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Abnormal sensory homunculus in dystonia of the hand
Annals of Neurology
Abstract
Abnormalities of the sensory system have been proposed as causative factors for dystonia By mapping the human cortical hand somatosensory area of 6 patients with focal dystonia of the hand, we found an abnormality of the normal homuncular organization of the finger representations in the primary somatosensory cortex (S1). Although a remote antecedent event or even a developmental anomaly cannot entirely be ruled out, our findings may support the concept that abnormal plasticity is involved in the development of dystonia.
... pBreusch-Pagan=0. 51), no dystonia-dependent interaction effect was found. There was a main effect of Foot-SCAN FC higher than CON-SCAN across all groups (p=0.016) ...
... Accurate estimation of individual brain network variations has been a challenge especially in taskspecific focal dystonia, where prior research identified topographical changes in effector networks during task 14,32,34-36 perhaps due to sensorimotor reorganization. 33,51,52 In this study, we applied a task-based ROI definition and resting-state parcellation on an individual level to compute functional connectivity in focal dystonia. The significant Task Vocal, but not Rest Mouth, dystonia-related changes may suggest that the individual variability in motor tasks is important for focal dystonia pathology and cannot be fully captured in resting-state scans. ...
The central pathology causing idiopathic focal dystonia remains unclear, limiting effective treatment targets. The recently identified somato-cognitive action network (SCAN) with its role in coordinating physiologic processes and coarse movements has been implicated in dystonia dysfunction. SCAN is thought to interface between the phylogenetically newer primary motor regions that control fine movements and the cingulo-opercular network (CON) that putatively conveys cognitive intentions for action. We hypothesized that the effector-agnostic nature of SCAN may constitute a central pathology shared across focal dystonia subtypes affecting different body parts. Additionally, the effector-specific areas in the primary sensorimotor cortex may show distinct functional changes depending on the dystonic body region.
We collected functional MRI from people with either of two subtypes of idiopathic focal dystonia (laryngeal dystonia or LD, N =24, and focal hand dystonia or FHD, N =18) and healthy control participants ( N =21). Regions of interest were selected based on prior work that suggested dystonia-related abnormality within the basal-ganglia-thalamo-cortical and cerebello-thalamo-cortical sensorimotor pathways. We investigated if focal dystonia is associated with resting-state functional connectivity changes 1) between SCAN and other cortical regions (effector-specific areas and CON), 2) between cortical and non-cortical regions, or 3) between non-cortical (subcortical and cerebellar) regions. Cortical regions of interest were individualized based on resting-state data. Separately, individualized hand and mouth/larynx regions were also generated from task-based MRI (finger-tapping and phonation, respectively) for comparison.
Results showed a significant interaction effect in both focal dystonia subtypes ( p =0.048 for LD, p =0.017 for FHD) compared to controls, which was driven by SCAN’s higher functional connectivity to task-derived mouth/larynx region and concomitantly lower connectivity to CON. This dystonia-dependent interaction was not observed with the resting-state mouth/larynx region. No significant resting-state functional changes were observed involving subcortical and cerebellar regions when LD and FHD were modeled as independent groups. However, exploratory analysis combining LD and FHD as a single group suggested a dystonia-dependent asynchronization between SCAN and sensorimotor cerebellum ( p =0.051) that may suggest a pathological rather than compensatory process.
For the first time, our study systematically tested key functional connectivity changes in two focal dystonias. Our results show that SCAN is uniquely associated with dystonia dysfunction beyond the dystonic effector regions, potentially offering insights on pathophysiology and future treatments.
... However, one needs consider the known pathophysiology of CD that is characterized by abnormal overlapping neural representations of body and muscle systems in somatosensory and motor cortex. Such "smeared" cortical representations could also explain why responses to VTS were not specific to a single muscle site [26]. Moreover, for individual participants reporting pain relief, the perceived reduction in pain occurred quickly within seconds and was not identical across all muscle sites, features that are difficult to reconcile with an unspecific placebo response. ...
Pain is a common non-motor symptom in patients with cervical dystonia (CD), severely impacting their quality of life. The pathophysiology of CD is incompletely understood but it involves altered processing of proprioceptive and pain signals.
The purpose of this proof-of-concept study was to determine if vibro-tactile stimulation (VTS)—a non-invasive form of neuromodulation targeting the somatosensory system—can modulate neck pain in people with CD.
In a multi-center study, 44 CD patients received VTS to sternocleidomastoid and/or trapezius muscles for up to 45 min under 9 different stimulation conditions that either targeted a single or a pair of muscles. The primary outcome measure was a perceived pain score (PPS) rated by participants on a 100-point analogue scale.
