Effect of subthalamic deep brain stimulation on turning kinematics and related saccadic eye movements in Parkinson disease

The effect of deep brain stimulation on lower extremity dexterity in people with Parkinson's disease

PURPOSE

To examine the effect of deep brain stimulation (DBS) on lower extremity dexterity in people with Parkinson's disease (PwPD) and to investigate the relationship between this effect and the effect of DBS on measures of different walking characteristics, and other features of Parkinson's disease.

MATERIALS AND METHODS

Thirty-six PwPD were included. Assessment was performed twice with DBS "on" and DBS "off" state.

RESULTS

The LEDT scores of both extremities, the Unified Parkinson Disease Rating Scale-motor section (UPDRS-III), the 10-Meter Walk Test (TMWT), the Timed Up and Go Test (TUG), the Figure-of-Eight Walk Test (FEWT), and the Three-Meter Backward Walk Test (TMBWT) scores were significantly better in "on" DBS condition than "off" DBS condition. The effect of DBS on lower extremity dexterity is related to age and levodopa equivalent daily dosage (LEDD). The effect of DBS on lower extremity dexterity and the effect of DBS on the bradykinesia, TUG, the FEWT, and the TMBWT were also related.

CONCLUSIONS

DBS has a positive effect on lower extremity dexterity. Clinical characteristics such as age and LEDD and the effect of DBS on bradykinesia, walking with turning, curved walking, and backward walking is related with the effect of DBS on lower extremity dexterity.

Impact of deep brain stimulation on gait in Parkinson disease: A kinematic study

BACKGROUND

The effect of Deep Brain Stimulation (DBS) on gait in Parkinson's Disease (PD) is poorly understood. Kinematic studies utilizing quantitative gait outcomes such as speed, cadence, and stride length have shown mixed results and were done mostly before and after acute DBS discontinuation.

OBJECTIVE

To examine longitudinal changes in kinematic gait outcomes before and after DBS surgery.

METHOD

We retrospectively assessed changes in quantitative gait outcomes via motion capture in 22 PD patients before and after subthalamic (STN) or globus pallidus internus (GPi) DBS, in on medication state. Associations between gait outcomes and clinical variables were also assessed.

RESULT

Gait speed reduced from 110.7 ± 21.3 cm/s before surgery to 93.6 ± 24.9 after surgery (7.7 ± 2.9 months post-surgery, duration between assessments was 15.0 ± 3.8 months). Cadence, step length, stride length, and single support time reduced, while total support time, and initial double support time increased. Despite this, there was overall improvement in the Movement Disorder Society-Unified Parkinson Disease Rating Scale-Part III score "on medication/on stimulation" score (from 19.8 ± 10.7-13.9 ± 8.6). Change of gait speed was not related to changes in levodopa dosage, disease duration, unilateral vs bilateral stimulation, or target nucleus.

CONCLUSION

Quantitative gait outcomes in on medication state worsened after chronic DBS therapy despite improvement in other clinical outcomes. Whether these changes reflect the effects of DBS as opposed to ongoing disease progression is unknown.

Medication only improves limb movements while deep brain stimulation improves eye and limb movements during visually-guided reaching in Parkinson's disease

Background

Antiparkinson medication and subthalamic nucleus deep brain stimulation (STN-DBS), two common treatments of Parkinson's disease (PD), effectively improve skeletomotor movements. However, evidence suggests that these treatments may have differential effects on eye and limb movements, although both movement types are controlled through the parallel basal ganglia loops.

Objective

Using a task that requires both eye and upper limb movements, we aimed to determine the effects of medication and STN-DBS on eye and upper limb movement performance.

Methods

Participants performed a visually-guided reaching task. We collected eye and upper limb movement data from participants with PD who were tested both OFF and ON medication (n = 34) or both OFF and ON bilateral STN-DBS while OFF medication (n = 11). We also collected data from older adult healthy controls (n = 14).

Results

We found that medication increased saccade latency, while having no effect on reach reaction time (RT). Medication significantly decreased saccade peak velocity, while increasing reach peak velocity. We also found that bilateral STN-DBS significantly decreased saccade latency while having no effect on reach RT, and increased saccade and reach peak velocity. Finally, we found that there was a positive relationship between saccade latency and reach RT, which was unaffected by either treatment.

