The persistent effects of unilateral pallidal and subthalamic deep brain stimulation on force control in advanced Parkinson's patients

Successful asymmetrical deep brain stimulation using right subthalamic and left pallidal electrodes in a patient with Parkinson's disease

PURPOSE

Despite the best efforts of neurologists, the results of pharmacotherapy in the late stages of Parkinson's disease are often disappointing and accompanied by debilitating side effects. Under these circumstances, deep brain stimulation is a viable treatment option. The aim of the meticulous pre-surgical planning is not only precise electrode implantation, but also the avoidance of intraoperative vascular conflicts potentially causing intracerebral bleeding.

MATERIAL AND METHODS

In this report, we present a patient with early-onset Parkinson's disease whose cerebral vascular anatomy precluded standard bilateral subthalamic nucleus electrode implantation. Initially, right subthalamic stimulation alone provided a very mild clinical benefit that was not reflected in the patient's quality of life. In this patient, an unusual configuration of intracerebral electrodes with right subthalamic and left pallidal stimulation electrodes was applied 15 months after the initial subthalamic electrode implantation.

RESULTS

The procedure has had a highly beneficial long-term effect without any significant complications. The greatest improvement was noted using the setting 1.8 V, 130 Hz, 90 μs at the right side (STN) and 3.7 V, 130 Hz, 120 μs at the left side (GPi). This allowed the patient to return to his daily life activities.

CONCLUSIONS

The reported case provides a new perspective of treatment possibilities in complex functional neurosurgical cases requiring exceptional individualisation of the treatment approach.

Upper extremity asymmetry due to nerve injuries or central neurologic conditions: a scoping review

BACKGROUND

Peripheral nerve injuries and central neurologic conditions can result in extensive disabilities. In cases with unilateral impairment, assessing the asymmetry between the upper extremity has been used to assess outcomes of treatment and severity of injury. A wide variety of validated and novel tests and sensors have been utilized to determine the upper extremity asymmetry. The purpose of this article is to review the literature and define the current state of the art for describing upper extremity asymmetry in patients with peripheral nerve injuries or central neurologic conditions.

METHOD

An electronic literature search of PubMed, Scopus, Web of Science, OVID was performed for publications between 2000 to 2022. Eligibility criteria were subjects with neurological conditions/injuries who were analyzed for dissimilarities in use between the upper extremities. Data related to study population, target condition/injury, types of tests performed, sensors used, real-world data collection, outcome measures of interest, and results of the study were extracted. Sackett's Level of Evidence was used to judge the quality of the articles.

RESULTS

Of the 7281 unique articles, 112 articles met the inclusion criteria for the review. Eight target conditions/injuries were identified (Brachial Plexus Injury, Cerebral Palsy, Multiple Sclerosis, Parkinson's Disease, Peripheral Nerve Injury, Spinal Cord Injury, Schizophrenia, and stroke). The tests performed were classified into thirteen categories based on the nature of the test and data collected. The general results related to upper extremity asymmetry were listed for all the reviewed articles. Stroke was the most studied condition, followed by cerebral palsy, with kinematics and strength measurement tests being the most frequently used tests. Studies with a level of evidence level II and III increased between 2000 and 2021. The use of real-world evidence-based data, and objective data collection tests also increased in the same period.

CONCLUSION

Adequately powered randomized controlled trials should be used to study upper extremity asymmetry. Neurological conditions other than stroke should be studied further. Upper extremity asymmetry should be measured using objective outcome measures like motion tracking and activity monitoring in the patient's daily living environment.

Long-Term Follow-Up of Unilateral Deep Brain Stimulation Targeting the Caudal Zona Incerta in 13 Patients with Parkinsonian Tremor

INTRODUCTION

Deep brain stimulation (DBS) is an established treatment for Parkinson's disease (PD) and other movement disorders. The ventral intermediate nucleus of the thalamus is considered as the target of choice for tremor disorders, including tremor-dominant PD not suitable for DBS in the subthalamic nucleus (STN). In the last decade, several studies have shown promising results on tremor from DBS in the posterior subthalamic area (PSA), including the caudal zona incerta (cZi) located posteromedial to the STN. The aim of this study was to evaluate the long-term effect of unilateral cZi/PSA-DBS in patients with tremor-dominant PD.

METHODS

Thirteen patients with PD with medically refractory tremor were included. The patients were evaluated using the motor part of the Unified Parkinson Disease Rating Scale (UPDRS) off/on medication before surgery and off/on medication and stimulation 1-2 years (short-term) after surgery and at a minimum of 3 years after surgery (long-term).

RESULTS

At short-term follow-up, DBS improved contralateral tremor by 88% in the off-medication state. This improvement persisted after a mean of 62 months. Contralateral bradykinesia was improved by 40% at short-term and 20% at long-term follow-up, and the total UPDRS-III by 33% at short-term and by 22% at long-term follow-up with stimulation alone.

