Abnormal contingent negative variation in writer's cramp

Contemporary clinical neurophysiology applications in dystonia

The complex phenomenological understanding of dystonia has transcended from the clinics to genetics, imaging and neurophysiology. One way in which electrophysiology will impact into the clinics are cases wherein a dystonic clinical presentation may not be typical or a "forme fruste" of the disorder. Indeed, the physiological imprints of dystonia are present regardless of its clinical manifestation. Underpinnings in the understanding of dystonia span from the peripheral, segmental and suprasegmental levels to the cortex, and various electrophysiological tests have been applied in the course of time to elucidate the origin of dystonia pathophysiology. While loss of inhibition remains to be the key finding in this regard, intricacies and variabilities exist, thus leading to a notion that perhaps dystonia should best be gleaned as network disorder. Interestingly, the complex process has now spanned towards the understanding in terms of networks related to the cerebellar circuitry and the neuroplasticity. What is evolving towards a better and cohesive view will be neurophysiology attributes combined with structural dynamic imaging. Such a sound approach will significantly lead to better therapeutic modalities in the future.

Sensory tricks in cervical dystonia correlate with enhanced brain activity during motor preparation

INTRODUCTION

Although sensory tricks are well known as the maneuvers that temporarily relieve dystonic symptoms in patients with cervical dystonia (CD), the underlying neurophysiological mechanisms remain unclear. We aimed to investigate brain potentials related to sensory tricks in patients with CD.

METHODS

Thirteen patients with CD and 13 age-matched healthy volunteers participated. The experiment consisted of three conditions (moving the neck, moving an arm, and performing sensory tricks) presented in different blocks in random order in a contingent negative variation (CNV) paradigm. Warning and trigger stimuli (S1 and S2) were presented to the participants, who were instructed to prepare to perform the specific task for each condition after S1, and then to perform the task after S2. Early and late components of the CNV were measured.

RESULTS

The late CNVs in patients with CD were significantly larger than those in healthy participants in Fz, FCz, Cz, and C3 electrodes. Only in patients with CD, the late CNVs were significantly greater for the 'sensory tricks' condition compared to the 'move neck' condition in Fz and C3 electrodes.

CONCLUSION

The late CNV is increased during sensory tricks in patients with CD, suggesting that sensory tricks may affect mechanisms related to the motor preparatory phase in the premotor and primary motor areas. Sensory tricks may normalize impaired motor preparation in dystonia, leading to improved dystonic symptoms.

Pearls and pitfalls in brain functional analysis by event-related potentials: a narrative review by the Italian Psychophysiology and Cognitive Neuroscience Society on methodological limits and clinical reliability-part I

Event-related potentials (ERPs) are obtained from the electroencephalogram (EEG) or the magnetoencephalogram (MEG, event-related fields (ERF)), extracting the activity that is time-locked to an event. Despite the potential utility of ERP/ERF in cognitive domain, the clinical standardization of their use is presently undefined for most of procedures. The aim of the present review is to establish limits and reliability of ERP medical application, summarize main methodological issues, and present evidence of clinical application and future improvement. The present section of the review focuses on well-standardized ERP methods, including P300, Contingent Negative Variation (CNV), Mismatch Negativity (MMN), and N400, with a chapter dedicated to laser-evoked potentials (LEPs). One section is dedicated to proactive preparatory brain activity as the Bereitschaftspotential and the prefrontal negativity (BP and pN). The P300 and the MMN potentials have a limited but recognized role in the diagnosis of cognitive impairment and consciousness disorders. LEPs have a well-documented usefulness in the diagnosis of neuropathic pain, with low application in clinical assessment of psychophysiological basis of pain. The other ERP components mentioned here, though largely applied in normal and pathological cases and well standardized, are still confined to the research field. CNV, BP, and pN deserve to be largely tested in movement disorders, just to explain possible functional changes in motor preparation circuits subtending different clinical pictures and responses to treatments.

Contingent negative variation: a biomarker of abnormal attention in functional movement disorders

BACKGROUND AND PURPOSE

Contingent negative variation (CNV) is a negative cortical wave that precedes a pre-cued imperative stimulus requiring a quick motor response. It has been related to motor preparation and anticipatory attention. The aim was to ascertain whether the clinical improvement of functional movement disorders after physiotherapy would be associated with faster reaction times and modulation of CNV.

METHODS

Motor performance and CNV were analysed during a pre-cued choice reaction time task with varying cue validity. Twenty-one patients with functional movement disorders and 13 healthy controls at baseline were compared. Patients then underwent physiotherapy. At follow-up after physiotherapy, patients were categorized as clinically improved (responders) or not improved (non-responders) and retested.

