 1% of stimulator output near-significantly in the whole group of patients. SICI was associated with significant changes with respect to treatment response. The group of treatment responders showed a decrease of SICI over the course of treatment, the group of non-responders the reverse pattern.

CONCLUSIONS

Minor RMT changes during rTMS treatment do not necessarily suggest the need for systematic re-examination of the RMT for safety and efficacy issues. Treatment response to rTMS was shown to be related to changes in SICI that might reflect modulation of GABAergic mechanisms directly or indirectly related to rTMS treatment effects.

Structural brain changes following left temporal low-frequency rTMS in patients with subjective tinnitus

Repetitive transcranial magnetic stimulation (rTMS) of the temporal cortex has been used to treat patients with subjective tinnitus. While rTMS is known to induce morphological changes in healthy subjects, no study has investigated yet whether rTMS treatment induces grey matter (GM) changes in tinnitus patients as well, whether these changes are correlated with treatment success, and whether GM at baseline is a useful predictor for treatment outcome. Therefore, we examined magnetic resonance images of 77 tinnitus patients who were treated with rTMS of the left temporal cortex (10 days, 2000 stimuli/day, 1 Hz). At baseline and after the last treatment session high-resolution structural images of the brain were acquired and tinnitus severity was assessed. For a subgroup of 41 patients, additional brain scans were done after a follow-up period of 90 days. GM changes were analysed by means of voxel based morphometry. Transient GM decreases were detectable in several brain regions, especially in the insula and the inferior frontal cortex. These changes were not related to treatment outcome though. Baseline images correlated with change in tinnitus severity in the frontal cortex and the lingual gyrus, suggesting that GM at baseline might hold potential as a possible predictor for treatment outcome.

Antipsychotic treatment with quetiapine increases the cortical silent period

RATIONALE

Measurement of motor cortex excitability with single and paired pulse transcranial magnetic stimulation has become an established method for in vivo characterization of the effects of central-acting drugs. The comparison of drug-free and medicated patients with schizophrenia suggests an association of neuroleptics intake and prolongation of the cortical silent period (CSP). However all available data come from cross-sectional non-randomized studies. Thus it is not clear whether the observed difference is an effect of medication or reflects differences in disease severity or both.

OBJECTIVES

We aimed to investigate whether the CSP or other parameters of cortical excitability change, when cortical excitability is measured in drug-free patients with acute psychosis before and after 3week intake of the atypical neuroleptic quetiapine.

METHODS

Different parameters of cortical excitability were studied in 24 drug-free patients with acute psychosis before and after 3weeks of treatment with a mean dose of 352±199mg quetiapine.

RESULTS

We observed a significant prolongation of the cortical silent period (CSP) after three week treatment with quetiapine. Other parameters of cortical excitability such as motor threshold (MT), short intracortical inhibition (SICI) and intracortical facilitation (ICF) remained unaffected. There was a significant improvement in clinical parameters (PANS, GAF) but no significant correlation between clinical improvement and changes in cortical excitability.

CONCLUSIONS

These longitudinal data are in line with previous reports from cross-sectional studies. The excitability changes induced by three-week intake of quetiapine in acute psychotic patients confirm the notion that neuroleptic treatment is associated with an increase in CSP.

The influence of Hatha yoga as an add-on treatment in major depression on hypothalamic-pituitary-adrenal-axis activity: a randomized trial

OBJECTIVES

The impact of Hatha yoga as add-on treatment to quetiapine fumarate extended release (QXR) or escitalopram (ESC) in depressed patients on hypothalamic-pituitary-adrenal (HPA) axis activity was assessed.

METHODS

60 inpatients suffering from major depressive disorder (MDD) according to DSM-IV were randomized for a 5 week treatment with Yoga or not (control group) and with either QXR (300 mg/day) or ESC (10 mg/day). Serial dexamethasone/corticotropin releasing hormone (DEX/CRH) tests were performed to assess HPA axis function. The Hamilton Depression Rating Scale (21-HAMD) was used weekly.

