Short and Long-Term Cognitive Effects of Subthalamic Deep Brain Stimulation in Parkinson's Disease and Identification of Relevant Factors

Impulse Control Disorders and Effort-Based Decision-Making in Parkinson's Disease Patients with Subthalamic Nucleus Deep Brain Stimulation

BACKGROUND

Impulse control disorders (ICD) are common side effects of dopaminergic treatment in Parkinson's disease (PD). Whereas some studies show a reduction in ICD after subthalamic nucleus deep brain stimulation (STN-DBS), others report worsening of ICD or impulsivity.

OBJECTIVE

The aim was to study ICD in the context of STN-DBS using an objective measure of decision-making.

METHODS

Ten PD patients performed an effort-based decision-making task alongside neuropsychiatric and cognitive evaluation before and 4 months after STN-DBS. Further, 33 PD patients underwent the same experimental procedures just once after an average 40 months of chronic STN-DBS. Participants were examined preoperatively in the medication on state and postoperatively in the medication on/stimulation ON state. Mixed linear models were used to assess the impact of ICD and STN-DBS on acceptance rate and decision time in the task while controlling for motor symptom burden, cognitive measures, and dopaminergic medication.

RESULTS

Results revealed an increased willingness to exert high levels of effort in return for reward in patients with ICD, but acceptance rate was not modulated by chronic STN-DBS. Further, ICD, cognitive processing speed, and STN-DBS were all identified as positive predictors for faster decision speed. ICD scores showed a tendency to improve 4 months after STN-DBS, without an increase in apathy scores.

CONCLUSIONS

Chronic STN-DBS and ICD facilitate effort-based decision-making by speeding up judgment. Furthermore, ICD enhances the willingness to exert high levels of effort for reward. Both STN-DBS and dopaminergic medication impact motivated behavior and should be titrated carefully to balance neuropsychiatric symptoms.

Preoperative cognitive profile predictive of cognitive decline after subthalamic deep brain stimulation in Parkinson's disease

Cognitive decline represents a severe non-motor symptom of Parkinson's disease (PD) that can significantly reduce the benefits of subthalamic deep brain stimulation (STN DBS). Here, we aimed to describe post-surgery cognitive decline and identify pre-surgery cognitive profile associated with faster decline in STN DBS-treated PD patients. A retrospective observational study of 126 PD patients treated by STN DBS combined with oral dopaminergic therapy followed for 3.54 years on average (SD = 2.32) with repeated assessments of cognition was conducted. Pre-surgery cognitive profile was obtained via a comprehensive neuropsychological examination and data analysed using exploratory factor analysis and Bayesian generalized linear mixed models. On the whole, we observed a mild annual cognitive decline of 0.90 points from a total of 144 points in the Mattis Dementia Rating Scale (95% posterior probability interval [-1.19, -0.62]) with high inter-individual variability. However, true score changes did not reach previously reported reliable change cut-offs. Executive deficit was the only pre-surgery cognitive variable to reliably predict the rate of post-surgery cognitive decline. On the other hand, exploratory analysis of electrode localization did not yield any statistically clear results. Overall, our data and models imply mild gradual average annual post-surgery cognitive decline with high inter-individual variability in STN DBS-treated PD patients. Nonetheless, patients with worse long-term cognitive prognosis can be reliably identified via pre-surgery examination of executive functions. To further increase the utility of our results, we demonstrate how our models can help with disentangling true score changes from measurement error in future studies of post-surgery cognitive changes.

The human subthalamic nucleus transiently inhibits active attentional processes

The subthalamic nucleus (STN) of the basal ganglia is key to the inhibitory control of movement. Consequently, it is a primary target for the neurosurgical treatment of movement disorders like Parkinson's disease, where modulating the STN via deep brain stimulation (DBS) can release excess inhibition of thalamocortical motor circuits. However, the STN is also anatomically connected to other thalamocortical circuits, including those underlying cognitive processes like attention. Notably, STN-DBS can also affect these processes. This suggests that the STN may also contribute to the inhibition of non-motor activity and that STN-DBS may cause changes to this inhibition. Here we tested this hypothesis in humans. We used a novel, wireless outpatient method to record intracranial local field potentials (LFP) from STN DBS implants during a visual attention task (Experiment 1, n = 12). These outpatient measurements allowed the simultaneous recording of high-density EEG, which we used to derive the steady state visual evoked potential (SSVEP), a well established neural index of visual attentional engagement. By relating STN activity to this neural marker of attention (instead of overt behaviour), we avoided possible confounds resulting from STN's motor role. We aimed to test whether the STN contributes to the momentary inhibition of the SSVEP caused by unexpected, distracting sounds. Furthermore, we causally tested this association in a second experiment, where we modulated STN via DBS across two sessions of the task, spaced at least 1 week apart (n = 21, no sample overlap with Experiment 1). The LFP recordings in Experiment 1 showed that reductions of the SSVEP after distracting sounds were preceded by sound-related γ-frequency (>60 Hz) activity in the STN. Trial-to-trial modelling further showed that this STN activity statistically mediated the sounds' suppressive effect on the SSVEP. In Experiment 2, modulating STN activity via DBS significantly reduced these sound-related SSVEP reductions. This provides causal evidence for the role of the STN in the surprise-related inhibition of attention. These findings suggest that the human STN contributes to the inhibition of attention, a non-motor process. This supports a domain-general view of the inhibitory role of the STN. Furthermore, these findings also suggest a potential mechanism underlying some of the known cognitive side effects of STN-DBS treatment, especially on attentional processes. Finally, our newly established outpatient LFP recording technique facilitates the testing of the role of subcortical nuclei in complex cognitive tasks, alongside recordings from the rest of the brain, and in much shorter time than peri-surgical recordings.