CONCLUSIONS

Unilateral cZi/PSA-DBS seems to remain an effective treatment for patients with severe Parkinsonian tremor several years after surgery. There was also a modest improvement on bradykinesia.

Bradykinesia and Its Progression Are Related to Interhemispheric Beta Coherence

OBJECTIVE

Bradykinesia is the major cardinal motor sign of Parkinson disease (PD), but its neural underpinnings are unclear. The goal of this study was to examine whether changes in bradykinesia following long-term subthalamic nucleus (STN) deep brain stimulation (DBS) are linked to local STN beta (13-30 Hz) dynamics or a wider bilateral network dysfunction.

METHODS

Twenty-one individuals with PD implanted with sensing neurostimulators (Activa® PC + S, Medtronic, PLC) in the STN participated in a longitudinal 'washout' therapy study every three to 6 months for an average of 3 years. At each visit, participants were withdrawn from medication (12/24/48 hours) and had DBS turned off (>60 minutes) before completing a repetitive wrist-flexion extension task, a validated quantitative assessment of bradykinesia, while local field potentials were recorded. Local STN beta dynamics were investigated via beta power and burst duration, while interhemispheric beta synchrony was assessed with STN-STN beta coherence.

RESULTS

Higher interhemispheric STN beta coherence, but not contralateral beta power or burst duration, was significantly associated with worse bradykinesia. Bradykinesia worsened off therapy over time. Interhemispheric STN-STN beta coherence also increased over time, whereas beta power and burst duration remained stable. The observed change in bradykinesia was related to the change in interhemispheric beta coherence, with greater increases in synchrony associated with further worsening of bradykinesia.

INTERPRETATION

Together, these findings implicate interhemispheric beta synchrony as a neural correlate of the progression of bradykinesia following chronic STN DBS. This could imply the existence of a pathological bilateral network contributing to bradykinesia in PD. ANN NEUROL 2023;93:1029-1039.

The Intraoperative Microlesion Effect Positively Correlates With the Short-Term Clinical Effect of Deep Brain Stimulation in Parkinson's Disease

OBJECTIVE

During the surgical procedure of deep brain stimulation (DBS), insertion of an electrode in the subthalamic nucleus (STN) frequently causes a temporary improvement of motor symptoms, known as the microlesion effect (MLE). The objective of this study was to determine the correlation between the intraoperative MLE and the clinical effect of DBS.

MATERIALS AND METHODS

Thirty Parkinson's disease (PD) patients with Movement Disorder Society (MDS) Unified Parkinson's Disease Rating Scale (UPDRS) part III (MDS-UPDRS III) scores during bilateral STN-DBS implantation were included in this retrospective study. MDS-UPDRS III subscores (resting tremor, rigidity, and bradykinesia) of the contralateral upper extremity were used. During surgery, these subscores were assessed directly before and after insertion of the electrode. Also, these subscores were determined in the outpatient clinic after 11 weeks on average (on-stimulation). All assessments were performed in an off-medication state (at least 12 hours of medication washout).

RESULTS

Postinsertion MDS-UPDRS motor scores decreased significantly compared to preinsertion scores (p < 0.001 for both hemispheres). The MLE showed a positive correlation with the clinical effect of DBS in both hemispheres (rho = 0.68 for the primarily treated hemisphere, p < 0.001, and rho = 0.59 for the secondarily treated hemisphere, p < 0.01).

CONCLUSION

The MLE has a clinically relevant correlation with the effect of DBS in PD patients. These results suggest that the MLE can be relied upon as evidence of a clinically effective DBS electrode placement.

Long-term Parkinson's disease quality of life after staged DBS: STN vs GPi and first vs second lead

Deep brain stimulation (DBS) for Parkinson's disease (PD) improves quality of life (QoL), but longitudinal follow-up data are scarce. We sought to quantify long-term benefits of subthalamic nucleus (STN) vs globus pallidus internus (GPi), and unilateral vs staged bilateral PD-DBS on postoperative QoL. This is a retrospective, longitudinal, non-randomized study using the PD QoL questionnaire (PDQ)-39 in patients with STN- or GPi-DBS, and with unilateral (N = 191) or staged bilateral (an additional contralateral lead implant) surgery (N = 127 and 156 for the first and second lead, respectively). Changes in PDQ-39 summary index (PDQ-39SI) and subscores throughout 60 months of follow-up were used as the primary analysis. We applied mixed models that included levodopa and covariates that differed at baseline across groups. For unilateral implantation, we observed an initial improvement in PDQ-39SI of 15.55 ± 3.29% (µ ± SE) across both brain targets at 4 months postoperatively. Unilateral STN patients demonstrated greater improvement in PDQ-39SI than GPi patients at 4 and 18 months postoperatively. Analysis of patients with staged bilateral leads revealed an initial 25.34 ± 2.74% (µ ± SE) improvement in PDQ-39SI at 4 months after the first lead with further improvement until 18 months, with no difference across targets. Scores did not improve after the second lead with gradual worsening starting at 18 months postoperatively. STN-DBS provided greater short-term QoL improvement than GPi-DBS for unilateral surgery. For staged bilateral DBS, overall QoL improvement was explained primarily by the first lead. Decision-making for patients considering DBS should include a discussion surrounding the potential risks and benefits from a second DBS lead.

