Objective: This study aims to investigate the effects of cerebellar theta burst stimulation (TBS) on working memory (WM) performance in patients with Parkinson’s disease (PD) and healthy controls.

Background: Research suggests that the cerebellum is involved in working memory (WM). Many patients with PD experience WM impairment. Previous research reported changes in the cerebellar connectivity with the prefrontal cortex (PFC) in PD. The contribution of the cerebellum to WM is thought to be achieved through its connections with the PFC. Previous studies showed that TBS, a form of repetitive transcranial magnetic stimulation (rTMS), on the cerebellum changes its functional connectivity with the PFC in neurologically healthy controls. Specifically, excitatory intermittent TBS (iTBS) increases, whereas inhibitory continuous TBS (cTBS) decreases this functional connectivity. No studies examined the effects of cerebellar TBS on WM in PD. We hypothesized that iTBS on the cerebellum will improve WM, whereas cTBS will disrupt it in patients with PD and healthy controls.

Method: Eight patients with idiopathic PD (3 women) and 16 age-matched healthy controls (10 women) participated in this study. Bilateral cerebellar stimulation was applied with a figure-of-eight coil at 3 cm lateral and 1 cm below the inion. The participants received iTBS, cTBS, and sham iTBS in three separate sessions in random order. Within 30 minutes after TBS, the participants performed three WM tasks: letter 2-back, digit span forward (DSF), and digit span backward (DSB). For the 2-back task, we calculated the discriminability index (d-prime). The score ranges were 0-16 points for DSF and 0-14 points for DSB.

Results: The mixed design repeated measures ANOVA revealed a significant effect of the type of stimulation (iTBS/cTBS/Sham) on performance in the DSB task (F(2, 44) = 5.997; p = 0.005; η_p² = 0.214). We performed a planned comparison (a priori contrast), and it showed that scores in the cTBS condition were significantly lower than in the sham condition (t(44) = 3.455; p = 0.001). iTBS and cTBS did not affect performance in the 2-back and DSF tasks compared to sham. No significant differences were found between patients and controls in any of the tasks.

Conclusion: The findings support the hypothesis that the cerebellum is involved in working memory, and this contribution may be disrupted by cTBS in patients with PD and healthy controls.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/effects-of-cerebellar-theta-burst-stimulation-on-working-memory-in-parkinsons-disease/