A comparison of methods to suppress electrocardiographic artifacts in local field potential recordings

OBJECTIVE

Local field potential (LFP) recordings from deep brain stimulation (DBS) electrodes are often contaminated with electrocardiographic (ECG) artifacts that hinder the detection of disease-specific electrical brain activity.

METHODS

Three ECG suppression methods were evaluated: (1) QRS interpolation of the Perceive toolbox, (2) template subtraction, and (3) singular value decomposition (SVD). LFPs were recorded with the Medtronic Percept^TM PC system in nine Parkinson's disease patients with stimulation OFF ("OFF-DBS"; anode disconnected) and ON at 0 mA ("ON-DBS 0 mA"; anode connected). Findings were verified with simulated ECG-contaminated time series.

RESULTS

ECG artifacts were present in 10 out of 18 ON-DBS 0 mA recordings. All ECG suppression methods drastically reduced artifact-induced beta band (13-35 Hz) power and at least partly recovered the beta peak and beta burst dynamics. Using external ECG recordings and lengthening artifact epoch length improved the performance of the suppression methods. Increasing epoch length, however, elevated the risk of flattening the beta peak and losing beta burst dynamics.

CONCLUSIONS

The SVD method formed the preferred trade-off between artifact cleaning and signal loss, as long as its parameter settings are adequately chosen.

SIGNIFICANCE

ECG suppression methods enable analysis of disease-specific neural activity from signals affected by ECG artifacts.

Elective and Emergency Deep Brain Stimulation in Refractory Pediatric Monogenetic Movement Disorders Presenting with Dystonia: Current Practice Illustrated by Two Cases

BACKGROUND

Dystonia is characterized by sustained or intermittent muscle contractions, leading to abnormal posturing and twisting movements. In pediatric patients, dystonia often negatively influences quality of life. Pharmacological treatment for dystonia is often inadequate and causes adverse effects. Deep brain stimulation (DBS) appears to be a valid therapeutic option for pharmacoresistant dystonia in children.

METHODS

To illustrate the current clinical practice, we hereby describe two pediatric cases of monogenetic movement disorders presenting with dystonia and treated with DBS. We provide a literature review of similar previously described cases and on different clinical aspects of DBS in pediatric dystonia.

RESULTS

The first patient, a 6-year-old girl with severe dystonia, chorea, and myoclonus due to an ADCY5 gene mutation, received DBS in an elective setting. The second patient, an 8-year-old boy with GNAO1-related dystonia and chorea, underwent emergency DBS due to a pharmacoresistant status dystonicus. A significant amelioration of motor symptoms (65% on the Burke-Fahn-Marsden Dystonia Rating Scale) was observed postoperatively in the first patient and her personal therapeutic goals were achieved. DBS was previously reported in five patients with ADCY5-related movement disorders, of which three showed objective improvement. Emergency DBS in our second patient resulted in the successful termination of his GNAO1-related status dystonicus, this being the eighth case reported in the literature.

CONCLUSION

DBS can be effective in monogenetic pediatric dystonia and should be considered early in the disease course. To better evaluate the effects of DBS on patients' functioning, patient-centered therapeutic goals should be discussed in a multidisciplinary approach.

A Clinical Applicable Smartwatch Application for Measuring Hyperkinetic Movement Disorder Severity

Measuring the severity of hyperkinetic movement disorders like tremor and myoclonus is challenging. Although many accelerometers are available to quantify movements, the vast majority lacks real-time analysis and an interface that makes it possible to real-time adjust therapy like deep brain stimulation (DBS). Here, we developed a smartwatch/smartphone application that is capable of real-time analysing movement disorder severity. Movement analysis was realised by integrating acceleration values, to velocity and subsequently to distance. Measured distances were compared with a validated accelerometer already applied for quantifying movement disorders. Further validation was done by quantitative assessment of simulated movement disorders in 10 healthy volunteers. Finally, the approach was tested in two patients treated with DBS to quantify the effect of different DBS settings on myoclonus and tremor severity, respectively. The distance measured with the application had a 96% accuracy. This was non-inferior (p = 0.76) compared to accelerometers already clinically applied. Furthermore, (simulated) movement disorder severity could be classified correctly in 93% of the cases. Finally, the method was capable of distinguishing effective from non-effective DBS parameters in two patients. In summary, with our approach we realised an instantaneous and reliable estimation of the severity of movement disorders which can assist in real time titrating therapy like DBS.

