Effects of deep brain stimulation frequency on eye movements and cognitive control.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment for Parkinson's disease (PD). Varying the frequency DBS has differential effects on axial and distal limb functions, suggesting differing modulation of relevant pathways. The STN is also a critical node in oculomotor and associative networks, but the effect of stimulation frequency on these networks remains unknown. This study aimed to investigate the effects of 80 hz vs. 130 Hz frequency STN-DBS on eye movements and executive control. Twenty-one STN-DBS PD patients receiving 130 Hz vs. 80 Hz stimulation were compared to a healthy control group (n = 16). All participants were tested twice in a double-blind manner. We examined prosaccades (latency and gain) and antisaccades (latency of correct and incorrect antisaccades, error rate and gain of the correct antisaccades). Executive function was tested with the Stroop task. The motor condition was assessed using Unified Parkinson's Disease Rating Scale part III. The antisaccadic error rate was higher in patients (p = 0.0113), more so in patients on 80 Hz compared to 130 Hz (p = 0.001) stimulation. The differences between patients and controls and between frequencies for all other eye-movements or cognitive measures were not statistically significant. We show that 80 Hz STN-DBS in PD reduces the ability to maintain stable fixation but does not alter inhibition, resulting in a higher antisaccade error rate presumably due to less efficient fixation, without altering the motor state. This provides a wider range of stimulation parameters that can reduce specific DBS-related effects without affecting motor outcomes.

Principles of gait encoding in the subthalamic nucleus of people with Parkinson's disease.

Disruption of subthalamic nucleus dynamics in Parkinson's disease leads to impairments during walking. Here, we aimed to uncover the principles through which the subthalamic nucleus encodes functional and dysfunctional walking in people with Parkinson's disease. We conceived a neurorobotic platform embedding an isokinetic dynamometric chair that allowed us to deconstruct key components of walking under well-controlled conditions. We exploited this platform in 18 patients with Parkinson's disease to demonstrate that the subthalamic nucleus encodes the initiation, termination, and amplitude of leg muscle activation. We found that the same fundamental principles determine the encoding of leg muscle synergies during standing and walking. We translated this understanding into a machine learning framework that decoded muscle activation, walking states, locomotor vigor, and freezing of gait. These results expose key principles through which subthalamic nucleus dynamics encode walking, opening the possibility to operate neuroprosthetic systems with these signals to improve walking in people with Parkinson's disease.

Electrophysiological confrontation of Lead-DBS-based electrode localizations in patients with Parkinson's disease undergoing deep brain stimulation.

Microelectrode recordings (MERs) are often used during deep brain stimulation (DBS) surgeries to confirm the position of electrodes in patients with advanced Parkinson's disease. The present study focused on 32 patients who had undergone DBS surgery for advanced Parkinson's disease. The first objective was to confront the anatomical locations of intraoperative individual MERs as determined electrophysiologically with those determined postoperatively by image reconstructions. The second aim was to search for differences in cell characteristics among the three subthalamic nucleus (STN) subdivisions and between the STN and other identified subcortical structures. Using the DISTAL atlas implemented in the Lead-DBS image reconstruction toolbox, each MER location was determined postoperatively and attributed to specific anatomical structures (sensorimotor, associative or limbic STN; substantia nigra [SN], thalamus, nucleus reticularis polaris, zona incerta [ZI]). The STN dorsal borders determined intraoperatively from electrophysiology were then compared with the STN dorsal borders determined by the reconstructed images. Parameters of spike clusters (firing rates, amplitudes - with minimum amplitude of 60 µV -, spike durations, amplitude spectral density of ß-oscillations) were compared between structures (ANOVAs on ranks). Two hundred and thirty one MERs were analyzed (144 in 34 STNs, 7 in 4 thalami, 5 in 4 ZIs, 34 in 10 SNs, 41 others). The average difference in depth of the electrophysiological dorsal STN entry in comparison with the STN entry obtained with Lead-DBS was found to be of 0.1 mm (standard deviation: 0.8 mm). All 12 analyzed MERs recorded above the electrophysiologically-determined STN entry were confirmed to be in the thalamus or zona incerta. All MERs electrophysiologically attributed to the SN were confirmed to belong to this nucleus. However, 6/34 MERs that were electrophysiologically attributed to the ventral STN were postoperatively reattributed to the SN. Furthermore, 44 MERs of 3 trajectories, which were intraoperatively attributed to the STN, were postoperatively reattributed to the pallidum or thalamus. MER parameters seemed to differ across the STN, with higher spike amplitudes (H = 10.64, p < 0.01) and less prevalent ß-oscillations (H = 9.81, p < 0.01) in the limbic STN than in the sensorimotor and associative subdivisions. Some cells, especially in the SN, showed longer spikes with lower firing rates, in agreement with described characteristics of dopamine cells. However, these probabilistic electrophysiological signatures might become clinically less relevant with the development of image reconstruction tools, which deserve to be applied intraoperatively.