During VTS, 29/44 (66%) of participants experienced a reduction in PPS of at least 10% with 17/44 (39%) reporting a reduction in pain of 50% or higher. After VTS cessation, 57% of participants still reported a 10% or higher reduction in PPS. Effects were significant at the group level and persisted for up to 20 min post-treatment. No distinct optimal stimulation profiles were identified for specific CD phenotypes. Clinical markers of disease severity or duration did not predict the degree of VTS-induced pain reduction.
This proof-of-concept study demonstrates the potential of VTS as a new non-invasive therapeutic option for treating neck pain associated with CD. Further research needs to delineate optimal dosage and long-term effects.
... 3,55 A typical example is freezing of gait, that is, an inability to move, which may suddenly occur, particularly in narrow spaces both in real situations and in virtual reality environments. 56 In dystonia, there is ample evidence for altered central perceptual processing 57 and altered cortical representation of perceptual, particularly sensory information, 58 which is illustrated, for example, by the clinical phenomenon that applying vibration to the hands of people with focal limb dystonia or graphospasm can induce or worsen dystonic movements. 12,59 Dystonic arm tremor is often positionspecific, becoming worse in certain positions, 60 underscoring the role of proprioceptive input. ...
At present, clinical practice and research in movement disorders focus on the “normalization” of altered movements. In this review, rather than concentrating on problems and burdens people with MDs undoubtedly have, we highlight their hidden potentials. Starting with current definitions of Parkinson’s disease, dystonia, chorea, and tics, we outline that solely conceiving these phenomena as signs of dysfunction falls short of their complex nature comprising both problems and potentials. Such potentials can be traced and understood in light of well-established cognitive neuroscience frameworks, particularly ideomotor principles, and their influential modern derivatives. Using these frameworks, the wealth of data on altered perception-action integration in the different movement disorders can be explained and systematized using the mechanism-oriented concept of perception-action binding. According to this concept, movement disorders can be understood as phenomena requiring and fostering flexible modifications of perception-action associations. Consequently, although conceived as being caught in a (trough) state of deficits, given their high flexibility, people with movement disorders also have high potential to switch to (adaptive) peak activity that can be conceptualized as hidden potentials. Currently, clinical practice and research in movement disorders are concerned with deficits and thus the “deep and wide troughs”, whereas “scattered narrow peaks” reflecting hidden potentials are neglected. To better delineate and utilize the latter to alleviate the burden of affected people, and destigmatize their conditions, we suggest some measures, including computational modelling combined with neurophysiological methods and tailored treatment.
Insights into the structure and function of the basal ganglia and their role in the pathophysiology of movement disorders resulted in the 1980s in the development of testable models of hypokinetic and hyperkinetic movement disorders. Further refinement in the 1990s resulted from continued research in animal models and the addition of physiological recordings of neuronal activity in humans undergoing functional neurosurgical procedures (1–7). These models have gained considerable practical value, guiding the development of new pharmacologic and surgical treatments, but, in their current form, more and more insufficiencies of these simplified schemes are becoming apparent. In the following chapter we discuss both models, as well as some of the most important criticisms.
Background
Musicians' dystonia (MD) is a movement disorder with several established risk factors, but the exact pathophysiology remains unknown. Recent research suggests dysfunction in sensory‐motor, basal ganglia, cerebellar, and limbic loops as potential causes. Adverse childhood experiences are also considered risk factors.
Objective
This study aimed to investigate whether MD patients have experienced more childhood trauma, leading to increased stress reactivity and neural vulnerability to movement disorders.
Methods
Using functional magnetic resonance imaging and the Montreal Imaging Stress Task, 40 MD patients were compared with 39 healthy musicians (HMs). Whole‐brain analysis and regions of interest analysis were performed. Parameter estimates and subjective stress levels were compared between groups and correlated with the Childhood Trauma Questionnaire.
Results
MD patients reported significantly higher childhood trauma scores than healthy control subjects, but they did not differ in their subjective stress experiences. Stress‐related activity of limbic areas was neither found in the whole sample nor between the two groups. Instead, increased activity of visual association and temporal areas was observed, but this activation did not differ between patients and HMs. However, patients showed a tendency toward reduced precuneus activity under stress. Adverse childhood experiences were negatively correlated with precuneus, thalamus, and substantia nigra activity across all participants.
Conclusions
Overall, MD patients and HMs had similar subjective and neurological reactions to stress but differed in childhood trauma experiences and precuneus activity under stress. Further research about the functional connectivity between precuneus, cerebellum, thalamus, and basal ganglia in musicians is needed. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.
Objective
To provide a comprehensive overview of rehabilitation treatment strategies for focal hand dystonia (FHD) in musicians, examining their evolution and effectiveness.