RESULTS

A more pronounced down regulation of the HPA axis activity due to yoga could not be detected. The stepwise long term cortisol reduction was seen in both medication groups, irrespectively of yoga add-on treatment. In addition, cortisol improvers in week 1 of therapy (reduction in cortisol peak value within the DEX/CRH test) reached significant greater amelioration of depressive symptoms after 5 weeks.

CONCLUSIONS

Our results suggest that antidepressant agents down regulate HPA axis function to a greater extent than additional Hatha yoga treatment. Moreover, an early reduction of HPA system hyperactivity after one week of pharmacological treatment seems to raise the possibility of a favorable treatment response.

Effects of escitalopram/quetiapine combination therapy versus escitalopram monotherapy on hypothalamic-pituitary-adrenal-axis activity in relation to antidepressant effectiveness

The hypothalamic-pituitary-adrenocortical (HPA) system is believed to play an important role in the pathophysiology of major depressive disorder. In this context, the atypical antipsychotic quetiapine (QUE) has been shown to inhibit HPA system activity in healthy subjects. In this study we investigated whether the putative inhibitory effects of QUE on HPA system activity may contribute to its antidepressant efficacy. We analyzed the effects of QUE as an augmentation to the selective serotonin reuptake inhibitor (SSRI) escitalopram (ESC) on HPA system activity in comparison to a monotherapy with ESC in relation to the antidepressant effectiveness. HPA axis activity (cortisol and ACTH) was measured by means of the dexamethasone/corticotropin-releasing hormone (DEX/CRH) test which was performed before (week 0) and during (week 1, week 5) antidepressant psychopharmacotherapy. The combination therapy, but not the ESC monotherapy showed significantly inhibiting effects on HPA system activity leading to stepwise down-regulation. ACTH concentrations were reduced in the ESC/QUE group during five weeks of treatment. The inhibitory effect of QUE maybe involved in its antidepressant effects as an augmentation strategy.

Talking to the synapse: how antidepressants can target glial cells to reshape brain circuits

Functional alterations in synaptic contacts in specific brain areas are a hallmark of major depressive disorder (MDD). Antidepressant treatments not only readjust the aberrant concentrations of neurotransmitters in the synaptic clefts, but have the capacity to reshape neuronal circuits by affecting synaptogenesis and synaptic stabilization in specific regions of the brain. Nevertheless, the underlying molecular mechanisms are still unclear. Glial cells are active partners of neurons in orchestrating molecular signals that regulate the arrangement of neuronal circuits both in the developing and adult brain. Here, we present evidences indicating that glial cells might be substrates of antidepressant action for restructuring neuronal networks that has become miswired after the onset or progression of MDD. We aim to offer an alternative approach (a "gliocentric" view) to study this complex neuropsychiatric disorder and to identify alternative mechanisms of action for the currently available antidepressant therapies. Such knowledge may help to improve current treatment regimens or identify novel targets for the development of more efficacious antidepressant drugs.

Translocator protein (18 kDa) (TSPO) is expressed in reactive retinal microglia and modulates microglial inflammation and phagocytosis

BACKGROUND

The translocator protein (18 kDa) (TSPO) is a mitochondrial protein expressed on reactive glial cells and a biomarker for gliosis in the brain. TSPO ligands have been shown to reduce neuroinflammation in several mouse models of neurodegeneration. Here, we analyzed TSPO expression in mouse and human retinal microglia and studied the effects of the TSPO ligand XBD173 on microglial functions.

METHODS

TSPO protein analyses were performed in retinoschisin-deficient mouse retinas and human retinas. Lipopolysaccharide (LPS)-challenged BV-2 microglial cells were treated with XBD173 and TSPO shRNAs in vitro and pro-inflammatory markers were determined by qRT-PCR. The migration potential of microglia was determined with wound healing assays and the proliferation was studied with Fluorescence Activated Cell Sorting (FACS) analysis. Microglial neurotoxicity was estimated by nitrite measurement and quantification of caspase 3/7 levels in 661 W photoreceptors cultured in the presence of microglia-conditioned medium. The effects of XBD173 on filopodia formation and phagocytosis were analyzed in BV-2 cells and human induced pluripotent stem (iPS) cell-derived microglia (iPSdM). The morphology of microglia was quantified in mouse retinal explants treated with XBD173.

