Impact of prefrontal intermittent theta-burst stimulation on working memory and executive function in Parkinson's disease: a double-blind sham-controlled pilot study

Cognitive impairment is a prevalent non-motor feature of Parkinson's disease (PD) which can present even in early stages of the disease. Impairments in executive processing and working memory (WM) are common and have been attributed, in part, to abnormalities within the dorsolateral prefrontal cortex (DLPFC) and broader fronto-striatal circuitry. Previous studies in cognitively normal adults have suggested intermittent Theta Burst Stimulation (iTBS), an excitatory plasticity-inducing non-invasive brain stimulation technique, can enhance these cognitive functions. Fourteen participants with a diagnosis of idiopathic PD received either Active or Sham iTBS over the left DLPFC across two separate experimental sessions as part of a double-blind sham-controlled crossover experimental design. The Berg's Card Sorting Test (BCST) and N-Back tasks, which measure executive function and WM respectively, were administered prior to iTBS and again five- and 30-minutes following stimulation. Despite being well-tolerated, iTBS failed to modulate performance on any of the cognitive outcome measures. This finding was further supported by Bayes Factor analyses which indicated moderate levels of support for the null hypothesis overall. This initial pilot study therefore does not support single-session iTBS as an efficacious method for modulating either executive processes or WM in PD. We discuss potential reasons for this finding along with directions for future research.