Effect of left temporoparietal transcranial direct current stimulation on self-bias effect and retrospective intentional binding paradigm: A randomised, double-blind, controlled study.

BACKGROUND: Self-bias effect is expressed as a preferential selection and accelerated perception of self-related sensory information. Intentional binding (IB) is a related phenomenon where the sensory outcome from a voluntary action and the voluntary action itself are perceived to be closer to each other in time in both predictive (voluntary action predicting sensory consequence) and retrospective (sensory consequence features triggering self-related inference) contexts. Recent evidence indicates that self-related visual stimuli can affect retrospective intentional binding (rIB). We aimed to 1) replicate rIB in the auditory context, and 2) investigate the potential role of left temporoparietal junction (l-TPJ), a crucial node for the self-monitoring process, in self-bias effect and intentional binding effect by manipulating l-TPJ activity with neuromodulation [using High-Definition Transcranial Direct Current Stimulation (HD-tDCS)]. We anticipated self-bias and rIB effects to increase with anodal stimulation of l-TPJ in comparison to cathodal-stimulation of l-TPJ. METHODS: Fourteen, right-handed, healthy participants performed sound-label matching (matching tones to self-and-other labels) and rIB (estimating time interval between a button press and a self/other labelled tone) tasks. Each participant underwent both anodal and cathodal stimulation of l-TPJ in separate sessions (at least 72 h apart). Assignment of HD-tDCS type was random and counter-balanced across participants. Behavioural data was collected at three time points: once at baseline (no-stimulation), and twice after stimulation with HD-tDCS. RESULTS: Strong self-bias effect was observed across all experimental conditions. Neuromodulation of l-TPJ affected processing of other-labelled tone in the sound-label matching task. rIB was noted in baseline and anodal-HD-tDCS conditions where participants exhibited stronger binding for self-associated stimuli compared to other-associated stimuli. CONCLUSION: l-TPJ may potentially play a critical role in self-other distinction. This may have possible implications for disorders of self-disturbances like psychosis.

Effect of transcranial direct current stimulation on in-vivo assessed neuro-metabolites through magnetic resonance spectroscopy: a systematic review.

OBJECTIVES: Previous studies have examined the effect of transcranial direct current stimulation (tDCS) on the in-vivo concentrations of neuro-metabolites assessed through magnetic resonance spectroscopy (MRS) in neurological and psychiatry disorders. This review aims to systematically evaluate the data on the effect of tDCS on MRS findings and thereby attempt to understand the potential mechanism of tDCS on neuro-metabolites. METHODS: The relevant literature was obtained through PubMed and cross-reference (search till June 2020). Thirty-four studies were reviewed, of which 22 reported results from healthy controls and 12 were from patients with neurological and psychiatric disorders. RESULTS: The evidence converges to highlight that tDCS modulates the neuro-metabolite levels at the site of stimulation, which, in turn, translates into alterations in the behavioural outcome. It also shows that the baseline level of these neuro-metabolites can, to a certain extent, predict the outcome after tDCS. However, even though tDCS has shown promising effects in alleviating symptoms of various psychiatric disorders, there are limited studies that have reported the effect of tDCS on neuro-metabolite levels. CONCLUSIONS: There is a compelling need for more systematic studies examining patients with psychiatric/neurological disorders with larger samples and harmonised tDCS protocols. More studies will potentially help us to understand the tDCS mechanism of action pertinent to neuro-metabolite levels modulation. Further, studies should be conducted in psychiatric patients to understand the neurological changes in this population and potentially unravel the neuro-metabolite × tDCS interaction effect that can be translated into individualised treatment.

Transcranial direct current stimulation for treatment-resistant obsessive-compulsive disorder-A large case series.

OBJECTIVE: The present study is a large case series evaluating the benefits of transcranial direct current stimulation (tDCS) in treatment-resistant obsessive compulsive disorder (OCD). METHODS: We reviewed the charts of 32 patients with treatment-resistant OCD who received 10-20 sessions of anodal pre-SMA tDCS. RESULTS: Overall, 9 (28 %) showed at least partial response to tDCS at the end of 10-20 sessions [responders = 8 (25 %), partial responders = 1 (3%)]. Two out of three partial responders at the end of 10 sessions had response at the end of 20 sessions. CONCLUSIONS: tDCS may benefit a proportion of patients with treatment-resistant OCD.

Target specific effects of direct current stimulation in schizo-obsessive disorder: A case report.

Transcranial direct current stimulation (tDCS) is a type of non-invasive brain stimulation technique that is explored as an add-on treatment for the alleviation of symptoms across the diverse symptom domains in neuropsychiatric disorders. In psychiatry, data is emerging on the effects of tDCS as an add-on treatment in schizophrenia as well as obsessive-compulsive disorder (OCD). But despite high prevalence, the effectiveness of tDCS in co-morbid schizophrenia and OCD is lacking. This case report for the first time examines the clinical utility with target-specific effects of the add-on tDCS in a patient diagnosed with schizo-obsessive disorder.

Add-on HD-tDCS for obsessive-compulsive disorder with comorbid bipolar affective disorder: A case series.

Obsessive-compulsive disorder (OCD) with comorbid bipolar affective disorder (BPAD) is often faced with a therapeutic challenge. Pharmacological treatment strategy engaged towards alleviating symptoms in OCD has the propensity to precipitate a manic switch in patients with comorbid BPAD. Advanced non-invasive brain stimulation techniques like high definition transcranial direct current stimulation (HD-tDCS) may target the symptoms of OCD while preventing a probable manic switch in a vulnerable population. In this case series, we targeted OC symptoms in three patients by giving 2 mA of anodal HD-tDCS at their pre-SMA (localized using 10/10 EEG system) with 4 surrounding return electrodes of opposite polarity for 20 min of two sessions having an intersession gap of 20 min receiving a maximum of 20 sessions. We found that the patients showed significant improvement (more than 25%) in their OC symptoms while having no affective side effects and this effect was replicated in one of the two patients in repeating the treatment for relapse. This case series highlights the efficacy and durability of the effect of HD-tDCS as an add-on treatment modality in three patients who were treated for OC symptoms in the context of a comorbid bipolar disorder, two of them receiving repeat courses on relapse.