RESULTS

At baseline, patients did not generate CNV, contrary to controls [mean amplitude (µV) at the end of preparation to move: patients -0.47 (95% CI -1.94, 1.00) versus controls -2.59 (95% CI -4.46, -0.72)]. Responders performed faster after physiotherapy [mean natural logarithm (ln) reaction time (RT) (ms): follow-up 6.112 (95% CI 5.923, 6.301) versus baseline 6.206 (95% CI 6.019, 6.394), P = 0.010], contrary to non-responders. Simultaneously, responders showed a recovery of CNV after physiotherapy [follow-up -1.95 (95% CI -3.49, -0.41) versus baseline -0.19 (95% CI -1.73, 1.35), P < 0.001], contrary to non-responders [follow-up -0.32 (95% CI -1.79, 1.14) versus baseline -0.72 (95% CI -2.19, 0.75), P = 0.381].

CONCLUSIONS

Clinical improvement of functional movement disorders after physiotherapy was associated with faster reaction times and normalization of CNV, which was absent at baseline. These findings suggest that CNV may constitute a useful neurophysiological biomarker related to abnormal attention in functional movement disorders.

Network-specific resting-state connectivity changes in the premotor-parietal axis in writer's cramp

Background

Writer's cramp is a task-specific dystonia impairing writing and sometimes other fine motor tasks. Neuroimaging studies using manifold designs have shown varying results regarding the nature of changes in the disease.

Objective

To clarify and extend the knowledge of underlying changes by investigating functional connectivity (FC) in intrinsic connectivity networks with putative sensorimotor function at rest in an increased number of study subjects.

Methods

Resting-state functional magnetic resonance imaging with independent component analysis was performed in 26/27 writer's cramp patients/healthy controls, and FC within and between resting state networks with putative sensorimotor function was compared. Additionally, voxel-based morphometry was carried out on the subjects' structural images.

Results

Patients displayed increased left- and reduced right-hemispheric primary sensorimotor FC in the premotor-parietal network. Mostly bilaterally altered dorsal/ventral premotor FC, as well as altered parietal FC were observed within multiple sensorimotor networks and showed differing network-dependent directionality. Beyond within-network FC changes and reduced right cerebellar grey matter volume in the structural analysis, the positive between-network FC of the cerebellar network and the basal ganglia network was reduced.

Conclusions

Abnormal resting-state FC in multiple networks with putative sensorimotor function may act as basis of preexisting observations made during task-related neuroimaging. Further, altered connectivity between the cerebellar and basal ganglia network underlines the important role of these structures in the disease.

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Investigation of FC changes in various sensorimotor ICNs at rest in writer's cramp.

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We saw multiple, network-specific FC changes in primary/higher sensorimotor cortices.

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This may act as basis of the varying nature of sensorimotor changes during task-fMRI.

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Further, findings supporting disrupted cerebellar-basal ganglia interaction were made.

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An additional morphometric analysis demonstrated structural cerebellar abnormality.

A practical approach to management of focal hand dystonia

Dystonia can be focal, segmental, multifocal, generalized, or hemidystonia. Focal dystonia is localized to a specific part of the body. Overall upper limb is more commonly involved in focal dystonia than lower limb and since it starts from hand, focal hand dystonia (FHD) is a more accepted terminology. Writer's cramp and musician dystonia are commonest types of FHD. Typically this dystonia is task specific, but in some patients this specificity may be lost over a period of time. Segmental or generalized dystonia may also start as FHD, so a detailed clinical assessment is required, which should be supplemented by relevant investigations. Treatment includes oral medications, injection botulinum toxin, neurosurgery including neurostimulation, and rehabilitation. Role of injection botulinum toxin has been extensively studied in writer's cramp patients and found to be effective; however, selection of muscles and techniques of injection are crucial in getting best results.

Reduced motor cortex deactivation in individuals who suffer from writer's cramp

This study investigated the neuromagnetic activities of self-paced finger lifting task and electrical median nerve stimulation in ten writer's cramp patients and fourteen control subjects. The event-related de/synchronizations (ERD/ERS) of beta-band activity levels were evaluated and the somatosensory cortical activity levels were analyzed using equivalent-current dipole modeling. No significant difference between the patients and control subjects was found in the electrical stimulation-induced beta ERS and electrical evoked somatosensory cortical responses. Movement-related beta ERD did not differ between controls and patients. Notably, the amplitude of the beta ERS after termination of finger movement was significantly lower in the patients than in the control subjects. The reduced movement-related beta ERS might reflect an impairment of motor cortex deactivation. In conclusion, a motor dependent dysregulation of the sensorimotor network seems to be involved in the functional impairment of patients with writer's cramp.

Abnormal movement preparation in task-specific focal hand dystonia

Electrophysiological and behavioral studies in primary dystonia suggest abnormalities during movement preparation, but this crucial phase preceding movement onset has not yet been studied specifically with functional magnetic resonance imaging (fMRI). To identify abnormalities in brain activation during movement preparation, we used event-related fMRI to analyze behaviorally unimpaired sequential finger movements in 18 patients with task-specific focal hand dystonia (FHD) and 18 healthy subjects. Patients and controls executed self-initiated or externally cued prelearnt four-digit sequential movements using either right or left hands. In FHD patients, motor performance of the sequential finger task was not associated with task-related dystonic posturing and their activation levels during motor execution were highly comparable with controls. On the other hand reduced activation was observed during movement preparation in the FHD patients in left premotor cortex / precentral gyrus for all conditions, and for self-initiation additionally in supplementary motor area, left mid-insula and anterior putamen, independent of effector side. Findings argue for abnormalities of early stages of motor control in FHD, manifesting during movement preparation. Since deficits map to regions involved in the coding of motor programs, we propose that task-specific dystonia is characterized by abnormalities during recruitment of motor programs: these do not manifest at the behavioral level during simple automated movements, however, errors in motor programs of complex movements established by extensive practice (a core feature of FHD), trigger the inappropriate movement patterns observed in task-specific dystonia.

