Use of low-frequency repetitive transcranial magnetic stimulation to reduce context-dependent learning in people with Parkinson's disease

BACKGROUND: Compared with age-matched non-disabled adults, people with Parkinson's disease (PD) demonstrated greater context-dependent learning, a phenomenon in which an individual shows inferior motor performance when the testing environmental context is different from the original practice context. Additionally, enhanced context-dependency has been shown to be associated with an increased activation of the dorsolateral prefrontal cortex (DLPFC). AIM: This study aimed to determine whether context-dependent learning in people with PD could be reduced by decreasing DLPFC activation with low frequency repetitive transcranial magnetic stimulation (rTMS). DESIGN: Quasi-experimental pre-/post-test controlled study. SETTING: University laboratory. POPULATION: Twenty-seven participants (18 individuals with PD and 9 age-matched non-disabled adults) were recruited into the PD, PD_ rTMS (PD participants who received low frequency rTMS), and Control groups. METHODS: All participants practiced a finger sequence task containing 3 sequences embedded within specific contexts (colored circles and spatial location on a computer screen) on the first day. On day 2, the participants were tested under the SWITCH and SAME conditions. In the SWITCH condition, the sequence-context association changed from that of practice; in the SAME condition, the sequence-context association remained the same as practice. The PD rTMS group received 1 Hz rTMS applied over the left DLPFC on the second day before the testing conditions. Switch cost, the performance difference between the SWITCH and SAME conditions, was calculated to indicate context-dependency. RESULTS: All participants improved throughout practice on the first day. Analysis of the switch cost revealed a significant group main effect (P=0.050). Post-hoc analysis revealed that the PD_rTMS group had significantly smaller switch cost than the PD group (P=0.031) but not the control group. CONCLUSIONS: Low frequency rTMS applied over DLPFC reduced context-dependency in people with PD. CLINICAL REHABILITATION IMPACT: The findings provide a preliminary evidence of using low frequency rTMS as an adjuvant intervention approach to facilitate individuals with PD to generalize a learned motor task from one environmental context to another.