Background: Freezing of gait (FOG) is among the most common and disabling symptoms of Parkinson’s disease (PD). Studies show that deep brain stimulation (DBS) of the subthalamic nucleus (STN) can reduce FOG severity. However, there is uncertainty about pathways that need to be modulated to improve FOG. Objective: To investigate whether STN-DBS effectively reduces FOG postoperatively and whether structural connectivity of the stimulated tissue explains variance of outcomes. Methods: We investigated 47 patients with PD and preoperative FOG. Freezing prevalence and severity was primarily assessed using the Freezing of Gait Questionnaire (FOG-Q). In a subset of 18 patients, provoked FOG during a standardized walking course was assessed. Using a publicly available model of basal-ganglia pathways we determined stimulation-dependent connectivity associated with postoperative changes in FOG. A region-of-interest analysis to a priori defined mesencephalic regions was performed using a disease-specific normative connectome. Results: Freezing of gait significantly improved six months postoperatively, marked by reduced frequency and duration of freezing episodes. Optimal stimulation volumes for improving FOG structurally connected to motor areas, the prefrontal cortex and to the globus pallidus. Stimulation of the lenticular fasciculus was associated with worsening of FOG. This connectivity profile was robust in a leave-one-out cross-validation. Subcortically, stimulation of fibers crossing the pedunculopontine nucleus and the substantia nigra correlated with postoperative improvement. Conclusion: STN-DBS can alleviate FOG severity by modulating specific pathways structurally connected to prefrontal and motor cortices. More differentiated FOG assessments may allow to differentiate pathways for specific FOG subtypes in the future.

Intra- and perioperatively recorded local field potential (LFP) activity of the nucleus subthalamicus (STN) has been suggested to guide contact selection in patients undergoing deep brain stimulation (DBS) for Parkinson’s disease (PD). Despite the invention of sensing capacities in chronically implanted devices, a comprehensible algorithm that enables contact selection using such recordings is still lacking. We evaluated a fully automated algorithm that uses the weighted average of bipolar recordings to determine effective monopolar contacts based on elevated activity in the beta band. LFPs from 14 hemispheres in seven PD patients with newly implanted directional DBS leads of the STN were recorded. First, the algorithm determined the stimulation level with the highest beta activity. Based on the prior determined level, the directional contact with the highest beta activity was chosen in the second step. The mean clinical efficacy of the contacts chosen using the algorithm did not statistically differ from the mean clinical efficacy of standard contact selection as performed in clinical routine. All recording sites were projected into MNI standard space to investigate the feasibility of the algorithm with respect to the anatomical boundaries of the STN. We conclude that the proposed algorithm is a first step towards LFP-based contact selection in STN-DBS for PD using chronically implanted devices.

Gait impairments such as freezing of gait (FOG) are among the most common and disabling symptoms of Parkinson's disease (PD). While the efficacy of deep brain stimulation (DBS) of the subthalamic nucleus (STN) in patients with early or advanced PD has been proven in large randomised controlled trials, its effect on gait impairments is still insufficiently understood. Moreover, there is uncertainty about pathways that need to be modulated to improve gait impairments. In this bi-centric study, we investigated how STN-DBS alters FOG in 47 subjects with PD. We assessed freezing prevalence and severity using the Freezing of Gait Questionnaire and Item 14 of the Unified Parkinson's Disease Rating Scale-II. Using a model of publicly available basal-ganglia pathways we determined a connectivity profile for postoperative changes in FOG. Compared to preoperative baseline, freezing of gait significantly improved six months postoperatively, marked by reduced frequency and duration of freezing episodes. We found that optimal stimulation sites for improving freezing of gait structurally connected to primary and supplementary motor areas, the dorsolateral prefrontal cortex and to the globus pallidus. Stimulation of the lenticular fasciculus was associated with worsening of freezing of gait. Our findings highlight the need for optimal identification and characterisation for network structures that can be implemented in stereotactic planning and can additionally pose a target for postoperative stimulation strategies.

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ObjectiveThis study aims to shed light on structural networks associated with stimulation-induced dysarthria (SID) and to derive a data-driven model to predict SID in patients with Parkinson’s Disease (PD) and deep brain stimulation (DBS) of the subthalamic nucleus (STN).MethodsRandomized, double-blinded monopolar reviews determining SID thresholds were conducted in 25 patients with PD and STN-DBS. A fiber-based mapping approach, based on the calculation of fiber-wise Odds Ratios for SID, was employed to identify the distributional pattern of SID in the STN’s vicinity. The ability of the data-driven model to classify stimulation volumes as “causing SID” or “not causing SID” was validated by calculating receiver operating characteristics (ROC) in an independent out-of-sample cohort comprising 14 patients with PD and STN-DBS.ResultsLocal fiber-based stimulation maps showed an involvement of fibers running lateral and postero-medial to the STN in the pathogenesis of SID, independent of the investigated hemisphere. ROC-analysis in the independent out-of-sample cohort resulted in a good fit of the data-driven model for both hemispheres (AUCleft= 0.88, AUCright= 0.88).InterpretationThis study reveals an involvement of both, cerebello-thalamic fibers, as well as the pyramidal tract, in the pathogenesis of SID in STN-DBS. The results may impact future postoperative programming strategies to avoid SID in patients with PD and STN-DBS.

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Background: Deep brain stimulation (DBS) of the medial thalamus is an evolving therapy for severe, treatment-refractory Tourette syndrome (TS). It remains unanswered which functionally connected networks need to be modulated to obtain optimal treatment results. Methods: We assessed treatment response of 15 patients with TS untergoing thalamic DBS six and twelve months postoperatively using the Yale Global Tic Severity Scale (YGTSS) tic score. For each time point, functional connectivity maps seeding from stimulation sites were calculated based on a normative functional connectome derived from 1000 healthy subjects. Resulting maps were analyzed in a voxel-wise mixed model for repeated measurements to identify patterns of connectivity associated with tic reduction. Results: Connectivity of stimulation to the medial frontal cortex, bilateral insulae and sensorimotor cortex was associated with tic reduction. Connectivity with the temporal lobe, cerebellum, ventral striatum and orbitofrontal cortex was negatively associated. The overall connectivity pattern was robust to leave-one-out cross-validation, explaining 25 % of outcome variance (R = 0.500; p = 0.005). Conclusions: We delineated a functional connectivity profile seeding from stimulation sites associated with TS-DBS outcome. This pattern comprised areas linked to the processing of premonitory urges and tic execution, thereby extending our current understanding of effective neuromodulation for TS.

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