Debunking the pathophysiological puzzle of dystonia--with special reference to botulinum toxin therapy

New neurophysiological insights into the natural behaviour of dystonia, obtained during the successful botulinum toxin A (BoNT) treatment of the disorder, have urged the inclusion of sensory (and particularly somatosensory) mechanisms into the pathophysiological background of dystonia. Muscle spindles play a pivotal role in the generation of dystonic movements. Abnormal behaviour in the muscle spindles that generates an irregular proprioceptive input via the group-IA afferents may result in abnormal cortical excitability and intracortical inhibition in dystonia. The aim of this article is to support our hypothesis that dystonic movement is at the end of an impaired function of somatosensory pathways and analysers, which, in turn, may be hinged on the abnormality of sensorimotor integration, that is, brain plasticity. BoNT treatment can potentially modulate this plasticity mechanism and is probably the seminal cause of the sustained effect of the subsequent BoNT-treatment sessions and the long-term alleviation of symptoms of dystonia.

Writer's cramp: increased dorsal premotor activity during intended writing

Simple writer's cramp (WC) is a task-specific form of dystonia, characterized by abnormal movements and postures of the hand during writing. It is extremely task-specific, since dystonic symptoms can occur when a patient uses a pencil for writing, but not when it is used for sharpening. Maladaptive plasticity, loss of inhibition, and abnormal sensory processing are important pathophysiological elements of WC. However, it remains unclear how those elements can account for its task-specificity. We used fMRI to isolate cerebral alterations associated with the task-specificity of simple WC. Subjects (13 simple WC patients, 20 matched controls) imagined grasping a pencil to either write with it or sharpen it. On each trial, we manipulated the pencil's position and the number of imagined movements, while monitoring variations in motor output with electromyography. We show that simple WC is characterized by abnormally increased activity in the dorsal premotor cortex (PMd) when imagined actions are specifically related to writing. This cerebral effect was independent from the known deficits in dystonia in generating focal motor output and in processing somatosensory feedback. This abnormal activity of the PMd suggests that the task-specific element of simple WC is primarily due to alterations at the planning level, in the computations that transform a desired action outcome into the motor commands leading to that action. These findings open the way for testing the therapeutic value of interventions that take into account the computational substrate of task-specificity in simple WC, e.g. modulations of PMd activity during the planning phase of writing.

Pathological basal ganglia activity in movement disorders

Our understanding of the pathophysiology of movement disorders and associated changes in basal ganglia activities has significantly changed during the last few decades. This process began with the development of detailed anatomical models of the basal ganglia, followed by studies of basal ganglia activity patterns in animal models of common movement disorders and electrophysiological recordings in movement disorder patients undergoing functional neurosurgical procedures. These investigations first resulted in an appreciation of global activity changes in the basal ganglia in parkinsonism and other disorders, and later in the detailed description of pathological basal ganglia activity patterns, specifically burst patterns and oscillatory synchronous discharge of basal ganglia neurons. In this review, we critically summarize our current knowledge of the pathological discharge patterns of basal ganglia neurons in Parkinson's disease, dystonia, and dyskinesias.

Neurophysiology of dystonia: The role of inhibition

The pathophysiology of dystonia has been best studied in patients with focal hand dystonia. A loss of inhibitory function has been demonstrated at spinal, brainstem and cortical levels. Many cortical circuits seem to be involved. One consequence of the loss of inhibition is a failure of surround inhibition, and this appears to directly lead to overflow and unwanted muscle spasms. There are mild sensory abnormalities and deficits in sensorimotor integration; these also might be explained by a loss of inhibition. Increasing inhibition may be therapeutic. A possible hypothesis is that there is a genetic loss of inhibitory interneurons in dystonia and that this deficit is a substrate on which other factors can act to produce dystonia. This article is part of a Special Issue entitled "Advances in dystonia".

A kinesthetic motor imagery study in patients with writer' cramp

The aim was to determine if patients with writer' cramp (WC) have abnormalities in kinesthetic motor imagery of hand movements. We timed the execution and simulation of a 'finger tap task' and a 'writing task' in 9 patients with simple WC and 9 matched healthy controls. In the 'finger tap task, patients tended to be slower than controls to execute without vision (p=0.190) and to simulate the movements (p=0.094). In the 'writing task', patients were slower than controls to execute writing with vision (p=0.0001) and without vision of the movements (p=0.0001) and to mentally simulate it (p=0.04). Patients were slower to execute writing than to simulate it (p=0.021) In general, there were not significant correlations between times of execution and simulation of both tasks. In conclusion, patients with WC seem to have slowing in the processes of mental simulation of hand movements that is not specific for writing.