Modeling of Electric Fields in Individual Imaging Atlas for Capsular Threshold Prediction of Deep Brain Stimulation in Parkinson's Disease: A Pilot Study.

Background: Modeling of deep brain stimulation electric fields and anatomy-based software might improve post-operative management of patients with Parkinson's disease (PD) who have benefitted from subthalamic nucleus deep brain stimulation (STN-DBS). Objective: We compared clinical and software-guided determination of the thresholds for current diffusion to the pyramidal tract, the most frequent limiting side effect in post-operative management of STN-DBS PD patients. Methods: We assessed monopolar reviews in 16 consecutive STN-DBS PD patients and retrospectively compared clinical capsular thresholds, which had been assessed according to standard clinical practice, to those predicted by volume of tissue activated (VTA) model software. All the modeling steps were performed blinded from patients' clinical evaluations. Results: At the group level, we found a significant correlation (p = 0.0001) when performing statistical analysis on the z-scored capsular thresholds, but with a low regression coefficient (r = 0.2445). When considering intra-patient analysis, we found significant correlations (p < 0.05) between capsular threshold as modeled with the software and capsular threshold as determined clinically in five patients (31.2%). Conclusions: In this pilot study, the VTA model software was of limited assistance in identifying capsular thresholds for the whole cohort due to a large inter-patient variability. Clinical testing remains the gold standard in selecting stimulation parameters for STN-DBS in PD.

Complex movement disorder in a patient with heterozygous YY1 mutation (Gabriele-de Vries syndrome).

YY1 mutations cause Gabriele-de Vries syndrome, a recently described condition involving cognitive impairment, facial dysmorphism and intrauterine growth restriction. Movement disorders were reported in 5/10 cases of the original series, but no detailed description was provided. Here we present a 21-year-old woman with a mild intellectual deficit, facial dysmorphism and a complex movement disorder including an action tremor, cerebellar ataxia, dystonia, and partial ocular apraxia as the presenting and most striking feature. Whole-exome sequencing revealed a novel heterozygous de novo mutation in YY1 [NM: 003403.4 (YY1): c.907 T > C; p.(Cys303Arg)], classified as pathogenic according to the ACMG guidelines.

Dyskinesia-inducing lead contacts optimize outcome of subthalamic stimulation in Parkinson's disease.

BACKGROUND: Acute dyskinesias elicited by STN-DBS, here referred to as stimulation-induced dyskinesias, predict optimal clinical outcome in PD. However, it remains elusive whether stimulation-induced dyskinesias can guide DBS programming. OBJECTIVES: Here, we characterized stimulation-induced dyskinesias clinically and anatomically. We then tested whether dyskinesia-inducing contacts could be effectively programmed using independent current source technology. METHODS: We characterized stimulation-induced dyskinesias with directional and ring stimulation retrospectively in 20 patients. We then localized dyskinesia-inducing contacts by imaging coregistration and eventually programmed those contacts. RESULTS: We elicited dyskinesias in half of our patients. Dyskinesia-inducing contacts were mainly directional and were all located ventrally within the dorsolateral motor STN. When these dyskinesia-inducing contacts were programmed using independent current source technology, dyskinesia disappeared and robust antibradykinetic effects were obtained. CONCLUSION: We confirm that stimulation-induced dyskinesias are helpful clinical observations, which may guide programming of directional STN-DBS in PD. © 2019 International Parkinson and Movement Disorder Society.