Systemic effects of deep brain stimulation on synergic control in Parkinson's disease

OBJECTIVE

We explored effects of deep brain stimulation (DBS) in patients with Parkinson's disease (PD) on the synergic control of fingers in a multi-finger force production task and of muscles in a task involving vertical posture.

METHODS

The finger task involved the four fingers of a hand producing accurate total force followed by a targeted quick force pulse. The postural task involved releasing a load from extended arms. The analysis of synergies was performed within the framework of the uncontrolled manifold hypothesis.

RESULTS

DBS led to no significant changes in indices of stability during steady-state phases. In contrast, DBS improved indices of agility, quantified as anticipatory synergy adjustments that reduced stability of salient performance variables in preparation to their quick change. There were moderate-to-strong correlations between indices of both stability and agility measured in the multi-finger force production and multi-muscle whole-body action.

CONCLUSIONS

Our results point at systemic changes in synergic control in PD. They show that DBS is effective in improving only one components of synergic control related to agility in performance being relatively ineffective for the stability component.

SIGNIFICANCE

The results show systemic brain mechanisms of synergies and suggest differential effects of DBS on indices of stability and agility.

Effect of Subthalamic Deep Brain Stimulation on Upper Limb Dexterity in Patients with Parkinson Disease

OBJECTIVE

The efficacy of deep brain stimulation (DBS) of the subthalamic nucleus (STN) on dexterity remains controversial despite its recognition as an effective strategy for Parkinson disease. The present study investigated the efficacy of STN-DBS for ameliorating bradykinesia and dexterity compared with dopaminergic medications.

METHODS

Part III of the Unified Parkinson's Disease Rating Scale was used for the evaluation of bradykinesia, whereas the Purdue Pegboard Test and the Box and Block test were selected for dexterity.

RESULTS

Our findings indicate that bradykinesia is significantly improved with both DBS and dopaminergic medication, whereas dexterity is improved only with DBS. Dopaminergic medication did not show a satisfactory efficacy on dexterity, and there was little synergistic effect of dopaminergic medication and STN-DBS for improving dexterity associated with Parkinson disease.

CONCLUSIONS

Our results suggest that DBS is potentially more effective than dopaminergic medications for improving dexterity. The disparities in efficacy for bradykinesia and dexterity between DBS and dopaminergic medication hint at the potential mechanisms of STN-DBS. We speculate that DBS follows at least 2 different mechanisms for improving parkinsonian symptoms: 1) the dopaminergic system, primarily for the improvement of bradykinesia and 2) the nondopaminergic system, for the improvement of dexterity. This hypothesis requires further verification and investigation.

The Dominant-Subthalamic Nucleus Phenomenon in Bilateral Deep Brain Stimulation for Parkinson's Disease: Evidence from a Gait Analysis Study

Background

It has been suggested that parkinsonian [Parkinson’s disease (PD)] patients might have a “dominant” (DOM) subthalamic nucleus (STN), whose unilateral electrical stimulation [deep brain stimulation (DBS)] could lead to an improvement in PD symptoms similar to bilateral STN-DBS.

Objectives

Since disability in PD patients is often related to gait problems, in this study, we wanted to investigate in a group of patients bilaterally implanted for STN-DBS: (1) if it was possible to identify a subgroup of subjects with a dominant STN; (2) in the case, if the unilateral stimulation of the dominant STN was capable to improve gait abnormalities, as assessed by instrumented multifactorial gait analysis, similarly to what observed with bilateral stimulation.

Methods

We studied 10 PD patients with bilateral STN-DBS. A clinical evaluation and a kinematic, kinetic, and electromyographic (EMG) analysis of overground walking were performed—off medication—in four conditions: without stimulation, with bilateral stimulation, with unilateral right or left STN-DBS. Through a hierarchical agglomerative cluster analysis based on motor Unified Parkinson’s Disease Rating Scale scores, it was possible to separate patients into two groups, based on the presence (six patients, DOM group) or absence (four patients, NDOM group) of a dominant STN.

Results

In the DOM group, both bilateral and unilateral stimulation of the dominant STN significantly increased gait speed, stride length, range of motion of lower limb joints, and peaks of moment and power at the ankle joint; moreover, the EMG activation pattern of distal leg muscles was improved. The unilateral stimulation of the non-dominant STN did not produce any significant effect. In the NDOM group, only bilateral stimulation determined a significant improvement of gait parameters.