Intermuscular coherence as biomarker for pallidal deep brain stimulation efficacy in dystonia

OBJECTIVE

Finding a non-invasive biomarker for Globus Pallidus interna Deep Brain Stimulation (GPi-DBS) efficacy. Dystonia heterogeneity leads to a wide variety of clinical response to GPi-DBS, making it hard to predict GPi-DBS efficacy for individual patients.

METHODS

EEG-EMG recordings of twelve dystonia patients who received bilateral GPi-DBS took place pre- and 1 year post-surgery ON and OFF stimulation, during a rest, pinch, and flexion task. Dystonia severity was assessed using the BFMDRS and TWSTRS (pre- and post-surgery ON stimulation). Intermuscular coherence (IMC) and motorcortex corticomuscular coherence (CMC) were calculated. Low frequency (4-12 Hz) and beta band (13-30 Hz) peak coherences were studied.

RESULTS

Dystonia severity improved after 1 year GPi-DBS therapy (BFMDRS: 30%, median 7.8 (IQR 3-10), TWSTRS: 22%, median 6.8 (IQR 4-9)). 86% of IMC were above the 95% confidence limit. The highest IMC peak decreased significantly with GPi-DBS in the low frequency and beta band. Low frequency and beta band IMC correlated partly with dystonia severity and severity improvement. CMC generally were below the 95% confidence limit.

CONCLUSIONS

Peak low frequency IMC functioned as biomarker for GPi-DBS efficacy, and partly correlated with dystonia severity.

SIGNIFICANCE

IMC can function as biomarker. Confirmation in a larger study is needed for use in clinical practice.

Improving neurophysiological biomarkers for functional myoclonic movements

Introduction

Differentiating between functional jerks (FJ) and organic myoclonus can be challenging. At present, the only advanced diagnostic biomarker to support FJ is the Bereitschaftspotential (BP). However, its sensitivity is limited and its evaluation subjective. Recently, event related desynchronisation in the broad beta range (13–45 Hz) prior to functional generalised axial (propriospinal) myoclonus was reported as a possible complementary diagnostic marker for FJ. Here we study the value of ERD together with a quantified BP in clinical practice.

Methods

Twenty-nine patients with FJ and 16 patients with cortical myoclonus (CM) were included. Jerk-locked back-averaging for determination of the ‘classical’ and quantified BP, and time-frequency decomposition for the event related desynchronisation (ERD) were performed. Diagnostic gain, sensitivity and specificity were obtained for individual and combined techniques.

Results

We detected a classical BP in 14/29, a quantitative BP in 15/29 and an ERD in 18/29 patients. At group level we demonstrate that ERD in the broad beta band preceding a jerk has significantly higher amplitude in FJ compared to CM (respectively −0.14 ± 0.13 and +0.04 ± 0.09 (p < 0.001)). Adding ERD to the classical BP achieved an additional diagnostic gain of 53%. Furthermore, when combining ERD with quantified and classical BP, an additional diagnostic gain of 71% was achieved without loss of specificity.

Conclusion

Based on the current findings we propose to the use of combined beta ERD assessment and quantitative BP analyses in patients with a clinical suspicion for all types of FJ with a negative classical BP.

•

Differentiating between functional jerks and organic myoclonus is often difficult.

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The sensitivity of a positive bereitschaftspotential for diagnosing FJ is low.

•

FJ are preceded by event related desynchronisation (ERD) in the beta band.