Conclusion

These findings show that medication worsens saccade performance and benefits reaching performance, while STN-DBS benefits both saccade and reaching performance. We explore what the differential beneficial and detrimental effects on eye and limb movements suggest about the potential physiological changes occurring due to treatment.

Novel ways to modulate the vestibular system: Magnetic vestibular stimulation, deep brain stimulation and transcranial magnetic stimulation / transcranial direct current stimulation

BACKGROUND

Advances in neurotechnologies are revolutionizing our understanding of complex neural circuits and enabling new treatments for disorders of the human brain. In the vestibular system, electromagnetic stimuli can now modulate vestibular reflexes and sensations of self-motion by artificially stimulating the labyrinth, cerebellum, cerebral cortex, and their connections.

OBJECTIVE

In this narrative review, we describe evolving neuromodulatory techniques including magnetic vestibular stimulation (MVS), deep brain stimulation (DBS), transcranial magnetic stimulation (TMS), and transcranial direct-current stimulation (tDCS) and discuss current and potential future application in the field of neuro-otology.

RESULTS

MVS triggers both vestibular nystagmic (persistent) and perceptual (lasting ∼1 min) responses that may serve as a model to study central adaptational mechanisms and pathomechanisms of hemispatial neglect. By systematically mapping DBS electrodes, targeted stimulation of central vestibular pathways allowed modulating eye movements, vestibular heading perception, spatial attention and graviception, resulting in reduced anti-saccade error rates and hypometria, improved heading discrimination, shifts in verticality perception and transiently decreased spatial attention. For TMS/tDCS treatment trials have demonstrated amelioration of vestibular symptoms in various neuro-otological conditions, including chronic vestibular insufficiency, Mal-de-Debarquement and cerebellar ataxia.

CONCLUSION

Neuromodulation has a bright future as a potential treatment of vestibular dysfunction. MVS, DBS and TMS may provide new and sophisticated, customizable, and specific treatment options of vestibular symptoms in humans. While promising treatment responses have been reported for TMS/tDCS, treatment trials for vestibular disorders using MVS or DBS have yet to be defined and performed.

Troubleshooting Gait Disturbances in Parkinson's Disease With Deep Brain Stimulation

Deep brain stimulation (DBS) of the subthalamic nucleus or the globus pallidus is an established treatment for Parkinson's disease (PD) that yields a marked and lasting improvement of motor symptoms. Yet, DBS benefit on gait disturbances in PD is still debated and can be a source of dissatisfaction and poor quality of life. Gait disturbances in PD encompass a variety of clinical manifestations and rely on different pathophysiological bases. While gait disturbances arising years after DBS surgery can be related to disease progression, early impairment of gait may be secondary to treatable causes and benefits from DBS reprogramming. In this review, we tackle the issue of gait disturbances in PD patients with DBS by discussing their neurophysiological basis, providing a detailed clinical characterization, and proposing a pragmatic programming approach to support their management.

Late-cueing of gait tasks on an uneven brick surface impacts coordination and center of mass control in older adults

BACKGROUND

Changing directions while walking (turning gait), often with little planning time, is essential to navigating irregular surfaces in the built-environment. It is unclear how older adults reorient their bodies under these constraints and whether adaptations are related to declines in physiological characteristics.

RESEARCH QUESTION

The aims of this study were to (1) investigate whether surface irregularity, late-cueing, and age negatively affect coordination, kinematics, and center of mass (COM) movement during 90° turning gait and (2) determine if adaptations correlate with declines in strength, balance, and reaction-time.

METHODS

Eighteen young (18-35 years) and sixteen older (65+ years) healthy adults participated in the study. Retro-reflective marker and trunk-accelerometry data were used to compute upper-body segmental reorientation timing, upper-body kinematics, and COM movement characteristics. Balance scores, lower-limb strength, and choice-reaction-times were also recorded.

RESULTS

Young and older adults maintained a cranial-caudal (head, shoulders, pelvis) reorientation sequence (p ≤ 0.018), lowered head pitch (uneven surface; young p = 0.035 and old p < 0.001), increased maximum COM acceleration (uneven surface and late-cueing; p ≤ 0.002), and decreased COM smoothness (uneven surface; p < 0.001). Young adults increased shoulder roll (uneven surface and late-cueing; p ≤ 0.008). Reduced stride regularity (late-cueing) was observed in older (p < 0.001), compared to young (p = 0.017), adults. Declines in strength (p ≤ 0.040) and balance (p = 0.018) were correlated with gait adaptations of older adults.