Slow pre-movement cortical potentials do not reflect individual response to therapy in writer's cramp

OBJECTIVE

To investigate whether movement-related cortical potentials (MRCP) provide a physiological correlate that indicates the response to treatment in patients with writer's cramp.

METHODS

In 21 patients with writer's cramp, who underwent 4 weeks of limb immobilization followed by re-training for 8 weeks, we recorded MRCPs preceding a self-initiated brisk finger abduction movement. MRCP measurements of pre-movement activity were performed at baseline, after the end of immobilization and four and 8 weeks of re-training. We examined 12 controls, who received no intervention, twice 4 weeks apart.

RESULTS

Patients benefited from the therapeutical intervention (Zeuner et al., 2008). They showed no abnormalities of the MRCPs at baseline. In controls, MRCPs did not significantly change after 4 weeks. In patients, immobilization and re-training had no effect on MRCPs. There was no correlation between the severity of dystonic symptoms or the individual treatment response and MRCPs.

CONCLUSION

MRCPs are stable measures for interventional studies. However, they do not reflect clinical severity of dystonic symptoms or improvement after therapeutic interventions.

SIGNIFICANCE

This is the first study to investigate MRCPs in a large cohort of patients with writer's cramp compared to a control group at different time points. These potentials do not reflect the motor control disorder in patients with writer's cramp.

The pathophysiology of focal hand dystonia

NARRATIVE REVIEW: Focal hand dystonia is a disabling movement disorder, often task specific, that leads to impaired hand use. In addition to a genetic predisposition, environmental risk factors including repetitive use and musculoskeletal constraints are contributory. Although the underlying cause is unknown, recent studies have identified several key mechanisms that may play a part in its genesis. Failure of inhibition, abnormal sensorimotor integration, and maladaptive plasticity seem to be important. Understanding the underlying physiology may lead to the design of novel therapies.

Changes in the relationship between movement velocity and movement distance in primary focal hand dystonia

The authors examined the relationship between movement velocity and distance and the associated muscle activation patterns in 18 individuals with focal hand dystonia (FHD) compared with a control group of 18 individuals with no known neuromuscular condition. Participants performed targeted voluntary wrist and elbow flexion movements as fast as possible across 5 movement distances. Individuals with FHD were slower than controls across all distances, and this difference was accentuated for longer movements. Muscle activation patterns were triphasic in the majority of individuals with FHD, and muscle activation scaled with distance in a similar manner to controls. Cocontraction did not explain movement slowing in individuals with dystonia, but there was a trend toward underactivation of the 1st agonist burst in the dystonic group. The authors concluded that slowness is a consistent feature of voluntary movement in FHD and is present even in the absence of dystonic posturing. Underactivation of the 1st agonist burst appears to be the most likely reason to explain slowing.

Pathophysiology of writer's cramp

Writer's cramp is a task-specific focal hand dystonia. The abnormality of task specificity is a curious one and indicates that we need to learn more about the coupling of motor programs and their effectors. Writer's cramp appears to be triggered by spending much time writing by an individual with a fertile physiological substrate for producing the disorder. The fertile background, which is likely genetic, may be a decrease of inhibition, an increase of plasticity or an impairment in sensory function. Recent pathophysiological findings have implications for new therapies.

Strength deficits in primary focal hand dystonia

Cortical activation is reduced when patients with focal dystonia perform movements that do not induce dystonic posturing. This finding suggests that the cortical drive to muscles may in some circumstances actually be reduced not increased, as suggested by basal ganglia models of dystonia as a hyperkinetic disorder. The purpose of this study was to examine flexor and extensor strength at the wrist (a clinically affected joint) and elbow (a nonclinically affected joint) in 18 patients with primary focal hand dystonia compared to matched control subjects. We measured peak torque from maximum voluntary contractions, and agonist and antagonist muscle activation by means of surface electromyograms. Patients were significantly weaker than controls at both the elbow and wrist joints and in both flexors and extensors compared to controls. Peak elbow flexion torque was, on average, 14.4% lower in the dystonic compared to the control group, elbow extensor peak torque was 28.6% lower, wrist flexor peak torque was 17.4% lower, and wrist extensor peak torque was 20.7% lower. Strength did not differ as a function of clinical severity. Reductions in peak torque were accompanied by reduced agonist activation, although this finding only reached statistical significance at the elbow. The amount of co-contraction of antagonistic muscles was not significantly different between the two groups. These results are discussed in the context of dystonia as a disorder resulting from dysfunction of basal ganglia output.