Conclusion

In the DOM group, the effect of unilateral stimulation of the dominant STN determined an improvement of gait parameters similar to bilateral stimulation. The pre-surgical identification of these patients, if possible, could allow to reduce the surgical risks and side effects of DBS adopting a unilateral approach.

Asymmetric neuromodulation of motor circuits in Parkinson's disease: The role of subthalamic deep brain stimulation

Whereas hemispheric dominance is well-established for appendicular motor control in humans, the evidence for dominance in axial motor control is still scarce. In Parkinson's disease (PD), unilateral (UL) onset of appendicular motor symptoms corresponds with asymmetric neurodegeneration predominantly affecting contralateral nigrostriatal circuits. Disease progression yields bilateral and axial motor symptoms but the initial appendicular asymmetry usually persists. Furthermore, there is evidence for hemispheric dominance for axial motor dysfunction in some of these patients. Dopaminergic medications improve appendicular symptoms but can also produce motor complications over time. Once these complications develop, bilateral (BL) deep brain stimulation (DBS) of the subthalamic nuclei (STN) can significantly improve appendicular symptoms while reducing medication doses and motor complications. Conversely, axial motor symptoms remain a significant source of disability, morbidity, and mortality for patients with PD. These axial symptoms do not necessarily improve with dopaminergic therapy, might not respond, and could even worsen after BL-DBS. In contrast to medications, DBS provides the opportunity to modify stimulation parameters for each cerebral hemisphere. Identical, BL-DBS of motor circuits with hemispheric dominance in PD might produce overstimulation on one side and/or understimulation on the other side, which could contribute to motor dysfunction. Several studies based on asymmetry of appendicular motor symptoms already support an initial UL rather than BL approach to DBS in some patients. The response of axial motor symptoms to UL versus BL-DBS remains unclear. Nonetheless, UL-DBS, staged BL-DBS, or asymmetric programming of BL-DBS could also be considered in patients with PD.

Subthalamic Neurons Encode Both Single- and Multi-Limb Movements in Parkinson's Disease Patients

The subthalamic nucleus (STN) is the main target for neurosurgical treatment of motor signs of Parkinson’s disease (PD). Despite the therapeutic effect on both upper and lower extremities, its role in motor control and coordination and its changes in Parkinson’s disease are not fully clear. We intraoperatively recorded single unit activity in ten patients with PD who performed repetitive feet or hand movements while undergoing implantation of a deep brain stimulator. We found both distinct and overlapping representations of upper and lower extremity movement kinematics in subthalamic units and observed evidence for re-routing to a multi-limb representation that participates in limb coordination. The well-known subthalamic somatotopy showed a large overlap of feet and hand representations in the PD patients. This overlap and excessive amounts of kinematics or coordination units may reflect pathophysiology or compensatory mechanisms. Our findings thus explain, at the single neuron level, the important subthalamic role in motor control and coordination and indicate the effect of PD on the neuronal representation of movement.

Inter-limb coupling during diadochokinesis in Parkinson's and Huntington's disease

Patients with neurodegenerative diseases often exhibit deficits in bimanual coordination. One characteristic of bimanual movements is inter-limb coupling. It is the property of motor performance harmonization between hands during a bimanual task. The objective of this study was to identify whether spatial and temporal inter-limb coupling occurred in Parkinson's disease (PD) and Huntington's disease (HD) patients. Twenty-three PD patients and 15 healthy controls were tested. Data from 12 choreic HD patients were also taken from a databank. Participants were asked to perform a unimanual and bimanual rapid repetitive diadochokinesis task. The difference between hands in mean amplitude and mean duration of cycles was computed in the unimanual and bimanual tasks for each group. Results show that healthy controls exhibited temporal and spatial inter-limb coupling during the bimanual diadochokinesis task. Conversely, PD and HD patients exhibited temporal inter-limb coupling; but failed to exhibit spatial inter-limb coupling during the bimanual diadochokinesis task. Furthermore, HD patients exhibited reduced levels of structural coupling compared to controls and PD patients. These results suggest that alterations in basal ganglia-thalamo-cortical networks due to PD and HD do not affect temporal inter-limb coupling. However, common pathophysiological changes related to PD and HD may cause altered spatial inter-limb coupling during a rapid repetitive bimanual diadochokinesis task.

Acute bouts of assisted cycling improves cognitive and upper extremity movement functions in adolescents with Down syndrome

The aim of this study was to examine the effectiveness of 2 modes of exercise on cognitive and upper extremity movement functioning in adolescents with Down syndrome (DS). Nine participants randomly completed 3 interventions over 3 consecutive weeks. The interventions were: (a) voluntary cycling (VC), in which participants cycled at their self-selected pedaling rate; (b) assisted cycling (AC), in which the participants' voluntary pedaling rates were augmented with a motor to ensure the maintenance of 80 rpm; and (c) no cycling (NC), in which the participants sat and listened to music. Manual dexterity improved after AC, but not after VC or NC. Measures of cognitive function, including reaction time and cognitive planning, also improved after AC, but not after the other interventions. Future research will try to uncover the mechanisms involved in the behavioral improvements found after an acute bout of assisted cycling in adolescents with DS.