SIGNIFICANCE

Late-cueing on an uneven surface is challenging for older adults. These challenges are exacerbated by strength and balance deficits.

The Relationship between Saccades and Locomotion

Human locomotion involves a complex interplay among multiple brain regions and depends on constant feedback from the visual system. We summarize here the current understanding of the relationship among fixations, saccades, and gait as observed in studies sampling eye movements during locomotion, through a review of the literature and a synthesis of the relevant knowledge on the topic. A significant overlap in locomotor and saccadic neural circuitry exists that may support this relationship. Several animal studies have identified potential integration nodes between these overlapping circuitries. Behavioral studies that explored the relationship of saccadic and gait-related impairments in normal conditions and in various disease states are also discussed. Eye movements and locomotion share many underlying neural circuits, and further studies can leverage this interplay for diagnostic and therapeutic purposes.

Pace of movement: the role of single neurons in the subthalamic nucleus

OBJECTIVE

The ability to modulate the pace of movement is a critical factor in the smooth operation of the motor system. The authors recently described distinct and overlapping representations of movement kinematics in the subthalamic nucleus (STN), but it is still unclear how movement pace is modulated according to the demands of the task at the neuronal level in this area. The goal of this study was to clarify how different movement paces are being controlled by neurons in the STN.

METHODS

The authors performed direct recording of the electrical activity of single neurons in the STN of neurosurgical patients with Parkinson's disease undergoing implantation of a deep brain stimulator under local anesthesia while the patients performed repetitive foot and hand movements intraoperatively at multiple paces.

RESULTS

A change was observed in the neuronal population controlling the movement for each pace. The mechanism for switching between these controlling populations differs for hand and foot movements.

CONCLUSIONS

These findings suggest that disparate schemes are utilized in the STN for neuronal recruitment for motor control of the upper and lower extremities. The results indicate a distributed model of motor control within the STN, where the active neuronal population changes when modifying the task condition and pace.

Bilateral deep brain stimulation of the subthalamic nucleus increases pointing error during memory-guided sequential reaching

Deep brain stimulation of the subthalamic nucleus (STN DBS) significantly improves clinical motor symptoms, as well as intensive aspects of movement like velocity and amplitude in patients with Parkinson's disease (PD). However, the effects of bilateral STN DBS on integrative and coordinative aspects of motor control are equivocal. The aim of this study was to investigate the effects of bilateral STN DBS on integrative and coordinative aspects of movement using a memory-guided sequential reaching task. The primary outcomes were eye and finger velocity and end-point error. We expected that bilateral STN DBS would increase reaching velocity. More importantly, we hypothesized that bilateral STN DBS would increase eye and finger end-point error and this would not simply be the result of a speed accuracy trade-off. Ten patients with PD and bilaterally implanted subthalamic stimulators performed a memory-guided sequential reaching task under four stimulator conditions (DBS-OFF, DBS-LEFT, DBS-RIGHT, and DBS-BILATERAL) over 4 days. DBS-BILATERAL significantly increased eye velocity compared to DBS-OFF, DBS-LEFT, and DBS-RIGHT. It also increased finger velocity compared to DBS-OFF and DBS-RIGHT. DBS-BILATERAL did not change eye end-point error. The novel finding was that DBS-BILATERAL increased finger end-point error compared to DBS-OFF, DBS-LEFT, and DBS-RIGHT even after adjusting for differences in velocity. We conclude that bilateral STN DBS may facilitate basal ganglia-cortical networks that underlie intensive aspects of movement like velocity, but it may disrupt selective basal ganglia-cortical networks that underlie certain integrative and coordinative aspects of movement such as spatial accuracy.

