Melatonin serum level, sleep functions, and depression level after bilateral anodal transcranial direct current stimulation in patients with Parkinson's disease: a feasibility study

Effect of Transcranial Direct Current Stimulation (tDCS) on Depression in Parkinson's Disease-A Narrative Review

INTRODUCTION

Depression is the most prevalent comorbid neuropsychiatric condition in individuals with Parkinson's disease (PD), and its underlying mechanisms are not yet fully understood. Current treatment methods are characterised by moderate effectiveness and possible side effects, prompting the search for new non-invasive and safe treatment methods.

METHODS

This narrative review explores the use of transcranial direct current stimulation (tDCS) in the treatment of depression in PD, based on neuropsychological measures. Searches were conducted in the PubMed/Medline, Research Gate, and Cochrane databases.

RESULTS

Nine relevant studies were identified, where depression scores served as either primary or secondary outcomes. Stimulation protocols displayed heterogeneity, especially concerning choice of stimulation site. Patient samples were also heterogeneous. The majority of the studies incorporated anodal stimulation targeting the left dorsolateral prefrontal cortex (DLPFC). The results revealed a reduction in depression scores among PD patients following tDCS. Potential mechanisms through which tDCS may alleviate depression in PD were discussed and recommendations for future research were made.

CONCLUSIONS

Preliminary evidence suggests that tDCS applied anodally to the left DLPFC reduces depression scores in people with PD; however, due to the heterogeneity of the studies analysed, the use of tDCS in this field should be approached with caution and warrants further validation and confirmation.

Non-Pharmacological Interventions for Depression and Anxiety in Parkinson's Disease

Non-pharmacological interventions, including cognitive-behavioral therapy (CBT), non-invasive brain stimulation (NIBS), electroconvulsive therapy (ECT), light therapy (LT), and physical rehabilitation/exercise, have shown promise as effective approaches to treat symptoms of depression and anxiety in individuals with Parkinson's disease (PD). In this narrative literature overview, we discuss the state-of-the-art regarding these treatment options and address future perspectives for clinical practice and research. Non-pharmacological interventions hold promise to treat depression and anxiety in PD. There is meta-analytic evidence for the efficacy of CBT, NIBS, ECT, LT, and exercise on improving depressive symptoms. For the treatment of anxiety symptoms, CBT shows large effects but scientific evidence of other non-pharmacological interventions is limited. Importantly, these treatments are safe interventions with no or mild side-effects. More research is needed to tailor treatment to the individuals' needs and combined interventions may provide synergistic effects.We conclude that non-pharmacological interventions should be considered as alternative or augmentative treatments to pharmacological and neurosurgical approaches for the treatment of depression and anxiety in individuals with PD.

Application of Transcranial Direct Current Stimulation in Sleep Disturbances

Sleep disturbances are common across all age groups, and they encompass a broad range of impairments of daytime functioning and comorbid various clinical conditions. However, current treatment methods for sleep disturbances have several limitations. As the ‘top-down’ pathway is known to play an important role in sleep-wake regulation, and as neuronal activity abnormalities have been reported as a potential pathological mechanism of sleep disturbances, the use of non-invasive brain stimulation—such as transcranial direct current stimulation (tDCS) in treating sleep disturbances—has emerged. In the present review, we first explain the mechanism of tDCS, and we also introduce recent studies that have applied tDCS to sleep disorders, along with other sleep-related tDCS studies. In conclusion, many studies have achieved improvements in sleep state, although some of these studies have reported inconsistent effects of tDCS according to the protocol and the conditions used. Further studies are needed to explore the optimal protocols to use when applying tDCS in each sleep disturbance and to enhance the evidence on the clinical efficacy of tDCS.

Transcranial direct current stimulation in the treatment of anxiety and depression in patients with oral cancer during perioperative period

This study retrospectively investigated the efficacy of transcranial direct current stimulation (tDCS) in the treatment of anxiety and depression in patients with oral cancer (OC) during the perioperative period (PPP). This retrospective study reviewed the electronic medical records of patients who underwent OC surgery and experienced anxiety and depression during PPP. The patients were divided into the treatment (n = 36) and control (n = 36) groups. The patients in the treatment group received tDCS, whereas those in the control group did not receive tDCS. The primary outcomes included the Self-rating Anxiety Scale (SAS) and the Self-rating Depression Scale (SDS). Secondary outcomes included adverse events (AEs). We analyzed the outcome data before and after treatment. After treatment, patients in the treatment group achieved greater relief in SAS (P < .01) and SDS (P < .01) scores than those in the control group. Regarding safety, no electronic medical records reported any AEs in this study. The results of this study showed that tDCS may help relieve depression and anxiety in patients with OC during PPP. However, high-quality prospective randomized controlled trials are required to confirm these findings.

Non-Invasive Brain Stimulation Effects on Biomarkers of Tryptophan Metabolism: A Scoping Review and Meta-Analysis

Abnormal activation of the kynurenine and serotonin pathways of tryptophan metabolism is linked to a host of neuropsychiatric disorders. Concurrently, noninvasive brain stimulation (NIBS) techniques demonstrate high therapeutic efficacy across neuropsychiatric disorders, with indications for modulated neuroplasticity underlying such effects. We therefore conducted a scoping review with meta-analysis of eligible studies, conforming with the PRISMA statement, by searching the PubMed and Web of Science databases for clinical and preclinical studies that report the effects of NIBS on biomarkers of tryptophan metabolism. NIBS techniques reviewed were electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS), and transcranial direct current stimulation (tDCS). Of the 564 search results, 65 studies were included with publications dating back to 1971 until 2022. The Robust Bayesian Meta-Analysis on clinical studies and qualitative analysis identified general null effects by NIBS on biomarkers of tryptophan metabolism, but moderate evidence for TMS effects on elevating serum serotonin levels. We cannot interpret this as evidence for or against the effects of NIBS on these biomarkers, as there exists several confounding methodological differences in this literature. Future controlled studies are needed to elucidate the effects of NIBS on biomarkers of tryptophan metabolism, an under-investigated question with substantial implications to clinical research and practice.