Effect of Low versus High Frequency Subthalamic Deep Brain Stimulation on Speech Intelligibility and Verbal Fluency in Parkinson's Disease: A Double-Blind Study.

BACKGROUND: Subthalamic deep brain stimulation (STN-DBS) is an established treatment for late stage Parkinson's disease (PD). Speech intelligibility (SI) and verbal fluency (VF) have been shown to deteriorate following chronic STN-DBS. It has been suggested that speech might respond favourably to low frequency stimulation (LFS). OBJECTIVE: We examined how SI, perceptual speech characteristics, phonemic and semantic VF and processes underlying it (clustering and switching) respond to LFS of 60 and 80 Hz in comparison to high frequency stimulation (HFS) (110, 130 and 200 Hz). METHODS: In this double-blind study, 15 STN-DBS PD patients (mean age 65, SD = 5.8, 14 right handed, three females), were assessed at five stimulation frequencies: 60 Hz, 80 Hz, 110 Hz, 130 Hz and 200 Hz. In addition to the clinical neurological assessment of speech, VF and SI were assessed. RESULTS: SI and in particular articulation, respiration, phonation and prosody improved with LFS (all p < 0.05). Phonemic VF switching improved with LFS (p = 0.005) but this did not translate to an improved phonemic VF score. A trend for improved semantic VF was found. A negative correlation was found between perceptual characteristics of speech and duration of chronic stimulation (all p < 0.05). CONCLUSIONS: These findings highlight the need for meticulous programming of frequency to maximise SI in chronic STN-DBS. The findings further implicate stimulation frequency in changes to specific processes underlying VF, namely phonemic switching and demonstrate the potential to address such deficits through advanced adjustment of stimulation parameters.

Impact of Subthalamic Deep Brain Stimulation Frequency on Upper Limb Motor Function in Parkinson's Disease.

BACKGROUND: Whilst changes in the frequency of subthalamic deep brain stimulation (STN-DBS) have been proposed to improve control of tremor or axial motor features in Parkinson's disease (PD), little is known about the effects of frequency changes on upper limb motor function, particularly bradykinesia. OBJECTIVE: To investigate the acute effects of various STN-DBS frequencies (40-160 Hz, 40 Hz intervals) on upper limb motor function. METHODS: We carried out a randomised, double-blind study on 20 PD patients with chronic STN-DBS using the Simple and Assembly components of the Purdue Pegboard (PP) test and a modified upper limb version of the UPDRS-III (UL-UPDRS-III). RESULTS: There was no significant effect of frequency on bradykinesia on the Simple PP task or the UL-UPDRS-III. There was an effect of frequency on the Assembly PP score when comparing all frequencies (p = 0.019) and between 80 Hz and 130 Hz (p = 0.007), with lower frequencies yielding a better performance. Rigidity and Tremor scores were significantly reduced with higher (>80 Hz) compared to lower (40 Hz) frequencies. CONCLUSIONS: Our findings suggest that a wide range of frequencies are efficacious in improving acute upper-limb motor function. Reducing the frequency of stimulation down to 80 Hz is safe and has a similar clinical effect to higher frequencies. Therefore, a wider range of frequencies are available when it comes adjusting patients' acute settings without the risk of worsening bradykinesia.

[Advanced Parkinson's disease : indication for complex treatments]. / Maladie de Parkinson au stade avancé : indication aux traitements complexes.

Advanced Parkinson's disease (PD) is characterized by severe motor and non-motor complications that negatively impact on patients' autonomy and health-related quality of life. In early disease, the therapeutic strategy consists of gradual increase in dopaminergic treatment and levodopa dose fragmentation. In more advanced stages, this approach becomes insufficient and three therapeutic options can be considered: deep brain stimulation (DBS), continuous subcutaneous apomorphine infusion, and continuous levodopa/carbidopa intestinal gel infusion.