Data Sources
A systematic search of five databases, PubMed, PEDro, Cochrane Library, Trip, and Google Scholar, to identify relevant articles on FHD rehabilitation. The last search was performed on 20 December 2023.
Methods
Inclusion criteria were applied to 190 initially identified articles, resulting in 17 articles for review. Exclusions were made for duplicates, irrelevant titles, abstracts, and non-rehabilitation interventions.
Results
Ten different rehabilitation approaches were identified over 20 years. While no definitive intervention protocol exists, a multimodal approach is commonly recommended.
Conclusions
This scoping review underscores the diversity of rehabilitation strategies for FHD. It suggests the potential of multimodal approaches, emphasizing the need for further large-scale clinical efficacy studies.
Focal hand dystonia (FHD) is characterized by dystonic hand contractions that are often aggravated by purposeful actions and may be specific to a particular task. The term “occupational dystonia” is used when dystonia affecting performance of the job arises in individuals with a particular occupation, usually an occupation requiring repetitive and excessive fine motor activity.
One task-specific FHD, writer’s cramp, causes disabling spasms of the hands when attempting to write, and is particularly likely in people whose profession involves excessive writing. Musician’s dystonia (cramp) is applied to a focal dystonia localized to hand muscles controlling fine movements of the digits or the embouchure muscles involved in playing instruments.
Injection of botulinum neurotoxin (BoNT) is effective in writer’s cramp and other occupational dystonias. This chapter discusses the different common patterns of dystonic movement of the hand and arm, identifies the particular muscles active in each dystonia pattern to aid in target selectio, and illustrates the muscular anatomy and injection approach using anatomical diagrams. Guidance of injections with EMG is discussed. Dosing recommendations for three different BoNT formulations are tabulated.
The primate somatosensory cortex, which processes tactile stimuli, contains a topographic representation of the signals it receives, but the way in which such maps are maintained is poorly understood. Previous studies of cortical plasticity indicated that changes in cortical representation during learning arise largely as a result of hebbian synaptic change mechanisms. Here we show, using owl monkeys trained to respond to specific stimulus sequence events, that serial application of stimuli to the fingers results in changes to the neuronal response specificity and maps of the hand surfaces in the true primary somatosensory cortical field (S1 area 3b). In this representational remodelling stimuli applied asychronously to the fingers resulted in these fingers being integrated in their representation, whereas fingers to which stimuli were applied asynchronously were segregated in their representation. Ventroposterior thalamus response maps derived in these monkeys were not equivalently reorganized. This representational plasticity appears to be cortical in origin.
1. Temporal response characteristics of neurons were sampled in fine spatial grain throughout the hand representations in cortical areas 3a and 3b in adult owl monkeys. These monkeys had been trained to detect small differences in tactile stimulus frequencies in the range of 20-30 Hz. Stimuli were presented to an invariant, restricted spot on a single digit. 2. The absolute numbers of cortical locations and the cortical area over which neurons showed entrained frequency-following responses to behaviorally important stimuli were significantly greater when stimulation was applied to the trained skin, as compared with stimulation on an adjacent control digit, or at corresponding skin sites in passively stimulated control animals. 3. Representational maps defined with sinusoidal stimuli were not identical to maps defined with just-visible tapping stimuli. Receptive-field/frequency-following response site mismatches were recorded in every trained monkey. Mismatches were less frequently recorded in the representations of control skin surfaces. 4. At cortical locations with entrained responses, neither the absolute firing rates of neurons nor the degree of the entrainment of the response were correlated with behavioral discrimination performance. 5. All area 3b cortical locations with entrained responses evoked by stimulation at trained or untrained skin sites were combined to create population peristimulus time and cycle histograms. In all cases, stimulation of the trained skin resulted in 1) larger-amplitude responses, 2) peak responses earlier in the stimulus cycle, and 3) temporally sharper responses, than did stimulation applied to control skin sites. 6. The sharpening of the response of cortical area 3b neurons relative to the period of the stimulus could be accounted for by a large subpopulation of neurons that had highly coherent responses. 7. Analysis of cycle histograms for area 3b neuron responses revealed that the decreased variance in the representation of each stimulus cycle could account for behaviorally measured frequency discrimination performance. A strong correlation between these temporal response distributions and the discriminative performances for stimuli applied at all studied skin surfaces was even stronger (r = 0.98) if only the rising phases of cycle histogram were considered in the analysis. 8. The responses of neurons in area 3a could not account for measured differences in frequency discrimination performance. 9. These representational changes did not occur in monkeys that were stimulated on the same schedule but were performing an auditory discrimination task during skin stimulation. 10. It is concluded that by behaviorally training adult owl monkeys to discriminate the temporal features of a tactile stimulus, distributed spatial and temporal response properties of cortical neurons are altered.(ABSTRACT TRUNCATED AT 400 WORDS)
A functional-anatomical brain scanner that has a temporal resolution of less than a hundred milliseconds is needed to measure the neural substrate of higher cognitive functions in healthy people and neurological and psychiatric patients. Electrophysiological techniques have the requisite temporal resolution but their potential spatial resolution has been not realized. Here we briefly review progress in increasing the spatial detail of scalp-recorded EEGs and in registering this functional information with anatomical models of a person's brain. We describe methods and systems for 124-channel EEGs and magnetic resonance image (MRI) modeling, and present first results of the integration of equivalent-dipole EEG models of somatosensory stimulation with 3-D MRI brain models.
