Globus pallidus stimulation reduces frontal hyperactivity in tardive dystonia

GPi-DBS-induced brain metabolic activation in cervical dystonia

BACKGROUND

Deep brain stimulation (DBS) of the globus pallidus interna (GPi) is a highly efficacious treatment for cervical dystonia, but its mechanism of action is not fully understood. Here, we investigate the brain metabolic effects of GPi-DBS in cervical dystonia.

METHODS

Eleven patients with GPi-DBS underwent brain 18F-fluorodeoxyglucose positron emission tomography imaging during stimulation on and off. Changes in regional brain glucose metabolism were investigated at the active contact location and across the whole brain. Changes in motor symptom severity were quantified using the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS), executive function using trail making test (TMT) and parkinsonism using Unified Parkinson's Disease Rating Scale (UPDRS).

RESULTS

The mean (SD) best therapeutic response to DBS during the treatment was 81 (22)%. The TWSTRS score was 3.2 (3.9) points lower DBS on compared with off (p=0.02). At the stimulation site, stimulation was associated with increased metabolism, which correlated with DBS stimulation amplitude (r=0.70, p=0.03) but not with changes in motor symptom severity (p>0.9). In the whole brain analysis, stimulation increased metabolism in the GPi, subthalamic nucleus, putamen, primary sensorimotor cortex (PFDR<0.05). Acute improvement in TWSTRS correlated with metabolic activation in the sensorimotor cortex and overall treatment response in the supplementary motor area. Worsening of TMT-B score was associated with activation of the anterior cingulate cortex and parkinsonism with activation in the putamen.

CONCLUSIONS

GPi-DBS increases metabolic activity at the stimulation site and sensorimotor network. The clinical benefit and adverse effects are mediated by modulation of specific networks.

Deep Brain Stimulation in the Treatment of Tardive Dyskinesia

Tardive dyskinesia (TD) is a phenomenon observed following the predominantly long-term use of dopamine receptor blockers (antipsychotics) widely used in psychiatry. TD is a group of involuntary, irregular hyperkinetic movements, mainly in the muscles of the face, eyelid, lips, tongue, and cheeks, and less frequently in the limbs, neck, pelvis, and trunk. In some patients, TD takes on an extremely severe form, massively disrupting functioning and, moreover, causing stigmatization and suffering. Deep brain stimulation (DBS), a method used, among others, in Parkinson's disease, is also an effective treatment for TD and often becomes a method of last resort, especially in severe, drug-resistant forms. The group of TD patients who have undergone DBS is still very limited. The procedure is relatively new in TD, so the available reliable clinical studies are few and consist mainly of case reports. Unilateral and bilateral stimulation of two sites has proven efficacy in TD treatment. Most authors describe stimulation of the globus pallidus internus (GPi); less frequent descriptions involve the subthalamic nucleus (STN). In the present paper, we provide up-to-date information on the stimulation of both mentioned brain areas. We also compare the efficacy of the two methods by comparing the two available studies that included the largest groups of patients. Although GPi stimulation is more frequently described in literature, our analysis indicates comparable results (reduction of involuntary movements) with STN DBS.

Seven-year resolution of cervical dystonia after unilateral pallidotomy: A case report

Background

Reports on the long-term effects of pallidotomy for cervical dystonia remain scarce.

Case Description

We report a case of cervical dystonia successfully treated by unilateral pallidotomy. The patient was a 29-year-old man without past medical and family history of cervical dystonia. At the age of 28 years, neck rotation to the right with right shoulder elevation developed and gradually became worse. After symptoms failed to respond to repetitive botulinum toxin injections and oral medications, he underwent left pallidotomy, which resulted in significant improvement of cervical dystonia and shoulder elevation without surgical complications. At the 3-month evaluation, the symptoms completely improved. The Toronto Western Spasmodic Torticollis Rating Scale score dramatically improved from 39 points before surgery to 0 points at 7-year postoperative evaluation.

Conclusion

This case suggests that unilateral pallidotomy can be an alternative treatment option for cervical dystonia.