•

Combining beta ERD and BP improves diagnosing FJ.

•

The ERD method is of special relevance in possible FJ patients with a negative BP.

Hippocampus activation related to 'real-time' processing of visuospatial change

The delay associated with cerebral processing time implies a lack of real-time representation of changes in the observed environment. To bridge this gap for motor actions in a dynamical environment, the brain uses predictions of the most plausible future reality based on previously provided information. To optimise these predictions, adjustments to actual experiences are necessary. This requires a perceptual memory buffer. In our study we gained more insight how the brain treats (real-time) information by comparing cerebral activations related to judging past-, present- and future locations of a moving ball, respectively. Eighteen healthy subjects made these estimations while fMRI data was obtained. All three conditions evoked bilateral dorsal-parietal and premotor activations, while judgment of the location of the ball at the moment of judgment showed increased bilateral posterior hippocampus activation relative to making both future and past judgments at the one-second time-sale. Since the condition of such 'real-time' judgments implied undistracted observation of the ball's actual movements, the associated hippocampal activation is consistent with the concept that the hippocampus participates in a top-down exerted sensory gating mechanism. In this way, it may play a role in novelty (saliency) detection.

Adaptive deep brain stimulation in Parkinson's disease

Although Deep Brain Stimulation (DBS) is an established treatment for Parkinson's disease (PD), there are still limitations in terms of effectivity, side-effects and battery consumption. One of the reasons for this may be that not only pathological but also physiological neural activity can be suppressed whilst stimulating. For this reason, adaptive DBS (aDBS), where stimulation is applied according to the level of pathological activity, might be advantageous. Initial studies of aDBS demonstrate effectiveness in PD, but there are still many questions to be answered before aDBS can be applied clinically. Here we discuss the feedback signals and stimulation algorithms involved in adaptive stimulation in PD and sketch a potential road-map towards clinical application.

Electroencephalographic Findings in Posthypoxic Myoclonus

The physical examination findings of early posthypoxic myoclonus (PHM) are associated with poor prognosis. Recent findings indicate that patients with multifocal PHM, assumed to have a cortical origin, have a comparable outcome to resuscitated patients without PHM. Generalized PHM, assumed to have a subcortical myoclonus origin, is still associated with a bad clinical outcome. It is not known whether the electroencephalographic (EEG) findings differ between the multifocal and generalized myoclonus groups nor is the clinical significance clearly defined. Forty-three patients with PHM were retrospectively derived from an EEG database. Patients were categorized as having multifocal (i), generalized (ii), or undetermined (iii) PHM. Outcome was expressed in cerebral performance category scores. The EEG background was categorized into isoelectric (I), low voltage (II), burst suppression (III), status epilepticus (SE; IV), diffuse slowing (V), and mild encephalopathic or normal (VI). 17 patients had generalized PHM and 23 had multifocal PHM (3 undetermined). The EEG showed more SE in generalized compared to multifocal PHM (64% vs 13%, P< .001). Diffuse slowing was more often present in multifocal PHM (52% vs 17%, P < .05). Early-onset myoclonus occurred significantly more often in generalized PHM, and early generalized PHM was invariantly associated with poor outcome. In conclusion, patients with generalized PHM showed more SE. These EEG findings might be either subcortical corollaries or primarily cortical phenomena. Our retrospective results conflict with currently used clinical criteria for myoclonus classification, and we suggest that more refined difference may be needed for accurate assessment of PHM. To better understand PHM, prospective research with standardized clinical assessment and quantitative EEG analysis is needed.

