Abstract
Recent evidence suggests that deep brain stimulation (DBS) of the subthalamic nucleus (STN) in Parkinson's disease (PD) mediates its clinical effects by modulating cortical oscillatory activity, presumably via a direct cortico-subthalamic connection. This observation might pave the way for novel closed-loop approaches comprising a cortical sensor. Enhanced beta oscillations (13-35 Hz) have been linked to the pathophysiology of PD and may serve as such a candidate marker to localize a cortical area reliably modulated by DBS. However, beta-oscillations are widely distributed over the cortical surface, necessitating an additional signal source for spotting the cortical area linked to the pathologically synchronized cortico-subcortical motor network. In this context, both cortico-subthalamic coherence and cortico-muscular coherence (CMC) have been studied in PD patients. Whereas, the former requires invasive recordings, the latter allows for non-invasive detection, but displays a rather distributed cortical synchronization pattern in motor tasks. This distributed cortical representation may conflict with the goal of detecting a cortical localization with robust biomarker properties which is detectable on a single subject basis. We propose that this limitation could be overcome when recording CMC at rest. We hypothesized that—unlike healthy subjects—PD would show CMC at rest owing to the enhanced beta oscillations observed in PD. By performing source space analysis of beta CMC recorded during resting-state magnetoencephalography, we provide preliminary evidence in one patient for a cortical hot spot that is modulated most strongly by subthalamic DBS. Such a spot would provide a prominent target region either for direct neuromodulation or for placing a potential sensor in closed-loop DBS approaches, a proposal that requires investigation in a larger cohort of PD patients.
Highlights
Cortico-subcortical networks of Parkinson’s disease (PD) patients are characterized by pathological circuit dynamics such as dysfunctional synchronization in the beta-frequency (12–35 Hz) band (Little and Brown, 2014)
We suggest that—unlike in healthy subjects—(I) cortico-muscular coherence (CMC) would be detectable in the PD condition even in the absence of movement due to the disease-specific enhanced beta oscillations
We performed source space analysis of beta CMC recorded during resting-state MEG and deep brain stimulation (DBS) and provide proof-of-concept evidence for a cortical hot spot that is most strongly modulated by subthalamic DBS
Summary
Cortico-subcortical networks of Parkinson’s disease (PD) patients are characterized by pathological circuit dynamics such as dysfunctional synchronization in the beta-frequency (12–35 Hz) band (Little and Brown, 2014). To provide proof-of-concept evidence, we implemented a MEG set-up for resting-state CMC and DBS to perform source space analysis of related cortical activity. Time periods immediately following DBS were compared with the 360 s of baseline measurement at rest before the stimulation trials. This approach was chosen because: (i) methods for suppressing the stimulation artifact in MEG recordings during simultaneous monopolar DBS might not be sufficiently effective for interpreting stimulation results (Devos, 2004; Silberstein et al, 2005; Airaksinen et al, 2012). During STN-DBS, the same beta-CMC (Figure 3A) and beta power (Figure 3B) source-cluster revealed the strongest stimulation-induced changes, i.e., decreases of CMC and cortical power in the beta-band
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