Neurobiological effects of deep brain stimulation: A systematic review of molecular brain imaging studies

Deep brain stimulation (DBS) is an established treatment for several brain disorders, including Parkinson's disease, essential tremor, dystonia and epilepsy, and an emerging therapeutic tool in many other neurological and psychiatric disorders. The therapeutic efficacy of DBS is dependent on the stimulation target, but its mechanisms of action are still relatively poorly understood. Investigating these mechanisms is challenging, partly because the stimulation devices and electrodes have limited the use of functional MRI in these patients. Molecular brain imaging techniques, such as positron emission tomography (PET) and single photon emission tomography (SPET), offer a unique opportunity to characterize the whole brain effects of DBS. Here, we investigated the direct effects of DBS by systematically reviewing studies performing an `on' vs `off' contrast during PET or SPET imaging. We identified 62 studies (56 PET and 6 SPET studies; 531 subjects). Approximately half of the studies focused on cerebral blood flow or glucose metabolism in patients Parkinson's disease undergoing subthalamic DBS (25 studies, n = 289), therefore Activation Likelihood Estimation analysis was performed on these studies. Across disorders and stimulation targets, DBS was associated with a robust local increase in ligand uptake at the stimulation site and target-specific remote network effects. Subthalamic nucleus stimulation in Parkinson's disease showed a specific pattern of changes in the motor circuit, including increased ligand uptake in the basal ganglia, and decreased ligand uptake in the primary motor cortex, supplementary motor area and cerebellum. However, there was only a handful of studies investigating other brain disorder and stimulation site combinations (1-3 studies each), or specific neurotransmitter systems, preventing definitive conclusions of the detailed molecular effects of the stimulation in these cases.

Cerebellar tDCS as Therapy for Cerebellar Ataxias

In recent years, a growing body of literature has investigated the use of non-invasive brain stimulation (NIBS) techniques to influence cerebellar activity and the effects of cerebellar stimulation on other brain regions through its multiple complex projections. From the early 1990s, with the discovery of the so-called cerebellar inhibition (CBI), several studies have focused their attention on the use of cerebellar NIBS as treatment for different motor disorders. Cerebellar ataxias (CAs) represent the prototypical clinical manifestation of cerebellar alterations, but other movement disorders, such as Parkinson's disease, essential tremor, and dystonia have also been associated with alterations of networks which include the cerebellum, or of the cerebellum itself. Cerebellar transcranial direct current stimulation (ctDCS) could indeed represent an economical, non-invasive therapeutic tool with minimal side effects, thus improving the clinical management of patients and their quality of life. Studies show that ctDCS is effective as a therapeutic option for motor symptoms in patients with CAs, and especially in those with less severe forms, suggesting that ctDCS efficacy could result from augmented neuronal compensation, which itself relies on preserved cerebellar volume. Evidence for the efficacy of ctDCS is less conclusive for the other aforementioned motor disorders, although preliminary results are promising. Future studies should adopt more rigorous methods (e.g., larger sample sizes, double blinding, better characterization of the sample, reliable biomarkers), in order to allow the scientific community to derive higher-quality evidence on the efficacy of ctDCS as a therapeutic option for motor disorders.

Dystonia and Cerebellum: From Bench to Bedside

Dystonia pathogenesis remains unclear; however, findings from basic and clinical research suggest the importance of the interaction between the basal ganglia and cerebellum. After the discovery of disynaptic pathways between the two, much attention has been paid to the cerebellum. Basic research using various dystonia rodent models and clinical studies in dystonia patients continues to provide new pieces of knowledge regarding the role of the cerebellum in dystonia genesis. Herein, we review basic and clinical articles related to dystonia focusing on the cerebellum, and clarify the current understanding of the role of the cerebellum in dystonia pathogenesis. Given the recent evidence providing new hypotheses regarding dystonia pathogenesis, we discuss how the current evidence answers the unsolved clinical questions.

