DBS may aid cortical plasticity in Parkinson’s patients

By Eleanor McDermid, Senior medwireNews Reporter

Deep-brain stimulation of the subthalamic nucleus (STN-DBS) may help to restore long-term potentiation (LTP)-like plasticity in the motor cortex of patients with Parkinson’s disease (PD), a study shows.

The research by Robert Chen (University of Toronto, Ontario, Canada) and team found that while neither STN-DBS nor dopaminergic medication alone could significantly improve LTP-like plasticity in PD patients, the combination restored it to a level close to that observed in healthy volunteers.

“These findings suggest that dopaminergic medications together with STN-DBS are needed to restore LTP-like plasticity in motor cortex in patients with advanced PD, supporting the suggestion that STN-DBS and dopaminergic medications have synergistic effects in patients with PD”, the team writes in Neurology.

The researchers used paired associative stimulation (PAS) to induce LTP-like changes in eight patients with PD who had bilateral STN-DBS for at least 6 months.

When PD patients were off medication and off stimulation, PAS had no effect on motor-evoked potentials (MEPs) in the abductor pollicis brevis muscle on their most affected side. And PAS also had no effect when they were either on medication or on stimulation alone.

But when patients were on medication and stimulation simultaneously, their average MEP increased a significant 55.8% from baseline at 30 minutes after PAS and 57.0% at 60 minutes, which was close to the respective 67.7% and 72.3% increases observed in nine age-matched healthy controls.

“Normalization of motor cortex plasticity may be one of the mechanisms of action of STN-DBS”, say Chen et al.

However, the lack of effect of PAS in the stimulation-off states indicates that the effect of STN-DBS on cortical plasticity is not lasting, they add.

Immediately after PAS, control participants had a prolonged cortical silent period (CSP) relative to at baseline, an effect that was not observed in the patients, regardless of their medication and stimulation status. “Therefore, STN stimulation did not directly affect the inhibitory intracortical system mediating the CSP”, say the researchers.

They also note that STN-DBS reduced dyskinesias in all their patients, and speculate that the need for stimulation to restore LTP-like cortical plasticity in patients with dyskinesias, but not in those without, may point to a direct role for STN-DBS in alleviating dyskinesias.

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