Subthalamic nucleus stimulation and gait in Parkinson's Disease: a not always fruitful relationship

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) provides efficient treatment for the alleviation of motor signs in patients with advanced Parkinson's disease (PD), but its specific effects on gait is sometimes less successful as it may even lead to an aggravation of freezing of gait. To better understand when axial symptoms can be expected to improve and when they may worsen or be resistant to STN-DBS, we propose here a narrative review that considers the recent literature evidences based on instrumental gait analysis data. Our aim is to report about the efficacy of STN-DBS on PD gait, analyzing the clinical and procedural factors involved, and discussing the strategies for optimizing such effectiveness in patients with advanced PD.

What do eye movements tell us about patients with neurological disorders? - An introduction to saccade recording in the clinical setting

Non-invasive and readily implemented in the clinical setting, eye movement studies have been conducted extensively not only in healthy human subjects but also in patients with neurological disorders. The purpose of saccade studies is to "read out" the pathophysiology underlying neurological disorders from the saccade records, referring to known primate physiology. In the current review, we provide an overview of studies in which we attempted to elucidate the patterns of saccade abnormalities in over 250 patients with neurological disorders, including cerebellar ataxia and brainstem pathology due to neurodegenerative disorders, and what they tell about the pathophysiology of patients with neurological disorders. We also discuss how interventions, such as deep brain stimulation, affect saccade performance and provide further insights into the workings of the oculomotor system in humans. Finally, we argue that it is important to understand the functional significance and behavioral correlate of saccade abnormalities in daily life, which could require eye tracking methodologies to be performed in settings similar to daily life.

Eye movements and deep brain stimulation

PURPOSE OF REVIEW

Deep brain stimulation (DBS) is an established treatment for several neurological conditions, and is most commonly used to treat Parkinson's disease by implanting electrodes in the basal ganglia. Despite the fact that circuits involved in eye movement control traverse the basal ganglia and are thus likely to be affected by DBS, studies combining DBS with eye movement analysis have been infrequent. This review focuses on recent research studies that examine the relationship between DBS and various types of eye movements and which highlight the potential of this approach.

RECENT FINDINGS

Recent work shows that DBS in the subthalamic nucleus (STN) can improve smooth pursuit in Parkinson's disease. STN DBS has also been shown to modulate visuospatial attention, and has provided experimental evidence backing a Bayesian model of basal ganglia function. DBS in the pallidum can improve antisaccadic performance in Parkinson's disease, suggesting improvement in higher control of oculomotor function, and implying retrograde striatal stimulation as part of the mechanism of action.

SUMMARY

These studies show that the combination of DBS with eye movement analysis is a powerful research tool. It may be used to study oculomotor physiology, basal ganglia pathophysiology, and the mechanism of action of DBS.

STN-DBS Reduces Saccadic Hypometria but Not Visuospatial Bias in Parkinson's Disease Patients

In contrast to its well-established role in alleviating skeleto-motor symptoms in Parkinson's disease, little is known about the impact of deep brain stimulation (DBS) of the subthalamic nucleus (STN) on oculomotor control and attention. Eye-tracking data of 17 patients with left-hemibody symptom onset was compared with 17 age-matched control subjects. Free-viewing of natural images was assessed without stimulation as baseline and during bilateral DBS. To examine the involvement of ventral STN territories in oculomotion and spatial attention, we employed unilateral stimulation via the left and right ventralmost contacts respectively. When DBS was off, patients showed shorter saccades and a rightward viewing bias compared with controls. Bilateral stimulation in therapeutic settings improved saccadic hypometria but not the visuospatial bias. At a group level, unilateral ventral stimulation yielded no consistent effects. However, the evaluation of electrode position within normalized MNI coordinate space revealed that the extent of early exploration bias correlated with the precise stimulation site within the left subthalamic area. These results suggest that oculomotor impairments "but not higher-level exploration patterns" are effectively ameliorable by DBS in therapeutic settings. Our findings highlight the relevance of the STN topography in selecting contacts for chronic stimulation especially upon appearance of visuospatial attention deficits.

Brain activation underlying turning in Parkinson's disease patients with and without freezing of gait: a virtual reality fMRI study

BACKGROUND

Freezing of gait is a debilitating symptom affecting many patients with Parkinson's disease (PD), causing severe immobility and decreased quality of life. Turning is known to be the most common trigger for freezing and also causes the highest rates of falls. However, the pathophysiological basis for these effects is not well understood.