Deep brain stimulation in Parkinson's disease

For the last 50 years, levodopa has been the cornerstone of Parkinson's disease management. However, a majority of patients develop motor complications a few years after therapy onset. Deep brain stimulation has been approved by the FDA as an adjunctive treatment in Parkinson disease, especially aimed at controlling these complications. However, the exact mechanism of action of deep brain stimulation, the best nucleus to target as well as the best timing for surgery are still debatable. We here provide an in-depth and critical review of the current literature on this topic.

Deep brain stimulation in Parkinson's disease

For the last 50 years, levodopa has been the cornerstone of Parkinson's disease management. However, a majority of patients develop motor complications a few years after therapy onset. Deep brain stimulation has been approved by the FDA as an adjunctive treatment in Parkinson disease, especially aimed at controlling these complications. However, the exact mechanism of action of deep brain stimulation, the best nucleus to target as well as the best timing for surgery are still debatable. We here provide an in-depth and critical review of the current literature on this topic.

Bimanual force coordination in Parkinson's disease patients with bilateral subthalamic deep brain stimulation

OBJECTIVE

Studies of bimanual actions similar to activities of daily living (ADLs) are currently lacking in evaluating fine motor control in Parkinson's disease patients implanted with bilateral subthalamic deep brain stimulators. We investigated basic time and force characteristics of a bimanual task that resembles performance of ADLs in a group of bilateral subthalamic deep brain stimulation (DBS) patients.

METHODS

Patients were evaluated in three different DBS parameter conditions off stimulation, on clinically derived stimulation parameters, and on settings derived from a patient-specific computational model. Model-based parameters were computed as a means to minimize spread of current to non-motor regions of the subthalamic nucleus via Cicerone Deep Brain Stimulation software. Patients were evaluated off parkinsonian medications in each stimulation condition.

RESULTS

The data indicate that DBS parameter state does not affect most aspects of fine motor control in ADL-like tasks; however, features such as increased grip force and grip symmetry varied with the stimulation state. In the absence of DBS parameters, patients exhibited significant grip force asymmetry. Overall UPDRS-III and UPDRS-III scores associated with hand function were lower while patients were experiencing clinically-derived or model-based parameters, as compared to the off-stimulation condition.

CONCLUSION

While bilateral subthalamic DBS has been shown to alleviate gross motor dysfunction, our results indicate that DBS may not provide the same magnitude of benefit to fine motor coordination.

Deep brain stimulation improves movement amplitude but not hastening of repetitive finger movements

External pacing cues, dopaminergic medication, and bilateral subthalamic nucleus deep brain stimulation (STN-DBS) improve repetitive movements performed at low rates. When the pacing rate is increased to frequencies near 2 Hz and above, both external pacing cues and Parkinson's medication were shown to be ineffective at improving repetitive finger movement performance. It remains unclear if STN-DBS improves the performance of repetitive finger movements at high pacing rates. This study examined the effects of STN-DBS on the amplitude and rate of repetitive finger movement across a range of external pacing rates. Nine participants with STN-DBS (OFF and ON stimulation) and nine matched healthy adults performed repetitive index finger flexion movements paced by an acoustic tone that increased from 1.0 to 3.0 Hz. OFF stimulation, most subjects moved at rates that were substantially higher (hastening pattern) or lower (bradykinesia pattern) than the tone rate, particularly at high pacing rates. ON stimulation, movement rate improved in subjects with the bradykinesia pattern, but not in those with the hastening pattern. Overall, STN-DBS did not significantly affect movement rate. In contrast, STN-DBS significantly (p<0.05) improved movement amplitude across all pacing rates. These findings demonstrate that STN-DBS improves movement amplitude, but had no effect on the rate of movement in participants with a hastening pattern. Separately testing movement amplitude and movement rate using both high and low rate externally paced cues in the clinical environment may aid in the diagnosis and treatment of people with Parkinson's disease.

Effects of aging on force coordination in bimanual task performance

We investigated within- and between-hands grip-load force coordination in both healthy young and older adult participants during bimanual tasks involving realistic actions. Age-related changes in manual behaviors such as grip force production and safety margins were expected in older adults. Within-hand grip-load coordination was expected to decrease with aging during the performance of dynamic actions, but not static actions. The effects of task and hand dominance on task performance were also evaluated. Grip force production increased with age; however, changes in fingertip frictional properties with aging increased the risk of object slip. Indices of within-hand grip-load coordination did not alter with age, but such indices were affected by task goals. The action of connecting two independent objects, particularly with rotational action, was associated with declines in all indices of within- and between-hands force coordination, independent of age. Evidence of task-specific differences in within-hand grip-load coordination in the current data set suggests that individual hand specification emerges and persists with age in everyday bimanual prehension tasks, independent of the action role assigned to the dominant and non-dominant hands.

