The effects of levodopa and ongoing deep brain stimulation on subthalamic beta oscillations in Parkinson's disease

Local field potentials (LFPs) recorded through electrodes implanted in the subthalamic nucleus (STN) for deep brain stimulation (DBS) in patients with Parkinson's disease (PD) show that oscillations in the beta frequency range (8–20 Hz) decrease after levodopa intake. Whether and how DBS influences the beta oscillations and whether levodopa- and DBS-induced changes interact remains unclear. We examined the combined effect of levodopa and DBS on subthalamic beta LFP oscillations, recorded in nine patients with PD under four experimental conditions: without levodopa with DBS turned off; without levodopa with DBS turned on; with levodopa with DBS turned on; and with levodopa with DBS turned off. The analysis of STN-LFP oscillations showed that whereas levodopa abolished beta STN oscillations in all the patients (p = 0.026), DBS significantly decreased the beta oscillation only in five of the nine patients studied (p = 0.043). Another difference was that whereas levodopa completely suppressed beta oscillations, DBS merely decreased them. When we combined levodopa and DBS, the levodopa-induced beta disruption prevailed and combining levodopa and DBS induced no significant additive effect (p = 0.500). Our observations suggest that levodopa and DBS both modulate LFP beta oscillations.

Research Highlights
► When patients with Parkinson's disease (PD) undergo deep brain stimulation (DBS) motor symptoms improve by almost 60%, but some fluctuations persist.
► When antiparkinsonian medication is reduced to the minimum fluctuations disappear, thus raising the question whether subthalamic nucleus (STN) DBS induces levodopa-like effects, acting synergically or whether DBS and levodopa act independently and differ in their mechanisms of action.
► Examining the combined effect of levodopa and DBS on subthalamic beta (8–20 Hz) oscillations, our results showed that whereas levodopa abolished beta STN oscillations in all the patients, DBS decreased significantly the beta oscillation only in some patients.
► When levodopa and DBS were combined, the levodopa-induced beta disruption prevailed, and combining levodopa and DBS induced no significant additive effect.
► Our observations suggest that levodopa and DBS both modulate LFP beta oscillations.