METHODS

This study used a virtual reality paradigm in combination with functional magnetic resonance imaging to explore the neural correlates underlying turning in 17 PD patients with freezing of gait (FOG) and 10 PD patients without FOG while off their dopaminergic medication. Participants used foot pedals to navigate a virtual environment, which allowed for blood oxygen level-dependent (BOLD) responses and footstep latencies to be compared between periods of straight "walking" and periods of turning through 90°. BOLD data were then analyzed using a mixed effects analysis.

RESULTS

Within group similarities revealed that overall, PD patients with freezing relied heavily on cortical control to enable effective stepping with increased visual cortex activation during turning. Between groups differences showed that when turning, patients with freezing preferentially activated inferior frontal regions that have been implicated in the recruitment of a putative stopping network. In addition, freezers failed to activate premotor and superior parietal cortices. Finally, increased task-based functional connectivity was found in subcortical regions associated with gait and stopping within the freezers group during turning.

CONCLUSIONS

These findings suggest that an increased propensity towards stopping in combination with reduced sensorimotor integration may underlie the neurobiology of freezing of gait during turning.

Fast gaze reorientations by combined movements of the eye, head, trunk and lower extremities

Large reorientations of the line of sight, involving combined rotations of the eyes, head, trunk and lower extremities, are executed either as fast single-step or as slow multiple-step gaze transfers. In order to obtain more insight into the mechanisms of gaze and multisegmental movement control, we have investigated time-optimal gaze shifts (i.e. with the instruction to move as fast as possible) during voluntary whole-body rotations to remembered targets up to 180° eccentricity performed by standing healthy humans in darkness. Fast, accurate, single-step movement patterns occurred in approximately 70 % of trials, i.e. considerably more frequently than in previous studies with the instruction to turn at freely chosen speed (30 %). Head-in-space velocity in these cases was significantly higher than during multiple-step transfers and displayed a conspicuously regular bell-shaped profile, increasing smoothly to a peak and then decreasing slowly until realignment with the target. Head-in-space acceleration was on average not different during reorientations to the different target eccentricities. In contrast, head-in-space velocity increased with target eccentricity due to the longer duration of the acceleration phase implemented during trials to more distant targets. Eye saccade amplitude approached the eye-in-orbit mechanical limit and was unrelated to eye/head velocity, duration or target eccentricity. Overall, the combined movement was stereotyped such that the first two principal components accounted for data variance almost up to gaze shift end, suggesting that the three mechanical degrees of freedom under consideration (eye-in-orbit, head-on-trunk and trunk-in-space) are on average reduced to two kinematic degrees of freedom (i.e. eye, head-in-space). Synchronous EMG activity in the anterior tibial and gastrocnemius muscles preceded the onset of eye rotation. Since the magnitude and timing of peak head-in-space velocity were scaled with target eccentricity and because head-on-trunk and trunk-in-space displacements were on average linearly correlated, we propose a separate controller for head-in-space movement, whereas the movement of the eye-in-space may be, in contrast, governed by global, i.e. gaze feedback. The rapid progression of the line of sight can be sustained, and the reactivation of the vestibulo-ocular reflex would be postponed, until gaze error approaches zero only in association with a strong head-in-space neural control signal.

A protocol to examine vision and gait in Parkinson's disease: impact of cognition and response to visual cues

Background

Cognitive and visual impairments are common in Parkinson’s disease (PD) and contribute to gait deficit and falls. To date, cognition and vision in gait in PD have been assessed separately. Impact of both functions (which we term ‘visuo-cognition’) on gait however is likely interactive and can be tested using visual sampling (specifically saccadic eye movements) to provide an online behavioural measure of performance. Although experiments using static paradigms show saccadic impairment in PD, few studies have quantified visual sampling during dynamic motor tasks such as gait.

This article describes a protocol developed for testing visuo-cognition during gait in order to examine the: 1) independent roles of cognition and vision in gait in PD, 2) interaction between both functions, and 3) role of visuo-cognition in gait in PD.

Methods

Two groups of older adults (≥50 years old) were recruited; non-demented people with PD (n=60) and age-matched controls (n=40). Participants attended one session and a sub-group (n=25) attended two further sessions in order to establish mobile eye-tracker reliability. Participants walked in a gait laboratory under different attentional (single and dual task), environmental (walk straight, through a door and turning), and cueing (no visual cues and visual cues) conditions. Visual sampling was recorded using synchronised mobile eye-tracker and electrooculography systems, and gait was measured using 3D motion analysis.