RESULTS

TSPO was strongly up-regulated in microglial cells of the dystrophic mouse retina and also co-localized with microglia in human retinas. Constitutive TSPO expression was high in the early postnatal Day 3 mouse retina and declined to low levels in the adult tissue. TSPO mRNA and protein were also strongly induced in LPS-challenged BV-2 microglia while the TSPO ligand XBD173 efficiently suppressed transcription of the pro-inflammatory marker genes chemokine (C-C motif) ligand 2 (CCL2), interleukin 6 (IL6) and inducible nitric oxide (NO)-synthase (iNOS). Moreover, treatment with XBD173 significantly reduced the migratory capacity and proliferation of microglia, their level of NO secretion and their neurotoxic activity on 661 W photoreceptor cells. Furthermore, XBD173 treatment of murine and human microglial cells promoted the formation of filopodia and increased their phagocytic capacity to ingest latex beads or photoreceptor debris. Finally, treatment with XBD173 reversed the amoeboid alerted phenotype of microglial cells in explanted organotypic mouse retinal cultures after challenge with LPS.

CONCLUSIONS

These findings suggest that TSPO is highly expressed in reactive retinal microglia and a promising target to control microglial reactivity during retinal degeneration.

State- and trait-related alterations of motor cortex excitability in tinnitus patients

Chronic tinnitus is a brain network disorder with involvement of auditory and non-auditory areas. Repetitive transcranial magnetic stimulation (rTMS) over the temporal cortex has been investigated for the treatment of tinnitus. Several small studies suggest that motor cortex excitability is altered in people with tinnitus. We retrospectively analysed data from 231 patients with chronic tinnitus and 120 healthy controls by pooling data from different studies. Variables of interest were resting motor threshold (RMT), short-interval intra-cortical inhibition (SICI), intra-cortical facilitation (ICF), and cortical silent period (CSP). 118 patients were tested twice - before and after ten rTMS treatment sessions over the left temporal cortex. In tinnitus patients SICI and ICF were increased and CSP was shortened as compared to healthy controls. There was no group difference in RMT. Treatment related amelioration of tinnitus symptoms were correlated with normalisations in SICI. These findings confirm earlier studies of abnormal motor cortex excitability in tinnitus patients. Moreover our longitudinal data suggest that altered SICI may reflect a state parameter, whereas CSP and ICF may rather mirror a trait-like predisposing factor of tinnitus. These findings are new and innovative as they enlarge the knowledge about basic physiologic and neuroplastic processes in tinnitus.

Impact on cortisol and antidepressant efficacy of quetiapine and escitalopram in depression

BACKGROUND

In this study, the impact of quetiapine fumarate extended release (QXR) and escitalopram (ESC) on HPA axis activity was investigated in depressed patients in relationship to antidepressant efficacy.

METHODS

In a randomized, open-label 5-week trial 60 inpatients suffering from major depression (DSM-IV criteria) were treated for 5 weeks with either QXR (300 mg/day) or ESC (10mg/day). The dexamethasone/CRH (DEX/CRH) test was performed before treatment, after 1, and after 5 weeks of treatment. Cortisol (COR) AUC values were used to assess HPA axis function. The Hamilton Depression Rating Scale was used weekly to estimate antidepressant efficacy.

RESULTS

QXR and ESC showed comparable antidepressant effects but strongly differed in their impact on HPA axis activity. In the QXR group, a marked inhibition of COR AUC levels was observed which was most pronounced after one week of treatment but showed a partial re-increase after 5 weeks of treatment. In contrast, ESC transiently stimulated COR AUC values (week 1) whereas COR AUC levels at week 0 and week 5 were comparable. COR improvement at week 1 (defined as COR peak value reduction between DEX/CRH test 1 and 2) was significantly associated with better clinical outcome.

CONCLUSION

Apparently, different effects on HPA axis activity reflect distinct pharmacoendocrinological properties of psychotropic drugs.