Secondary sensory area SII is crucially involved in the preparation of familiar movements compared to movements never made before

Secondary sensorimotor regions are involved in sensorimotor integration and movement preparation. These regions take part in parietal-premotor circuitry that is not only active during motor execution but also during movement observation and imagery. This activation particularly occurs when observed movements belong to one's own motor repertoire, consistent with the finding that motor imagery only improves performance when one can actually make such movement. We aimed to investigate whether imagery or observation of a movement that was never made before causes parietal-premotor activation or that the ability to perform this movement is indeed a precondition. Nine subjects [group Already Knowing It (AKI)] could abduct their hallux (moving big toe outward). Seven subjects initially failed to make such movement (Absolute Zero A0 group). They had to imagine, observe, or execute this movement, whereas fMRI data were obtained both before and after training. Contrasting abduction observation between the AKI-group and A0-group showed increased left SII and supplementary motor area activation. Comparing the observation of hallux flexion with abduction showed increased bilateral SII activation in the A0 and not in the AKI group. Prolonged training resulted in equal performance and similar cerebral activation patterns in the two groups. Thereby, conjunction analysis of the correlations on subject's range of abduction during execution, imagery, and observation of hallux abduction showed exclusive bilateral SII activation. The reduced SII involvement in A0 may imply that effective interplay between sensory predictions and feedback does not take place without actual movement experience. However, this can be acquired by training.

Interruption of visually perceived forward motion in depth evokes a cortical activation shift from spatial to intentional motor regions

Forward locomotion generates a radially expanding flow of visual motion which supports goal-directed walking. In stationary mode, wide-field visual presentation of optic flow stimuli evokes the illusion of forward self-motion. These effects illustrate an intimate relation between visual and motor processing. In the present fMRI study, we applied optic flow to identify distinct interfaces between circuitries implicated in vision and movement. The dorsal premotor cortex (PMd) was expected to contribute to wide-field forward motion flow (FFw), reflecting a pathway for externally triggered motor control. Medial prefrontal activation was expected to follow interrupted optic flow urging internally generated action. Data of 15 healthy subjects were analyzed with Statistical Parametric Mapping and confirmed this hypothesis. Right PMd activation was seen in FFw, together with activations of posterior parietal cortex, ventral V5, and the right fusiform gyrus. Conjunction analysis of the transition from wide to narrow forward flow and reversed wide-field flow revealed selective dorsal medial prefrontal activation. These findings point at equivalent visuomotor transformations in locomotion and goal-directed hand movement, in which parietal-premotor circuitry is crucially implicated. Possible implications of an activation shift from spatial to intentional motor regions for understanding freezing of gait in Parkinson's disease are discussed: impaired medial prefrontal function in Parkinson's disease may reflect an insufficient internal motor drive when visual support from optic flow is reduced at the entrance of a narrow corridor.

Cerebral representations of space and time

A link between perception of time and spatial change is particularly revealed in dynamic conditions. By fMRI, we identified regional segregation as well as overlap in activations related to spatial and temporal processing. Using spatial and temporal anticipation concerning movements of a ball provided a balanced paradigm for contrasting spatial and temporal conditions. In addition, momentary judgments were assessed. Subjects watched a monitor-display with a moving ball that repeatedly disappeared. Ordered in 4 conditions, they indicated either where or when the ball would hit the screen bottom, where it actually disappeared or what its speed was. Analysis with SPM showed posterior parietal activations related to both spatial- and temporal predictions. After directly contrasting these two conditions, parietal activations remained robust in spatial prediction but virtually disappeared in temporal prediction, while additional left cerebellar-right prefrontal and pre-SMA activations in temporal prediction remained unchanged. Speed contrasted to the location of disappearance showed similar parietal decrease with maintained cerebellar-prefrontal activations, but also increased caudate activation. From these results we inferred that parietal-based spatial information was a prerequisite for temporal processing, while prefrontal-cerebellar activations subsequently reflected working memory and feedforward processing for the assessment of differences between past and future spatial states. We propose that a temporal component was extracted from speed, i.e. approximated momentary time, which demarcated minimal intervals of spatial change (defined by neuronal processing time). The caudate association with such interval demarcation provided an argument to integrate concepts of space-referenced time processing and a clock-like processing model.