Task-related brain activity and functional connectivity in upper limb dystonia: a functional magnetic resonance imaging (fMRI) and functional near-infrared spectroscopy (fNIRS) study

Significance: Dystonia is a dynamic and complex disorder. Real-time analysis of brain activity during motor tasks may increase our knowledge on its pathophysiology. Functional near-infrared spectroscopy (fNIRS) is a noninvasive method that enables the measurement of cortical hemodynamic activity in unconstrained environments. Aim: We aimed to explore the feasibility of using fNIRS for the study of task-related brain activity in dystonia. Task-related functional magnetic resonance imaging (fMRI) and resting-state functional connectivity were also analyzed. Approach: Patients with idiopathic right-upper limb dystonia and controls were assessed through nonsimultaneous fMRI and fNIRS during a finger-tapping task. Seed-based connectivity analysis of resting-state fMRI was performed in both groups. Results: The fMRI results suggest nonspecific activation of the cerebellum and occipital lobe in dystonia patients during the finger-tapping task with the affected hand. Moreover, fNIRS data show lower activation in terms of oxyhemoglobin and total hemoglobin in the frontal, ipsilateral cortex, and somatosensory areas during this task. In dystonia, both fMRI and fNIRS data resulted in hypoactivation of the frontal cortex during finger tapping with both hands simultaneously. Resting-state functional connectivity analysis suggests that the cerebellar somatomotor network in dystonia has an increased correlation with the medial prefrontal cortex and the paracingulate gyrus. Conclusions: These data suggest that unbalanced activation of the cerebellum, somatosensory, and frontal cortical areas are associated with dystonia. To our knowledge, this is the first study using fNIRS to explore the pathophysiology of dystonia. We show that fNIRS and fMRI are complementary methods and highlight the potential of fNIRS for the study of dystonia and other movement disorders as it can overcome movement restrictions, enabling experiments in more naturalistic conditions.

Lessons learned from the syndrome of oculopalatal tremor

The syndrome of oculopalatal tremor (OPT) featuring the olivo-cerebellar hypersychrony leads to disabling pendular nystagmus and palatal myoclonus. This rare disorder provides valuable information about the motor physiology and offers insights into the mechanistic underpinning of common movement disorders. This focused review summarizes the last decade of OPT research from our laboratory and addresses three critical questions: 1) How the disease of inferior olive affects the physiology of motor learning? We discovered that our brain's ability to compensate for the impaired motor command and implement errors to correct future movements could be affected if the cerebellum is occupied in receiving and transmitting the meaningless signal. A complete failure of OPT patients to adapt to change in rapid eye movements (saccades) provided proof of this principle. 2) Whether maladaptive olivo-cerebellar circuit offers insight into the mechanistic underpinning of the common movement disorder, dystonia, characterized by abnormal twisting and turning of the body part. We discovered that the subgroup of patients who had OPT also had dystonia affecting the neck, trunk, limbs, and face. We also found that the subjects who had tremor predominant neck dystonia (without OPT) also had impaired motor learning on a long and short timescale, just like those with OPT. Altogether, our studies focused on dystonia suggested the evidence for the maladaptive olive-cerebellar system. 3) We discovered that the OPT subjects had difficulty in perceiving the direction of their linear forward motion, i.e., heading, suggesting that olivo-cerebellar hypersynchrony also affects perception.

Switching antipsychotic treatment to aripiprazole in psychotic patients with neuroleptic-induced tardive dyskinesia: a 24-week follow-up study

Aripiprazole is a second-generation antipsychotics, acting as a partial dopamine D2 receptor agonist. Previous studies on aripiprazole for tardive dyskinesia (TD) treatment were limited and inconclusive. This study was aimed to examine the effectiveness of aripiprazole in psychotic patients with a pre-existing TD. This was an open-label 24-week prospective cohort study conducted in a public mental hospital in Northern Taiwan from January 2009 to February 2010. Psychotic patients were cross-titrated of prior antipsychotics with aripiprazole, and the severity of TD was assessed at baseline and at weeks 2, 4, 8, 12, 16, 20, and 24. The primary study outcome was the change of TD severity, assessed by Abnormal Involuntary Movement Scale (AIMS) total score. Responder was defined as the reduction of AIMS total scores of no less than 50% from baseline to the study endpoint (24 weeks). Thirty psychotic patients with neuroleptic-induced TD were recruited. The AIMS total scores significantly decreased from baseline to the study endpoint (-7.17±5.55). The significant decrease of AIMS total scores started at week 2 (P<0.0001), and the change remained significant throughout the entire study period (P<0.0001). A greater severity of TD (adjusted odds ratio: 1.35, 95% confidence interval: 1.04-1.76, P=0.03) or a lower severity of parkinsonism (adjusted odds ratio: 0.78, 95% confidence interval: 0.61-0.99, P=0.04) at baseline was significantly associated with treatment responders. Our findings implicated that aripiprazole can be a promising treatment for clinicians considering drug switch in psychotic patients with TD. Further large randomized, controlled trials are warranted to confirm our findings.