Enhanced P1-N1 Auditory Evoked Potential in Patients with Musicians' Cramp

Auditory evoked potentials (AEPs) were examined in patients with musician's cramp (focal dystonia) in order to determine whether these patients have electrophysiological changes in a sensory system that is not usually associated with symptoms. All participants were professional guitarists and were required to listen to 2,000 monaurally presented stimuli (middle C, with duration of 7 ms). During one block, 250 stimuli were presented to one ear. Once a block was finished, another block was presented in the other ear; in total there were eight blocks of stimuli. During this task, EEGs from 10 scalp electrodes and one bipolar eye channel were continuously recorded. There were no significant latency or topographical differences in the electrophysiological recordings. However, there was a significant group difference in the peak-to-peak amplitude of the P1-N1a component. The patients had a larger peak-to-peak difference than controls (1.63 vs. 0.62 microV). The P1 and N1a are cortically generated potentials. Patients with focal dystonia had an increase in activity compared to controls when processing simple auditory stimuli. Such changes in electrophysiological responses may be a result of increases in excitation or lack of inhibition; alternatively the changes may represent cross-modal maladaptive plasticity from the somatosensory modality to the auditory modality. Thus, this study provides further evidence that patients with focal dystonia have alterations of the central nervous system that are not limited to their symptomatic sensory domain.

Contingent negative variation elicited before jaw and tongue movements

Contingent negative variation (CNV) is a negative brain potential occurring between two successive stimuli when the first stimulus is a warning and the second stimulus requires a motor response. The CNV is interpreted as an expression of the cognitive processes in preparation for a response directed to a purpose. Using 19 electrodes we recorded CNVs for mouth opening, closing and lateral movements, tongue protrusion and hand extension in 10 healthy subjects. The aim of the study was to examine the motor control mechanism underlying jaw and tongue movements in a cognitive paradigm. The first stimulus (S1) served as a preparatory warning signal for the imperative stimulus (S2) 2 s after the S1. The subject performed the experimental tasks after the S2. The grand average CNVs for jaw and tongue movements showed a bilaterally widespread negativity with the maximum in the vertex region (Cz). The early CNV was identified about 400 ms after the S1 and its amplitude was highest at the midline-frontal area. The late CNV started approximately 1000 ms after the S1 with the maximum at Cz. The mean amplitude was significantly lower for hand extension than for the other tasks, and significantly higher for lateral movement than for mouth closing, suggesting that the CNV amplitude can be affected by the complexity of the task. The CNV recording may provide a means to study the neuronal activity necessary for the sensorimotor integration of jaw and tongue movements.

Silent event-related fMRI reveals deficient motor and enhanced somatosensory activation in orofacial dystonia

Previous studies showed cortical dysfunction and impaired sensorimotor integration in primary generalized and focal hand dystonia. We used a whistling task and silent event-related fMRI to investigate functional changes in patients with blepharospasm and patients with a combination of blepharospasm and oromandibular dystonia (Meige's syndrome). Whistling served as a model for a skilful orofacial movement with a high demand on sensorimotor integration. It allowed us to study the oromandibular motor system that is clinically affected in Meige's syndrome but not in isolated blepharospasm. In Meige's syndrome, functional MRI revealed deficient activation of the primary motor and ventral premotor cortex within the mouth representation area during whistling. Compared with healthy controls, both forms of orofacial dystonia had increased activation of bilateral somatosensory areas and the caudal supplementary motor area (SMA) in common. While overactivity of somatosensory areas and caudal SMA in Meige patients was partly reversed by botulinum toxin treatment, impaired motor activation was not. We conclude that impaired motor activation appears to be specific for the clinically affected oromandibular motor system in Meige's syndrome while enhanced somatosensory activation is a common abnormality in both forms of orofacial dystonia independent of the affected motor system. Somatosensory overactivity indicates an altered somatosensory representation in orofacial dystonia while impaired motor activation may be a functional correlate of reduced cortical inhibition during oromandibular motor execution in Meige's syndrome.

Electroencephalographic spectral power in writer's cramp patients: evidence for motor cortex malfunctioning during the cramp

We investigated cortical activation as reflected in task-related spectral power (TRPow) changes in 8 writer's cramp patients during writing on a digital board and during isometric contraction and compared them to those of 8 age-matched healthy subjects. Scalp EEG was recorded over the contralateral primary sensorimotor area (SM1(c)), and from the ipsilateral sensorimotor area (SM1(i)). The electromyogram (EMG) was recorded from the Extensor Digitorum Communis (Extensor), Flexor Digitorum Superficialis (Flexor), and First Dorsal Interosseous (FDI) muscles. We analyzed (1) handwriting performance, (2) changes in the TRPow confined to alpha and beta band, and (3) the EMG spectral power during both tasks, writing and isometric contraction. During writing, all patients developed writer's cramp. The handwriting in writer's cramp patients was associated with significantly less reduction of the beta-range TRPow and lower frequency of the TRPow reduction compared to controls. No significant differences between patients and controls for the alpha band TRPow reduction during handwriting were observed. During writing, the patients showed higher EMG spectral power than the controls but this difference was at the border of significance. The present results indicate disorder in the motor execution system, in writer's cramp patients, associated with impaired functional beta-network state of the contra- and ipsilateral sensorimotor cortices, most probably due to inadequate modulation of the intracortical inhibition associated with writing.

