Diurnal modulation of subthalamic beta oscillatory power in Parkinson's disease patients during deep brain stimulation

Background: Beta band activity in the subthalamic local field potential (LFP) is correlated with Parkinson's disease (PD) symptom severity, and is the therapeutic target and feedback signal for adaptive deep brain stimulation (aDBS). While clinically relevant beta fluctuations in PD patients are well characterised on shorter timescales and in the clinic, it is not known how beta activity evolves around the diurnal cycle, outside a clinical setting. Objective: To characterise diurnal fluctuations in beta amplitude in PD patients receiving continuous, high frequency DBS. Methods: We obtained chronic recordings (34+/-13 days) of subthalamic beta power in PD patients implanted with the Percept DBS device during high-frequency DBS, and analysed its diurnal properties. To investigate the influence of non-frequency-specific effects and artifacts, we compared beta to contralateral theta amplitude and recorded LFPs during various movements. Results: Beta power had strong 24-hour periodicity, and time of day explained 41+/-9% of the variance in all long-term beta power recordings (p<0.001 in all patients). For all patients, beta activity was high during the day and reduced at night. Beta activity was not fully explained by theta activity and could show independent diurnal modulation. Movement artifacts affected the recorded LFPs, influenced band power estimates, and could have contributed to diurnal patterns in some patients. Conclusions: Diurnal fluctuations in beta amplitude will need to be accommodated in aDBS to prevent suboptimal stimulation, particularly at night. Careful screening and/or mitigation of movement artifacts is needed to ensure that the signal is suitable for adaptive stimulation or neurophysiological investigation.