Discussion

This exploratory study examined visuo-cognitive processes and their impact on gait in PD. Improved understanding of the influence of cognitive and visual functions on visual sampling during gait and gait in PD will assist in development of interventions to improve gait and reduce falls risk. This study will also help establish robust mobile eye-tracking methods in older adults and people with PD.

Effects of deep brain stimulation of the subthalamic nucleus on freezing of gait in Parkinson's disease: a prospective controlled study

BACKGROUND

Freezing of gait (FOG) is a debilitating gait disorder in Parkinson's disease (PD) with partial responsiveness to dopaminergic medication. To date, notions about the effects of subthalamic deep brain stimulation (STN-DBS) on FOG remain controversial.

OBJECTIVES

To compare the effects of bilateral STN-DBS and continued best medical treatment (BMT) on FOG occurrence, FOG severity and clinical outcomes in PD patients at 6 and 12 months follow-up.

METHODS

In this prospective, controlled study, 41 PD patients with at least 5 years disease duration participated. Twenty-four subjects (20 with FOG) were treated with STN-DBS and seventeen (15 with FOG) continued BMT. The primary outcome was the New Freezing of Gait Questionnaire (NFOGQ) at 6 months postsurgery. Other outcomes were the NFOGQ at 12 months and clinical outcomes (Unified Parkinson's Disease Rating Scale III (UPDRS III), timed gait, falls and quality of life) at both time points.

RESULTS

STN-DBS increased the likelihood to convert from being a freezer to a non-freezer at 6 and 12 months follow-up (relative risk reduction=0.4). However, 45% of baseline freezers still experienced FOG 6 and 12 months postsurgery although with reduced severity. Three baseline non-freezers (1/2 BMT-treated, 2/4 STN-DBS-treated) developed FOG during follow-up. STN-DBS-induced benefits on FOG were mostly mediated by baseline levodopa equivalent dose, altered medication-intake and reduced motor fluctuations.

CONCLUSIONS

In contrast to continued BMT, STN-DBS reduced FOG occurrence and severity at 6 months postsurgery with largely sustained effects at 12 months follow-up. Longer follow-up periods are needed to test whether FOG improvements after STN-DBS persist with disease progression.

Dynamic control of posture across locomotor tasks

Successful locomotion depends on postural control to establish and maintain appropriate postural orientation of body segments relative to one another and to the environment and to ensure dynamic stability of the moving body. This article provides a framework for considering dynamic postural control, highlighting the importance of coordination, consistency, and challenges to postural control posed by various locomotor tasks, such as turning and backward walking. The impacts of aging and various movement disorders on postural control are discussed broadly in an effort to provide a general overview of the field and recommendations for assessment of dynamic postural control across different populations in both clinical and research settings. Suggestions for future research on dynamic postural control during locomotion also are provided and include discussion of opportunities afforded by new and developing technologies, the need for long-term monitoring of locomotor performance in everyday activities, gaps in our knowledge of how targeted intervention approaches modify dynamic postural control, and the relative paucity of literature regarding dynamic postural control in movement disorder populations other than Parkinson's disease.

Basal ganglia neuronal activity during scanning eye movements in Parkinson's disease

The oculomotor role of the basal ganglia has been supported by extensive evidence, although their role in scanning eye movements is poorly understood. Nineteen Parkinsońs disease patients, which underwent implantation of deep brain stimulation electrodes, were investigated with simultaneous intraoperative microelectrode recordings and single channel electrooculography in a scanning eye movement task by viewing a series of colored pictures selected from the International Affective Picture System. Four patients additionally underwent a visually guided saccade task. Microelectrode recordings were analyzed selectively from the subthalamic nucleus, substantia nigra pars reticulata and from the globus pallidus by the WaveClus program which allowed for detection and sorting of individual neurons. The relationship between neuronal firing rate and eye movements was studied by crosscorrelation analysis. Out of 183 neurons that were detected, 130 were found in the subthalamic nucleus, 30 in the substantia nigra and 23 in the globus pallidus. Twenty percent of the neurons in each of these structures showed eye movement-related activity. Neurons related to scanning eye movements were mostly unrelated to the visually guided saccades. We conclude that a relatively large number of basal ganglia neurons are involved in eye motion control. Surprisingly, neurons related to scanning eye movements differed from neurons activated during saccades suggesting functional specialization and segregation of both systems for eye movement control.