Functional activity and effective connectivity of the posterior medial prefrontal cortex during processing of incongruent mental states

The neurocognitive components of Theory of Mind reasoning remain poorly understood. In particular the role of the posterior medial prefrontal cortex in the processing of other's mental states such as beliefs that are incongruent with one's own knowledge of reality is not clear-cut. It is unknown whether this region is involved in computing discrepant mental states or in subsequently resolving a response conflict between the discrepant others' and one's own beliefs. To test this, we adapted a false belief paradigm for the separate inspection of functional brain activity related to (1) the computation of diverging beliefs and (2) the subsequent consideration and selection of another's or one's own belief. Based on statistical parametric findings from functional neuroimaging, we employed dynamic causal modelling combined with Bayesian model selection to further characterize the interplay of resulting brain regions. In the initial computation of diverging beliefs, the posterior medial prefrontal cortex (pMPFC) and the bilateral temporoparietal cortex were crucially involved. The findings suggest that the bilateral temporal cortex engages in the construction and adjustment of diverging mental states by encoding relevant environmental information. The pMPFC inhibits this stimulus-bound processing which helps to compute discrepant mental states and process another's false belief decoupled from one's own perception of reality. In the subsequent question phase the right temporoparietal cortex showed increased activity related to switching to and reconsidering another's beliefs in order to select the correct response.

Targeting glia cells: novel perspectives for the treatment of neuropsychiatric diseases

Neuropsychiatric disorders are devastating mental illnesses with a high economic burden. The additional morbidity associated with social issues that arises along with the course of these diseases increases the need for a clear understanding of their etiopathogenesis to allow an implementation of novel pharmacological strategies. Yet a poor knowledge about interactions occurring at the glia-neuron interface in health and disease still hampers innovative discoveries, despite the fact that glia cells have been long described to actively participate in the regulation of brain circuits.

The purpose of this review was to collect the scattered literature on the involvement of glia cells in neuropsychiatric disorders and to describe how also these cells besides neurons might be responsive to current pharmacological interventions. We hope thereby to offer alternative approaches for investigations that may open avenues to search for new potential targets for drug discovery.

Comparing single-site with multisite rTMS for the treatment of chronic tinnitus - clinical effects and neuroscientific insights: study protocol for a randomized controlled trial

BACKGROUND

Several years ago, repetitive transcranial magnetic stimulation (rTMS) of the auditory cortex has been introduced as a treatment approach for chronic tinnitus. Even if this treatment is beneficial for a subgroup of patients, the overall effects are limited. This limitation may be due to the fact that the auditory cortex is only one of several brain areas involved in tinnitus. Whereas auditory areas are considered to code for tinnitus loudness, conscious perception of and attention allocation to tinnitus is supposed to be reflected by network activity involving frontal and parietal cortical areas. The aim of the present study is to influence this frontoparietal network more efficiently by perturbing the most important nodes with rTMS.

METHODS/DESIGN

This is a randomized, double-blind, parallel-group study. Patients receive rTMS treatment on 10 consecutive working days using either the multisite rTMS protocol (left dorsolateral prefrontal, 1,000 stimuli, 20 Hz; left temporoparietal, 1,000 stimuli, 1 Hz; right temporoparietal stimulation, 1,000 stimuli, 1 Hz) or a single-site protocol (unilateral stimulation of the temporoparietal cortex, 3,000 stimuli, 1 Hz). Individuals aged 18 to 70 years with chronic tinnitus ≥6-month duration and a Tinnitus Handicap Inventory score ≥38 are recruited for the study. A total of 50 patients are needed to detect a clinical relevant change of tinnitus severity (α = 0.05; 1 - β = 0.80). Primary outcome measures are the change in the Tinnitus Questionnaire score from baseline to the end of treatment as well as the number of treatment responders as defined by a reduction in the Tinnitus Questionnaire score of ≥5 points. Furthermore, changes in brain structure and activity are assessed using (functional) magnetic resonance imaging and electroencephalography in the resting state. Those measurements are also performed in 25 healthy control subjects.

DISCUSSION

This study is designed to reveal whether network stimulation is superior to single-site stimulation in the treatment of chronic tinnitus. Furthermore, the comparison between tinnitus patients and healthy controls and the longitudinal effects of both rTMS treatment protocols on brain structure and function allow inferences to be made about the neural correlates of tinnitus.

TRIAL REGISTRATION

Clinical Trials: NCT01663324.