Oscillatory coupling in writing and writer's cramp

Writing is a highly skilled and overlearned movement. In patients suffering from writer's cramp, a focal task-induced dystonia, writing is impaired or even impossible due to involuntary muscle contractions and abnormal posture, which occur as soon as the person picks up a pen or within writing a few words. The underlying pathophysiological mechanisms of this movement disorder are not fully understood up to now. The aim of the present study was to unravel the oscillatory network underlying physiological writing in healthy subjects and dystonic writing in writer's cramp patients. Using whole-head magnetoencephalography (MEG) and the analysis tool dynamic imaging of coherent sources (DICS) we studied oscillatory neural coupling during writing in eleven healthy subjects and eight patients suffering from writer's cramp. Simultaneous recording of brain activity with MEG and activity of forearm and hand muscles with surface electromyography (EMG) was performed while subjects were writing for five minutes with their dominant right hand. Applying DICS sources of strongest cerebro-muscular coherence and cerebro-cerebral coherence during writing were identified, which consistently included six brain areas in both, the control subjects and the patients: contralateral and ipsilateral sensorimotor cortex, ipsilateral cerebellum, contralateral thalamus, contralateral premotor and posterior parietal cortex. Coherence between cortical sources and muscles appeared primarily in the frequency of writing movements (3-7 Hz) while coherence between cerebral sources occurred primarily around 10 Hz (8-13 Hz). Interestingly, consistent coupling between both sensorimotor cortices was observed in patients only, whereas coupling between ipsilateral cerebellum and the contralateral posterior parietal cortex was found in control subjects only. These results are consistent with the often described bilateral pathophysiology and impaired sensorimotor integration in writer's cramp patients.

Abnormalities of sensory processing and sensorimotor interactions in secondary dystonia: a neurophysiological study in two patients

Experimental data suggest that abnormalities of sensory processing and sensorimotor integration may play a role in the genesis of symptoms in primary dystonia. We studied 2 patients with dystonia secondary to lesions in the somatosensory pathways. We documented sensorimotor alterations in these patients that strongly resemble those found in primary dystonia. Our data are consistent with the hypothesis that abnormalities in sensorimotor processing may contribute to the pathogenesis of dystonic conditions.

Corticospinal excitability accompanying ballistic wrist movements in primary dystonia

Current models of basal ganglia dysfunction in primary dystonia propose that the excessive muscle activity results from an increase in the excitability of the primary motor cortex. Neurophysiological and neuroimaging studies, however, have shown consistently reduced movement-related sensorimotor cortical activity. To explore this paradox, we used transcranial magnetic stimulation (TMS) to examine changes in corticospinal excitability preceding and during ballistic movements of the wrist in 9 patients with primary dystonia affecting the arm and 9 matched control subjects. The onset time, rate of rise, and duration of changes in the excitability of corticospinal projections to the agonist muscle were normal in the patients with dystonia. Increases in excitability were selective to the initial agonist muscle, suggesting that the spatial recruitment of corticospinal neurons was normal. Nonetheless, movements were slower in the patients by an average of 26%. The onset of the first agonist muscle burst was normal in magnitude and timing but the activity in this muscle subsequently became attenuated as movement progressed. Muscle activity in antagonist and proximal muscles of the upper arm was reduced significantly in the dystonia patients. These findings support the view that movement preparation and initiation at the level of the primary motor cortex is normal in patients with dystonia. Bradykinesia could not be attributed to co-contraction or overflow of activity and was associated with reduced rather than excessive muscle activity.

Task-specific plasticity of somatosensory cortex in patients with writer's cramp

Focal dystonias such as writer's cramp are characterized by muscular cramps that accompany the execution of specific motor tasks. Until now, the pathophysiology of focal dystonia remains incompletely understood. Recent studies suggest that the development of writer's cramp is related to abnormal organization of primary somatosensory cortex (SI), which in turn leads to impaired motor function. To explore contributions of SI on mechanisms of task specificity in focal dystonia, we investigated dynamic alterations in the functional organization of SI as well as sensory-motor gating for rest, left- and right-handed writing and brushing in writer's cramp patients and healthy controls. The functional organization of somatosensory cortex was assessed by neuromagnetic source imaging (151 channel whole-head MEG). In accordance with previous reports, distances between cortical representations of thumb and little finger of the affected hand were smaller in patients compared to healthy subjects. However, similar to healthy controls, patients showed normal modulation of the functional organization of SI as induced by the execution of different motor tasks. Both in the control subjects and patients, cortical distances between representations of thumb and little finger increased when writing and brushing compared to the resting condition. Although, cramps only occured during writing, no differences in the organization of SI were seen among motor tasks. Our data suggest that despite alterations in the organization of primary somatosensory cortex in writer's cramp, the capability of SI to adapt dynamically to different tasks is not impaired.