Force coordination during bimanual task performance in Parkinson's disease

We investigated within- and between-hand grip-load force coordination in medically managed Parkinson's disease (PD) patients during bimanual tasks involving realistic actions. Increased grip force production and evidence of bradykinesia were expected in PD patients. Force coordination indices were also expected to be reduced in PD, due to impaired anticipatory force control. Increased grip force, bradykinesia, and abnormal load force production were exhibited in PD patients as compared to healthy controls. Indices of between-hand load force coordination, but not between-hand grip force coordination, were reduced in PD patients. Discrepancies in the strength of within-hand force coordination with respect to hand action were also noted in PD patients. Increased grip force production, in conjunction with abnormal load force production, may result in reduced fine motor control in PD patients during daily activities. Integrating quantitative analyses of realistic motor function in clinic may assist clinicians in evaluating the effectiveness of medical intervention in PD patients.

Modulation of local field potential power of the subthalamic nucleus during isometric force generation in patients with Parkinson's disease

Investigations of local field potentials of the subthalamic nucleus of patients with Parkinson's disease have provided evidence for pathologically exaggerated oscillatory beta-band activity (13-30 Hz) which is amenable to physiological modulation by, e.g., voluntary movement. Previous functional magnetic resonance imaging studies in healthy controls have provided evidence for an increase of subthalamic nucleus blood-oxygenation-level-dependant signal in incremental force generation tasks. However, the modulation of neuronal activity by force generation and its relationship to peripheral feedback remain to be elucidated. We hypothesised that beta-band activity in the subthalamic nucleus is modulated by incremental force generation. Subthalamic nucleus local field potentials were recorded intraoperatively in 13 patients with Parkinson's disease (37 recording sites) during rest and five incremental isometric force generation conditions of the arm with applied loads of 0-400 g (in 100-g increments). Repeated measures analysis of variance (ANOVA) revealed a modulation of local field potential (LFP) power in the upper beta-band (in 24-30 Hz; F(₃.₀₄₂)=4.693, p=0.036) and the gamma-band (in 70-76 Hz; F(₄)=4.116, p=0.036). Granger-causality was computed with the squared partial directed coherence and showed no significant modulation during incremental isometric force generation. Our findings indicate that the upper beta- and gamma-band power of subthalamic nucleus local field potentials are modulated by the physiological task of force generation in patients with Parkinson's disease. This modulation seems to be not an effect of a modulation of peripheral feedback.

Modulatory effect of subthalamic nucleus on the development of fatigue during exhausting exercise: an in vivo electrophysiological and microdialysis study in rats

The purpose of the study was to investigate the modulatory effect of changes of subthalamic nucleus (STN) activity on the development of central fatigue during exhausting exercise, and reveal the possible mechanism that might affect STN activity from the perspective of neurotransmitters. Rats were randomly divided into electrophysiology and microdialysis study groups. For electrophysiological study, electrical activity in sensorimotor cortex and STN were simultaneously recorded before, during and 90min after the exhausting exercise. For microdialysis study, extracellular fluid of STN was continuously collected with a microdialysis probe and glutamate (Glu), gamma-aminobutyric acid (GABA) levels were subsequently detected with high performance liquid chromatography (HPLC). The behavioral studies showed that rats ran well initiatively with the treadmill exercise in the beginning, 45 ± 11.5min later, movement capacity reduced obviously (which was termed as 'early fatigue'). Correspondingly, STN activity increased significantly compared with rest condition (p < 0.05), while, cortex activity decreased significantly (p < 0.05). Subsequently, rats continued their exercise with minor external stimulation till exhaustion. Cortex activity reached the minimum value under exhaustion condition, while STN activity changed insignificantly (p > 0.05). For microdialysis study, the dynamic change of Glu/GABA ratio was consistent with the change of STN activity during the development of 'early fatigue' rather than the development of exhaustion. In conclusion, the present study shows that, the development of the cortex fatigue during exhausting exercise consists of two phases, 'early fatigue' and exhaustion. Our results suggest that, dynamic changes of STN activity are closely relevant to the development of 'early fatigue' rather than exhaustion, and the changes of STN activity during the development of 'early fatigue' might be partly related to the variance of Glu and GABA levels in STN extracellular fluid. Key pointsThe development of the cortex fatigue during exhausting exercise consists of two phases, 'early fatigue' and exhaustion.Dynamic changes of STN activity are closely relevant to the development of 'early fatigue' rather than exhaustion.The changes of STN activity during the development of 'early fatigue' might be partly related to the variance of Glu and GABA levels in STN extracellular fluid.

