Introduction: Beta oscillations play an important role in gating movement. Because pathological oscillatory changes in the beta band represent a hallmark of Parkinson’s disease (PD), tracking oscillatory changes in this band has been proposed as a marker for closed loop stimulation. However, the dynamics of casual influences across the motor circuit during movement remain unknown. Using intracranial local field potential (LFP) recordings, we employed both standard functional connectivity and Event-Related Causality (ERC) techniques to explore these interactions.
Methods: LFPs were recorded simultaneously from subthalamic nucleus (STN) and sensorimotor cortex while PD subjects (n=8) undergoing the implantation of DBS leads performed an incentivized, bimanual handgrip task. Using the beta frequency band between 13-30 Hz, functional connectivity was estimated using wavelet-based phase locking values (PLV), and ERC was calculated by constructing a multivariate autoregressive model based on the signal of interest from M1, S1 and STN channels. A false discovery rate correction of 5% was applied.
Results: All the patients showed significant causal interactions between STN and sensorimotor cortex that coincided with movement epochs showing significant PLV on the individual level. In the 200 ms prior to movement, precentral beta activity modulated beta activity in the STN, implying that cortical beta activity drives the STN beta activity in that epoch. Reciprocal modulations between the cortex and STN were apparent at the termination of movement. Causal influences from the precentral cortex to the STN in the beta band around 0.5ms after movement onset correlated significantly with the time to peak force (rho=0.86, corrected p<0.0028).
Conclusions: The directionality of causal interactions across the basal ganglia-cortical motor loop are specific to The directionality of causal interactions across the basal ganglia-cortical motor loop are specific to different phases of motor planning and execution. These novel data highlight the value of intraoperative recordings for furthering our understanding of cortical-basal ganglia models.
Patient Care: The development of adaptive, or closed-loop, deep-brain stimulation will require a signal of interest to optimize the parameters of stimulation. One candidate is movement-related modulation of beta oscillations. Understanding how this oscillation propagates in the motor circuit and the timing of signals carrying movement information is paramount to designing these systems.
Learning Objectives: By the end of this session, participants should be able to: 1) Describe the current understanding of connectivity across the cortico-basal ganglia circuit, 2) Describe the importance of novel techniques in acquiring and analyzing neural data on understanding the neurobiology of disease, 3) Discuss the utility of connectivity measure as biomarkers for closed loop stimulation.