Occupational cramps affecting the upper extremities have been described for centuries, though only recently is light being shed on their pathogenesis, pathophysiology, and improved strategies for diagnosis and treatment. These dystonias represent localized stereotyped painless movement disorders affecting certain occupational groups in characteristic ways. We retrospectively reviewed 65 patients given a diagnosis of focal dystonias of the upper extremity and describe painless manual incoordination syndromes, insidious in onset, without objective sensory abnormalities, precipitated by certain repetitive actions of the upper extremity. This confirms previous clinical reports. Pathogenesis and pathophysiology are still uncertain, but evidence for altered higher order (basal ganglia and cortical) influences on spinal interneurons leading to ill-directed motor output is hypothesized. Therapeutic options are reviewed stressing the inadequacy of any one mode discovered to date.
We studied 19 patients with hand cramps, including writer's cramp, typist's cramp, piano, and guitar player's cramp. EMGs were recorded while patients performed the task triggering the cramps. Ten patients with dystonic cramps had EMGs with generalized muscle spasms with co-contraction of agonist and antagonist muscles. In three patients with simple cramps that involved one to three fingers, specific muscle groups showed co-contracting bursts that lasted longer than normal. The physiological abnormalities support the interpretation that hand cramp is a focal dystonia, characterized by both excessive muscle activity and defective fine motor control.
For quantitative assessment of the primary torsion dystonias, a rating scale is proposed that has two sections--a Movement Scale, based on examination, and a Disability Scale, based on the patient's statements about seven activities of daily living. We assessed the validity of the Movement Scale by comparing scores with a ranking of patients according to dystonia severity and with ratings of the patients on the Disability Scale. In addition, we assessed the inter-and intra-rater reliability of the scale by comparing independent scorings of patients by four examiners and by comparing scorings by the same examiners performed at different times. We found that the Movement Scale was a valid and reliable indicator of the severity of primary torsion dystonia.
The amplitude of the primary positive deflection, P24, was measured in each wave form recorded from a 36-channel scalp electrode array placed over sensorimotor cortex. Electrical stimulation of contralateral little, middle, index finger, or thumb produced wave forms possessing common features, but the location of peak P24 amplitude depended upon the digit stimulated. With thumb stimulation peak P24 amplitude was located approximately two-thirds the distance from midline to sylvian fissure, while stimulation of the other digits resulted in more medially located topographic peaks. These shifts correlate with previous descriptions of body-part representation in somatosensory cortex and suggest that at least certain wave form deflections recorded from the scalp provide accurate localization of their underlying neural generators.
We have examined 29 subjects with writers' cramp (and 4 with typists' and one with pianists' cramp) and have noted two major groupings, simple and dystonic. We have observed spread from one to the other. We have seen repeatedly, in patients with isolated simple writers' cramp certain subtle physical signs which are found also in other basal ganglia diseases. We have noted also the frequent association of other features of segmental and generalized dystonia in patients with dystonic writers' cramp. We have demonstrated that patients with isolated writers' cramp have no higher an incidence of psychiatric disturbance, as judged by formal Present State Examination, than the normal population. We conclude that isolated writers' cramp is a physical illness rather than a psychological disturbance, and that it is a focal dystonia.
Somatosensory evoked potentials (SEPs) to median nerve and finger stimulation were analyzed by means of spatio-temporal dipole modelling combined with 3D-NMR tomography in 8 normal subjects. The early SEPs were modelled by 3 equivalent dipoles located in the region of the brain-stem (B) and in the region of the contralateral somatosensory cortex (T and R). Dipole B explained peaks P14 and N18 at the scalp. Dipole T was tangentially oriented and explained the N20-P20, dipole R was radially oriented and modelled the P22. The tangential dipole sources T were located within a distance of 6 mm on the average and all were less than 9 mm from the posterior bank of the central sulcus. In 6 subjects the tangential sources related to finger stimulation arranged along the central sulcus according to the known somatotopy. The radial sources did not show a consistent somatotopic alignment across subjects. We conclude that the combination of dipole source analysis and 3D-NMR tomography is a useful tool for functional localization within the human hand somatosensory cortex.