Parkinson’s disease DBS: what, when, who and why? The time has come to tailor DBS targets

Deep brain stimulation (DBS) has recently been proven to be an effective therapy for medication refractory symptoms of Parkinson's disease. As the evidence base continues to evolve, many important issues have surfaced, including: what operation should be performed (brain target[s],unilateral vs bilateral, simultaneous vs staged); when to operate (how early is too early to intervene?), who should be operated on (disease duration, age, symptom profiles and the use of the interdisciplinary screening team); and finally, why to operate (the rationale of surgery vs medication/apomorphine pumps/duodopa pumps/stem cell trials/gene therapy trials). We will address each of these critical issues, as well make the argument that a tailored approach to DBS and DBS targeting will best serve each potential candidate. We will review the multiple peer reviewed studies and we will emphasize the recently available data from randomized DBS studies.We will argue that moving away from a single DBS target (e.g., subthalamic nucleus DBS) and a single approach to DBS methodology (e.g., bilateral simultaneous operations) is a reasonable next step for the Parkinson's disease community. Following careful interdisciplinary DBS screening, a physician-patient discussion has the potential to establish a patient-centered and symptom-specific outcome for each potential DBS candidate. The interdisciplinary DBS team can function together to formulate and to consider an optimal and tailored approach. A tailored approach will allow for the consideration of the complex and numerous variables that may contribute to a positive or negative overall DBS outcome. We will review and provide expert commentary on a potential interdisciplinary approach to selecting unilateral or alternatively bilateral subthalamic nucleus or globus pallidus internus DBS. Our approach is aimed to maximize benefit(s) and minimize risk(s) in order to best tailor therapy for an individual patient.

Bilateral subthalamic deep brain stimulation after bilateral pallidal deep brain stimulation for Parkinson's disease

BACKGROUND/OBJECTIVE

Globus pallidus internus (GPi) and subthalamic nucleus (STN) have successfully been targeted independently for deep brain stimulator (DBS) placement in medically intractable Parkinson's disease (PD). Bilateral implantation of STN DBS in a patient with preexisting, functioning GPi DBS to specifically treat motor fluctuations is, to our knowledge, yet unreported.

CLINICAL PRESENTATION

We present a case of PD who had well-placed bilateral GPi DBS that controlled dyskinesia effectively and improved the motor symptoms like rigidity and akinesia. It did not improve her motor fluctuations and failed to reduce her medications.

METHODS

We implanted bilateral STN DBS, which improved her 'on' time, reduced her medications and improved her motor scores.

RESULTS/CONCLUSION

In this report we discuss the rationale, technical issues, programming nuances and outcome in a patient with preexisting bilateral GPi DBS who was implanted with bilateral STN DBS.

Activation of subthalamic neurons by contralateral subthalamic deep brain stimulation in Parkinson disease

Multiple studies have shown bilateral improvement in motor symptoms in Parkinson disease (PD) following unilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) and internal segment of the globus pallidus, yet the mechanism(s) underlying this phenomenon are poorly understood. We hypothesized that STN neuronal activity is altered by contralateral STN DBS. This hypothesis was tested intraoperatively in humans with advanced PD using microelectrode recordings of the STN during contralateral STN DBS. We demonstrate alterations in the discharge pattern of STN neurons in response to contralateral STN DBS including short latency, temporally precise, stimulation frequency-independent responses consistent with antidromic activation. Furthermore, the total discharge frequency during contralateral high frequency stimulation (160 Hz) was greater than during low frequency stimulation (30 Hz) and the resting state. These findings demonstrate complex responses to DBS and imply that output activation throughout the basal ganglia-thalamic-cortical network rather than local inhibition is a therapeutic mechanism of DBS.

The use of kinetics as a marker for manual dexterity after stroke and stroke recovery

Stroke is the leading cause of severe, long-term disability among older adults in the United States. Unimanual motor performance of the hemiparetic limb is clearly compromised, and these declines are well documented. An often overlooked aspect of motor function for patients with stroke is the effect of unilateral motor dysfunction on bimanual motor activities. Diminished bimanual function resulting from upper extremity hemiparesis necessarily limits the patient's daily functioning. In this review we describe a bimanual dexterity task that replicates many daily activities and outline how kinetic analysis of this task may provide insight into diminished bimanual function of patients with stroke and how these variables may be useful in assessing level of recovery and rate of motor recovery associated with behavioral interventions intended to improve upper extremity function. It is argued that the use of objective kinetic measures to quantify hand function may facilitate the clinical adoption of behavioral interventions for stroke, such as constraint-induced movement therapy and other repetitive task practice-based interventions.