Motor preparation is more impaired in Parkinson's disease when sensorimotor integration is involved

OBJECTIVE

This study aimed to investigate changes in spatio-temporal, event-related (de)synchronization (ERD/ERS) patterns recorded with respect to the more akinetic versus the less akinetic side during performance of a visuo-guided targeting movement when compared to an index finger extension.

METHODS

Twelve de novo parkinsonian patients were recorded. ERD/ERS in mu and beta frequency bands was computed from 21 source derivations.

RESULTS

When the index finger extension was performed with the less akinetic limb, mu ERD focused over contralateral central region appeared 2 s before movement. With the targeting movement, additional pre-movement mu ERD was observed over the parietal region, as well as earlier ipsilateral mu ERD. When the same movements were performed with the more akinetic limb, we observed delayed mu ERD over contralateral regions, earlier ipsilateral mu ERD and a lack of contralateral parietal mu ERD before the targeting movement. Following index finger extension for the less akinetic limb, a focused contralateral central beta ERS was recorded, increasing and spreading after the targeting movement. In contrast, for the more akinetic limb, beta ERS was dramatically attenuated and remained unchanged after the targeting movement.

CONCLUSIONS

These results confirm the fact that motor programming is delayed, and provide some insight into what may well be impaired sensorimotor integration in Parkinson's disease.

Sensorimotor integration in movement disorders

Although current knowledge attributes movement disorders to a dysfunction of the basal ganglia-motor cortex circuits, abnormalities in the peripheral afferent inputs or in their central processing may interfere with motor program execution. We review the abnormalities of sensorimotor integration described in the various types of movement disorders. Several observations, including those of parkinsonian patients' excessive reliance on ongoing visual information during movement tasks, suggest that proprioception is defective in Parkinson's disease (PD). The disturbance of proprioceptive regulation, possibly related to the occurrence of abnormal muscle-stretch reflexes, might be important for generating hypometric or bradykinetic movements. Studies with somatosensory evoked potentials (SEPs), prepulse inhibition, and event-related potentials support the hypothesis of central abnormalities of sensorimotor integration in PD. In Huntington's disease (HD), changes in SEPs and long-latency stretch reflexes suggest that a defective gating of peripheral afferent input to the brain might impair sensorimotor integration in cortical motor areas, thus interfering with the processing of motor programs. Defective motor programming might contribute to some features of motor impairment in HD. Sensory symptoms are frequent in focal dystonia and sensory manipulation can modify the dystonic movements. In addition, specific sensory functions (kinaesthesia, spatial-temporal discrimination) can be impaired in patients with focal hand dystonia, thus leading to a "sensory overflow." Sensory input may be abnormal and trigger focal dystonia, or defective "gating" may cause an input-output mismatch in specific motor programs. Altogether, several observations strongly support the idea that sensorimotor integration is impaired in focal dystonia. Although elemental sensation is normal in patients with tics, tics can be associated with sensory phenomena. Some neurophysiological studies suggest that an altered "gating" mechanism also underlies the development of tics. This review underlines the importance of abnormal sensorimotor integration in the pathophysiology of movement disorders. Although the physiological mechanism remains unclear, the defect is of special clinical relevance in determining the development of focal dystonia.

Aberrant Sensorimotor Integration in Musicians' Cramp Patients

AbstractSimple tapping and complex movements (Luria finger apposition task) were performed unimanually and bimanually by two groups of professional guitarists while EEG was recorded from electrodes over the sensorimotor cortex. One group had a task-specific movement disorder (focal dystonia or musicians' cramp), while the other group did not (controls). There were no significant group interactions in the task-related power (TRPow) within the alpha range of 8-10Hz (mu1). In contrast, there was a significant group interaction within the alpha range of 10-12Hz (mu2); these latter frequencies are associated with task-specific sensorimotor integration. The significant group interaction included task (simple and complex) by hand (left, right, and both) by electrodes (10 electrodes over the sensorimotor areas). In the rest conditions, the alpha power (10-12Hz) was comparable between the groups; during movement, however, compared to the controls, patients demonstrated the greatest TRPow (10-12Hz) over all conditions. This was particularly evident when patients used their affected hand and suggests that patients with musicians' cramp have impaired task-specific sensorimotor integration.

Abnormal somatotopic arrangement of sensorimotor interactions in dystonic patients