Subthalamic deep brain stimulation improves smooth pursuit and saccade performance in patients with Parkinson's disease

Background

Deep brain stimulation (DBS) in the subthalamic nucleus (STN) significantly reduces symptoms of Parkinson’s disease (PD) such as bradykinesia, tremor and rigidity. It also reduces the need for anti-PD medication, and thereby potential side-effects of _L-Dopa. Although DBS in the STN is a highly effective therapeutic intervention in PD, its mechanism and effects on oculomotor eye movement control and particularly smooth pursuit eye movements have to date rarely been investigated. Furthermore, previous reports provide conflicting information. The aim was to investigate how DBS in STN affected oculomotor performance in persons with PD using novel analysis techniques.

Methods

Twenty-five patients were eligible (22 males, 3 females) according to the clinical inclusion criteria: idiopathic PD responsive to _L-Dopa and having had bilateral STN stimulation for at least one year to ensure stable DBS treatment. Fifteen patients were excluded due to the strict inclusion criteria applied to avoid interacting and confounding factors when determining the effects of DBS applied alone without PD medication. One patient declined participation. Nine PD patients (median age 63, range 59–69 years) were assessed after having their PD medications withdrawn overnight. They were examined with DBS ON and OFF, with the ON/OFF order individually randomized.

Results

DBS ON increased smooth pursuit velocity accuracy (p < 0.001) and smooth pursuit gain (p = 0.005), especially for faster smooth pursuits (p = 0.034). DBS ON generally increased saccade amplitude accuracy (p = 0.007) and tended to increase peak saccade velocity also (p = 0.087), specifically both saccade velocity and amplitude accuracy for the 20 and 40 degree saccades (p < 0.05). Smooth pursuit latency tended to be longer (p = 0.090) approaching normal with DBS ON. Saccade latency was unaffected.

Conclusions

STN stimulation from DBS alone significantly improved both smooth pursuit and saccade performance in patients with PD. The STN stimulation enhancement found for oculomotor performance suggests clear positive implications for patients’ ability to perform tasks that rely on visual motor control and visual feedback. The new oculomotor analysis methods provide a sensitive vehicle to detect subtle pathological modifications from PD and the functional enhancements produced by STN stimulation from DBS alone.

Cerebral blood flow responses to dorsal and ventral STN DBS correlate with gait and balance responses in Parkinson's disease

OBJECTIVES

The effects of subthalamic nucleus (STN) deep brain stimulation (DBS) on gait and balance vary and the underlying mechanisms remain unclear. DBS location may alter motor benefit due to anatomical heterogeneity in STN. The purposes of this study were to (1) compare the effects of DBS of dorsal (D-STN) versus ventral (V-STN) regions on gait, balance and regional cerebral blood flow (rCBF) and (2) examine the relationships between changes in rCBF and changes in gait and balance induced by D-STN or V-STN DBS.

METHODS

We used a validated atlas registration to locate and stimulate through electrode contacts in D-STN and V-STN regions of 37 people with Parkinson's disease. In a within-subjects, double-blind and counterbalanced design controlled for DBS settings, we measured PET rCBF responses in a priori regions of interest and quantified gait and balance during DBS Off, unilateral D-STN DBS and unilateral V-STN DBS.

RESULTS

DBS of either site increased stride length without producing significant group-level changes in gait velocity, cadence or balance. Both sites increased rCBF in subcortical regions and produced variable changes in cortical and cerebellar regions. DBS-induced changes in gait velocity are related to premotor cortex rCBF changes during V-STN DBS (r=-0.40, p=0.03) and to rCBF changes in the cerebellum anterior lobe during D-STN DBS (r=-0.43, p=0.02).

CONCLUSIONS

DBS-induced changes in gait corresponded to rCBF responses in selected cortical and cerebellar regions. These relationships differed during D-STN versus V-STN DBS, suggesting DBS acts through distinct neuronal pathways dependent on DBS location.