Forced, Not Voluntary, Exercise Improves Motor Function in Parkinson's Disease Patients

Background. Animal studies indicate forced exercise (FE) improves overall motor function in Parkinsonian rodents. Global improvements in motor function following voluntary exercise (VE) are not widely reported in human Parkinson's disease (PD) patients. Objective. The aim of this study was to compare the effects of VE and FE on PD symptoms, motor function, and bimanual dexterity. Methods. Ten patients with mild to moderate PD were randomly assigned to complete 8 weeks of FE or VE. With the assistance of a trainer, patients in the FE group pedaled at a rate 30% greater than their preferred voluntary rate, whereas patients in the VE group pedaled at their preferred rate. Aerobic intensity for both groups was identical, 60% to 80% of their individualized training heart rate. Results. Aerobic fitness improved for both groups. Following FE, Unified Parkinson's Disease Rating Scale (UPDRS) motor scores improved 35%, whereas patients completing VE did not exhibit any improvement. The control and coordination of grasping forces during the performance of a functional bimanual dexterity task improved significantly for patients in the FE group, whereas no changes in motor performance were observed following VE. Improvements in clinical measures of rigidity and bradykinesia and biomechanical measures of bimanual dexterity were maintained 4 weeks after FE cessation. Conclusions. Aerobic fitness can be improved in PD patients following both VE and FE interventions. However, only FE results in significant improvements in motor function and bimanual dexterity. Biomechanical data indicate that FE leads to a shift in motor control strategy, from feedback to a greater reliance on feedforward processes, which suggests FE may be altering central motor control processes.

Bilateral subthalamic stimulation impairs cognitive-motor performance in Parkinson's disease patients

Deep brain stimulation (DBS) is a surgical procedure that has been shown effective in improving the cardinal motor signs of advanced Parkinson's disease, however, declines in cognitive function have been associated with bilateral subthalamic nucleus (STN) DBS. Despite the fact that most activities of daily living clearly have motor and cognitive components performed simultaneously, postoperative assessments of cognitive and motor function occur, in general, in isolation of one another. The primary aim of this study was to determine the effects of unilateral and bilateral STN DBS on upper extremity motor function and cognitive performance under single- and dual-task conditions in advanced Parkinson's disease patients. Data were collected from eight advanced Parkinson's disease patients between the ages of 48 and 70 years (mean 56.5) who had bilaterally placed STN stimulators. Stimulation parameters for DBS devices were optimized clinically and were stable for at least 6 months prior to study participation. Data were collected while patients were Off anti-parkinsonian medications under three stimulation conditions: Off stimulation, unilateral DBS and bilateral DBS. In each stimulation condition patients performed a cognitive (n-back task) and motor (force tracking) task under single- and dual-task conditions. During dual-task conditions, patients performed the n-back and force-maintenance task simultaneously. Under relatively simple dual-task conditions there were no differences in cognitive or motor performance under unilateral and bilateral stimulation. As dual-task complexity increased, cognitive and motor performance was significantly worse with bilateral compared with unilateral stimulation. In the most complex dual-task condition (i.e. 2-back + force tracking), bilateral stimulation resulted in a level of motor performance that was similar to the Off stimulation condition. Significant declines in cognitive and motor function under modest dual-task conditions with bilateral but not with unilateral STN DBS suggest that unilateral procedures may be an alternative to bilateral DBS for some patients, in particular, those with asymmetric symptomology. From a clinical perspective, these results underscore the need to assess cognitive and motor function simultaneously during DBS programming as these conditions may better reflect the context in which daily activities are performed.

Are two leads always better than one: an emerging case for unilateral subthalamic deep brain stimulation in Parkinson's disease

Bilateral subthalamic (STN) deep brain stimulation (DBS) provides significant symptom relief for the majority of well-screened patients suffering with Parkinson's disease (PD). Implantation of stimulating electrodes bilaterally in a single session has become standard in most operating theaters worldwide. There is, however, limited evidence-based support for this approach. Although bilateral surgical procedures have been shown, using standardized clinical ratings, to provide greater motor benefits compared to unilateral procedures, bilateral procedures are more likely to be associated with increased acute and long-term complications including post-operative confusion, speech difficulties and cognitive dysfunction. Unilateral stimulation has been shown to provide significant benefits for appendicular and axial symptoms. The relative benefit of implanting one versus two sides and whether the degree of benefit associated with the second side is worth the potential risk of doing so have not been examined systematically. The relative magnitude of benefit associated with unilateral versus bilateral procedures is likely to vary from patient to patient, particularly in those patients with asymmetric symptomatology. As such, there are likely subsets of patients who do not require and therefore should not be exposed to the potential complications associated with bilateral simultaneous implantation. This review and commentary will outline our current understanding of the benefits associated with unilateral and bilateral STN DBS and discuss the role of unilateral or staged unilateral procedures as an alternative surgical approach for patients with advanced PD.