Individual Structural Covariance Network Predicts Long-Term Motor Improvement in Parkinson Disease with Subthalamic Nucleus Deep Brain Stimulation

BACKGROUND AND PURPOSE

The efficacy of long-term chronic subthalamic nucleus deep brain stimulation (STN-DBS) in treating Parkinson disease (PD) exhibits substantial variability among individuals. The preoperative identification of suitable deep brain stimulation (DBS) candidates through predictive means becomes crucial. Our study aims to investigate the predictive value of characterizing individualized structural covariance networks for long-term efficacy of DBS, offering patients a precise and cost-effective preoperative screening tool.

MATERIALS AND METHODS

We included 138 patients with PD and 40 healthy controls. We developed individualized structural covariance networks from T1-weighted images utilizing network template perturbation, and computed the networks' topological characteristics. Patients were categorized according to their long-term motor improvement following STN-DBS. Intergroup analyses were conducted on individual network edges and topological indices, alongside correlation analyses with long-term outcomes for the entire patient cohort. Finally, machine learning algorithms were employed for regression and classification to predict post-DBS motor improvement.

RESULTS

Among the patients with PD, 6 edges (left middle frontal and left caudate nucleus, right olfactory and right insula, left superior medial frontal gyrus and right insula, right middle frontal and left paracentral lobule, right middle frontal and cerebellum, left lobule VIIb of the cerebellum and the vermis of the cerebellum) exhibited significant results in intergroup comparisons and correlation analyses. Increased degree centrality and local efficiency of the cerebellum, parahippocampal gyrus, and postcentral gyrus were associated with DBS improvement. A regression model constructed from these 6 edges revealed a significant correlation between predicted and observed changes in the unified PD rating scale (R = 0.671, P < .001) and receiver operating characteristic analysis demonstrated an area under the curve of 0.802, effectively distinguishing between patients with good and moderate improvement post-DBS.

CONCLUSIONS

Our findings reveal the link between individual structural covariance network fingerprints in patients with PD and long-term motor outcome following STN-DBS. Additionally, binary and continuous cerebellum-basal ganglia-frontal structural covariance network edges have emerged as potential predictive biomarkers for DBS motor outcome.

Developments in the prediction of cognitive changes following deep brain stimulation in persons with Parkinson's disease

INTRODUCTION

Deep brain stimulation (DBS) is an effective treatment for Parkinson's disease (PD) motor symptoms that improves function and quality of life in appropriately selected patients. Because mild to moderate cognitive declines can follow DBS and impact quality of life in a minority of patients, an important consideration involves the cognitive deficit and its prediction.

AREAS COVERED

The author briefly summarizes cognitive outcomes from DBS and reviews in more detail the risks/predictors of post-DBS cognitive dysfunction by mainly focusing on work published between 2018 and 2024 and using comprehensive neuropsychological (NP) evaluations. Most publications concern bilateral subthalamic nucleus (STN) DBS. Comment is offered on challenges and potential avenues forward.

EXPERT OPINION

STN DBS is relatively safe cognitively but declines occur especially in verbal fluency and executive function/working memory. Numerous predictors and risk factors for cognitive outcomes have been identified (age and pre-operative neuropsychological status appear the most robust) but precise risk estimates cannot yet be confidently offered. Future studies should employ study center consortia, follow uniform reporting criteria (to be developed), capitalize on advances in stimulation, biomarkers, and artificial intelligence, and address DBS in diverse groups. Advances offer an avenue to investigate the amelioration of cognitive deficits in PD using neuromodulation.

Bidirectional Interplay between Deep Brain Stimulation and Cognition in Parkinson's Disease: A Systematic Review

BACKGROUND

Deep brain stimulation (DBS) is efficacious for treating motor symptoms in Parkinson's disease (PD).

OBJECTIVES

The aim is to evaluate the evidence regarding DBS effectiveness after postoperative cognitive deterioration, the impact of preoperative cognition on DBS effectiveness, and the impact of DBS on cognition.

METHODS

Literature searches were performed on MEDLINE, EMBASE, and CENTRAL (Cochrane library). Primary outcomes were OFF-drug Unified Parkinson Disease Rating Scale Part III score and cognitive test scores.

RESULTS

DBS effectiveness did not differ in patients with postoperative declining compared to stable cognition (n = 5 studies). Preoperative cognition did not influence DBS effectiveness (n = 1 study). DBS moderately decreased verbal fluency compared to the best medical treatment (n = 24 studies), which may be transient.

CONCLUSION

DBS motor effectiveness in PD does not appear to be influenced by cognition. DBS in PD seems cognitively safe, except for a moderate decline in verbal fluency. Further research is warranted. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Relationship between serum uric acid levels and the outcome of STN-DBS in Parkinson's disease

BACKGROUND

Uric acid is a natural antioxidant and it has been shown that low levels of uric acid may be a risk factor for the development of Parkinson's disease. We aimed to investigate the relationship between uric acid and improvement of motor symptoms in patients with Parkinson's disease after subthalamic nucleus deep brain stimulation.

METHODS

We analyzed the correlation between serum uric acid levels in 64 patients with Parkinson's disease and the rate of improvement of motor symptoms 2 years after subthalamic nucleus deep brain stimulation.

RESULTS

A non-linear correlation was observed between uric acid levels and the rate of motor symptom improvement after subthalamic nucleus deep brain stimulation, during both the drug-off and drug-on periods.

CONCLUSIONS

Uric acid is positively associated with the rate of motor symptom improvement in subthalamic nucleus deep brain stimulation within a certain range.