The aim of the study was to detect abnormalities of sensorimotor interactions and their topographic distribution in the hand muscles of dystonic patients. We investigated the effect of electrical stimulation of the second (D2) and fifth (D5) fingers on the amplitude of motor evoked potentials (MEPs) in response to transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (TES) in the relaxed first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles on both sides of eight patients with unilateral hand dystonia (HD) and in four patients with cervical dystonia (CD). Six Parkinson's disease patients were used as the disease control group and 10 healthy subjects served as normal controls. For each muscle, the digital stimulation was applied to a contiguous finger (CF) and to a non-contiguous finger (NCF). The digital stimulation was set at three times the sensory threshold and preceded TMS or TES at intervals ranging from 10 to 100 ms. In normal subjects, a somatotopic inhibitory effect was detected, since the CF stimulation was significantly more powerful in determining the reduction of MEPs in response to TMS at intervals ranging from 20 to 50 ms. In dystonic patients, on the contrary, the somatopic effect was not present, because both CF and NCF stimulation evoked a consistent MEP inhibition and no significant difference was detected between the conditioning effect of CF and NCF stimulation. These abnormalities were present in the muscles of both the affected and unaffected hands of HD patients, as well as in CD patients. TES conditioning provoked MEP inhibition only at interstimulus intervals (ISIs) <40 ms. Significant MEP potentiation was found at ISIs of 20-40 ms to CF stimulation in Parkinson's disease patients, while there was no effect after NCF stimulation. These data suggest that MEP suppression in response to digital stimulation is preserved in dystonia, but the somatotopically distributed input-output organization of the sensorimotor interactions is lost in dystonic patients' hands. The comparison between TMS and TES experiments indicates that abnormalities may be present at both the spinal and the cortical level, at least in some patients. These findings suggest that a mechanism that normally operates in order to focus the effect of somatosensory afferences on the motor system may be impaired in dystonia. This abnormality seems specific to dystonia.

Dystonia: a disorder of motor programming or motor execution?

For some time, dystonia has been seen as purely a motor disorder. Relatively novel concepts published approximately 10 years ago also presumed that in the development of dystonic dyskinesias, only motor behaviour was abnormal. Neurophysiological observations of various types of dystonic disorders, which were performed using sophisticated electromyography, polymyography, H-reflex examination, long-latency reflex, etc., as well as new insights into the behaviour of dystonia, have urged the inclusion of sensory (particularly somatosensory) mechanisms into the pathophysiological background of dystonia. The major role has been considered to be played by abnormal proprioceptive input by means of the Ia proprioceptive afferents, with the source of this abnormality found in the abnormal processing of muscle spindle afferent information. However, neurophysiological investigations have also provided evidence that the abnormality in the central nervous system is located not only at the spinal and subcortical level, but also at the cortical level; specifically, the cortical excitability and intracortical inhibition have been revealed as abnormal. This evidence was revealed by SEP recordings, paired transcranial magnetic stimulation recordings, and BP and CNV recordings. The current concept of dystonic movement connects the abnormal function of somatosensory pathways and somatosensory analysers with the dystonic performance of motor action, which is based on the abnormality of sensorimotor integration.

Focal dystonia: current theories

Dystonia is a syndrome characterised by abnormal involuntary sustained muscle contractions that often result in twisted and abnormal positions. Focal dystonia affects only a single body part with symptoms varying from permanent (e.g., torticollis) to task-specific (e.g., musician's cramp). The exact causes of focal dystonia have yet to be determined. Possible causative factors have been identified at all levels along the sensorimotor pathway, including anatomical constraints of the hand (musicians), abnormal co-contractions of the muscles due to reciprocal inhibition in the spinal cord, subcortical and cortical remapping, deficiencies in sensorimotor integration and perceptual deficits. A review of the current literature on these topics is provided with a special focus on musicians with focal dystonia. Also reviewed are current treatments of focal dystonia in musicians. On the basis of the currently available evidence, certain risk factors are identified for the development of task-specific focal dystonia, including number of practice hours, personality, genetic predisposition, performance factors and sensory effects. In addition, it is highlighted that dystonic movements occur predominantly in the context of perceptual-motor tasks involving emotions. When emotional and motor traces have become associated, they are difficult to change; it is suggested that this mechanism plays an important role in the preservation of dystonic symptoms.

Cognitive response control in writer's cramp

Disturbances of the motor and sensory system as well as an alteration of the preparation of movements have been reported to play a role in the pathogenesis of dystonias. However, it is unclear whether higher aspects of cortical - like cognitive - functions are also involved. Recently, the NoGo-anteriorization (NGA) elicited with a visual continuous performance test (CPT) during recording of a 21-channel electroencephalogram has been proposed as an electrophysiological standard-index for cognitive response control. The NGA consists of a more anterior location of the positive area of the brain electrical field associated with the inhibition (NoGo-condition) compared with that of the execution (Go-condition) of a prepared motor response in the CPT. This response control paradigm was applied in 16 patients with writer's cramp (WC) and 14 age matched healthy controls. Topographical analysis of the associated event-related potentials revealed a significant (P < 0.05) NGA effect for both patients and controls. Moreover, patients with WC showed a significantly higher global field power value (P < 0.05) in the Go-condition and a significantly higher difference-amplitude (P < 0.05) in the NoGo-condition. A source location analysis with the low resolution electromagnetic tomography (LORETA) method demonstrated a hypoactivity for the Go-condition in the parietal cortex of the right hemisphere and a hyperactivity in the NoGo-condition in the left parietal cortex in patients with WC compared with healthy controls. These results indicate an altered response control in patients with WC in widespread cortical brain areas and therefore support the hypothesis that the pathogenesis of WC is not restricted to a pure sensory-motor dysfunction.