La maladie de Parkinson (MP) avancée est caractérisée par la présence de complications motrices et non motrices qui ont un impact significatif sur l'autonomie et la qualité de vie des patients. La stratégie thérapeutique consiste à fractionner le traitement dopaminergique, à recourir aux formes à libération prolongée, et aux inhibiteurs des enzymes de dégradation de la dopamine. Lorsque ces mesures sont insuffisantes, trois options thérapeutiques plus invasives peuvent être envisagées : la stimulation cérébrale profonde, la perfusion sous-cutanée continue d'apomorphine et l'administration intrajéjunale de gel de lévodopa/carbidopa. L'objectif de cet article est de décrire les indications, bénéfices et effets secondaires potentiels de ces traitements dits « complexes ¼.

[Movement disorders emergencies]. / Mouvements anormaux aux urgences.

Unlike most basal ganglia disorders, which usually progress slowly and relentlessly, a number of movement disorders may develop as acute or subacute conditions. Their occurrence commonly prompts patients to rush into the emergency room. A proper diagnosis is not always straightforward and requires a detailed analysis of the movement disorder phenomenology and a thorough medication screening, as many of these acute situations may be iatrogenic and drug-related. An accurate identification of the problem may enable an effective management and an appropriate therapy. This article is an overview of three distinct movement disorder emergencies, namely acute dystonia, acute chorea, and acute complications that can be observed in Parkinson's disease. Each topic is illustrated with a case report.

Contrairement à la plupart des affections des ganglions de la base, qui évoluent généralement sur un mode lentement progressif, certains mouvements anormaux peuvent se développer sur un mode aigu ou subaigu, amenant les patients à consulter en urgence. Le diagnostic est souvent délicat. Il repose sur une analyse détaillée de la phénoménologie et une anamnèse médicamenteuse fouillée, dans la mesure où ces situations sont volontiers iatrogènes. Une identification correcte du problème permet souvent une thérapeutique efficace. Le présent article propose une mise au point de trois problématiques de ce type, à savoir la dystonie aiguë, la chorée aiguë et les complications aiguës que l'on peut observer dans la maladie de Parkinson. Chaque sujet est illustré par un cas clinique.

Short pulse width in subthalamic stimulation in Parkinson's disease: a randomized, double-blind study.

BACKGROUND: We investigated the acute effect of short pulse widths on the therapeutic window in subthalamic nucleus deep brain stimulation in Parkinson's disease. METHODS: We assessed 10 PD patients with STN-DBS at a 60-µs pulse width. We randomly and double-blindedly applied 10- to 50-µs pulse widths. The principal outcome was the therapeutic window (difference between the amplitude thresholds for visible muscle contraction and for best rigidity control). The secondary outcome was the charge per pulse (which reflects the efficiency of the stimulation) needed to control rigidity. Two-way analysis of variance and pairwise t tests were applied. RESULTS: The therapeutic window widened when the pulse width shortened (r = -0.45; P < 0.001), and charge per pulse was reduced (P < 0.05). CONCLUSIONS: This randomized, double-blind study showed that shorter pulse widths widen the therapeutic window of STN-DBS in PD without increasing the electrical charge required to obtain the same acute clinical benefit. © 2017 International Parkinson and Movement Disorder Society.

tDCS changes in motor excitability are specific to orientation of current flow.

BACKGROUND: Measurements and models of current flow in the brain during transcranial Direct Current Stimulation (tDCS) indicate stimulation of regions in-between electrodes. Moreover, the folded cortex results in local fluctuations in current flow intensity and direction, and animal studies suggest current flow direction relative to cortical columns determines response to tDCS. METHODS: Here we test this idea by using Transcranial Magnetic Stimulation Motor Evoked Potentials (TMS-MEP) to measure changes in corticospinal excitability following tDCS applied with electrodes aligned orthogonal (across) or parallel to M1 in the central sulcus. RESULTS: Current flow models predicted that the orthogonal electrode montage produces consistently oriented current across the hand region of M1 that flows along cortical columns, while the parallel electrode montage produces non-uniform current directions across the M1 cortical surface. We find that orthogonal, but not parallel, orientated tDCS modulates TMS-MEPs. We also show modulation is sensitive to the orientation of the TMS coil (PA or AP), which is thought to select different afferent pathways to M1. CONCLUSIONS: Our results are consistent with tDCS producing directionally specific neuromodulation in brain regions in-between electrodes, but shows nuanced changes in excitability that are presumably current direction relative to column and axon pathway specific. We suggest that the direction of current flow through cortical target regions should be considered for targeting and dose-control of tDCS.

