Transcranial direct current stimulation for learning and memory in Parkinson's disease: a systematic review

Cognitive impairment affecting memory and learning processes is a common non-motor feature of Parkinson's disease (PD) and contributes substantially to functional decline and a reduced quality of life. Transcranial direct current stimulation (tDCS) has emerged as a potentially beneficial non-invasive neuromodulation technique capable of modulating cortical plasticity and enhancing cognitive and motor performance. However, its specific effects on memory- and learning-related outcomes in PD remain unclear.

To systematically review and synthesize the available evidence regarding the effects of tDCS on memory and learning processes in individuals with Parkinson's disease.

A systematic review was conducted following PRISMA guidelines, with the protocol registered in PROSPERO (CRD42024559548). PubMed, Scopus, and Web of Science were searched between September and December 2025. Randomized controlled trials in individuals with PD evaluating the effects of tDCS on memory-, learning-, or cognition-related outcomes were included. Study selection, data extraction, and risk-of-bias assessment (ROB-2) were performed systematically.

Nineteen studies (2006-2024) with sample sizes of 9-42 participants were included. Most protocols used 1-2 mA stimulation targeting the dorsolateral prefrontal cortex (DLPFC) and primary motor cortex (M1). Improvements were observed in working memory, verbal fluency, executive function, and processing speed, particularly in multi-session protocols combined with cognitive or motor training. M1 stimulation was associated with enhanced motor learning consolidation, whereas single-session interventions showed limited effects. Limitations include small samples, methodological heterogeneity, and limited follow-up.

Current evidence suggests potential effects of tDCS in memory and learning processes in PD, although evidence remains limited and heterogeneous, especially when delivered in repeated sessions and combined with training targeting frontostriatal dysfunction. However, variability in protocols and study quality limits generalizability. Larger, well-controlled trials with standardized designs are needed to establish robust clinical recommendations.

https://www.crd.york.ac.uk/PROSPERO/view/CRD42024559548, identifier CRD42024559548.