Pyramidal tract activation due to subthalamic deep brain stimulation in Parkinson's disease.

BACKGROUND: Subthalamic deep brain stimulation (STN-DBS) is an effective treatment for Parkinson's disease (PD), but can have side effects caused by stimulus spread to structures outside the target volume such as the pyramidal tract. OBJECTIVES: To assess the relevance of pyramidal tract activation with STN-DBS in PD. METHODS: In a multimodal, blinded study in 20 STN-DBS patients, we measured stimulation thresholds for evoking electromyographic activity in orbicularis oris and first dorsal interosseous muscles at each of 150 electrode sites. We also modeled the electric field spread and calculated its overlap with the estimated anatomical location of corticospinal and corticobulbar tracts from primary motor cortex using 3 Tesla MRI probabilistic tractography. RESULTS: Mean resting motor thresholds were significantly lower for the contralateral orbicularis oris (3.5 ± 1.0 mA) compared with ipsilaterally (4.1 ± 1.1 mA) and with the contralateral first dorsal interosseous (4.0 ± 1.2 mA). The modeled volumes of corticobulbar and corticospinal tract activated correlated inversely with the resting motor threshold of the contralateral orbicularis oris and first dorsal interosseous, respectively. Active motor thresholds were significantly lower compared with resting motor thresholds by around 30% to 35% and correlated with the clinically used stimulation amplitude. Backward multiple regression in 12 individuals with a "lateral-type" speech showed that stimulation amplitude, levodopa equivalent dose reduction postsurgery, preoperative speech intelligibility, and first dorsal interosseous resting motor thresholds explained 79.9% of the variance in postoperative speech intelligibility. CONCLUSIONS: Direct pyramidal tract activation can occur at stimulation thresholds that are within the range used in clinical routine. This spread of current compromises increase in stimulation strengths and is related to the development of side effects such as speech disturbances with chronic stimulation. © 2017 International Parkinson and Movement Disorder Society.

[Trajectory of a patient with deep brain stimulation (DBS)]. / Stimulation cérébrale profonde: trajectoire du patient.

An eligibility assessment for deep brain stimulation is performed in order to select patients who are likely to benefit from it. Parkinson's patients have to stop dopaminergic drugs the day before surgery. During the operation, the patient must remain awake for recording of neuronal activity and for test stimulations to optimize the position of the electrodes. Postoperatively, the stimulation is increased progressively in parallel with a decrease of dopaminergic treatments. After about ten days, the patient can return to home and controls continue as an outpatient. Three months postoperatively, a complete testing of the neurostimulator is performed and at the one year follow-up visit, the effectiveness of the DBS is assessed.

Sleep apnea syndrome: improved detection of respiratory events and cortical arousals using oxymetry pulse wave amplitude during polysomnography.

Respiratory events (RE) during sleep induce cortical arousals (A) and marked changes in autonomic markers in sleep apnea syndrome (SAS). The aims of the study were double. First, we assessed whether pulse wave amplitude (PWA) added to polysomnography (PSG) could improve RE and A detection; second, we wanted to know whether the quality of detection of these two parameters could be improved using PWA. Respiratory disturbance index (RDI) and A were randomly scored twice by the same observer in 12 male patients with SAS. The first scoring was done using conventional PSG signals, the second scoring adding PWA to PSG. We also measured interobserver agreement by randomly selecting and reading 100 PSG sequences of 5 min with and without PWA by two observers. Adding PWA to PSG parameters allowed to detect significantly more RDI (53.9 +/- 21.6 h(-1) versus 48.3 +/- 22.3 h(-1), p < 0.001) and more A (68.0 +/- 14.4 versus 59.4 +/- 16.5, p < 0.001). Moreover, after using PWA, there was no significant disagreement between two observers for detecting RE, showing better quality of RE detection. PWA is a simple and cheap parameter that improves the diagnostic value of conventional PSG in sleep apnea syndrome by better detecting respiratory events and A.