How Many Types of Dystonia? Pathophysiological Considerations

Dystonia can be seen in a number of different phenotypes that may arise from different etiologies. The pathophysiological substrate of dystonia is related to three lines of research. The first postulate a loss of inhibition which may account for the excess of movement and for the overflow phenomena. A second abnormality is sensory dysfunction which is related to the mild sensory complaints in patients with focal dystonias and may be responsible for some of the motor dysfunction. Finally, there are strong pieces of evidence from animal and human studies suggesting that alterations of synaptic plasticity characterized by a disruption of homeostatic plasticity, with a prevailing facilitation of synaptic potentiation may play a pivotal role in primary dystonia. These working hypotheses have been generalized in all form of dystonia. On the other hand, several pieces of evidence now suggest that the pathophysiology may be slightly different in the different types of dystonia. Therefore, in the present review, we would like to discuss the neural mechanisms underlying the different forms of dystonia to disentangle the different weight and role of environmental and predisposing factors.

Chronic deep brain stimulation normalizes scalp EEG activity in isolated dystonia

OBJECTIVE

To investigate cortical activity using scalp EEG in patients with isolated dystonia treated with chronic deep brain stimulation (DBS), on and off stimulation.

METHODS

We analyzed 64-channel scalp EEG in 12 isolated dystonia patients treated with chronic DBS (7 generalized, 5 cervical/segmental; 7 globus pallidus (GP), 5 subthalamic nucleus (STN)), and 20 healthy age-matched controls. Recordings during rest and movement task, and clinical motor scores, were collected with DBS-on and during a 90-min DBS washout.

RESULTS

Resting state alpha power in the dominant (or contralateral to more dystonic side) motor cortex channel during DBS was comparable to healthy controls, but it increased when DBS was stopped. Resting state and movement-related alpha coherence between bilateral motor cortex channels was increased off DBS.

CONCLUSIONS

Chronic DBS reduces exaggerated alpha oscillations and interhemispheric alpha coherence in the motor cortex of patients with isolated dystonia.

SIGNIFICANCE

These findings complement related studies in Parkinson's disease and support the view that network desynchronization is a prominent mechanism of DBS in movement disorders.

Current Opinions and Areas of Consensus on the Role of the Cerebellum in Dystonia

A role for the cerebellum in causing ataxia, a disorder characterized by uncoordinated movement, is widely accepted. Recent work has suggested that alterations in activity, connectivity, and structure of the cerebellum are also associated with dystonia, a neurological disorder characterized by abnormal and sustained muscle contractions often leading to abnormal maintained postures. In this manuscript, the authors discuss their views on how the cerebellum may play a role in dystonia. The following topics are discussed: The relationships between neuronal/network dysfunctions and motor abnormalities in rodent models of dystonia. Data about brain structure, cerebellar metabolism, cerebellar connections, and noninvasive cerebellar stimulation that support (or not) a role for the cerebellum in human dystonia. Connections between the cerebellum and motor cortical and sub-cortical structures that could support a role for the cerebellum in dystonia. Overall points of consensus include: Neuronal dysfunction originating in the cerebellum can drive dystonic movements in rodent model systems. Imaging and neurophysiological studies in humans suggest that the cerebellum plays a role in the pathophysiology of dystonia, but do not provide conclusive evidence that the cerebellum is the primary or sole neuroanatomical site of origin.

Cerebellar transcranial direct current stimulation in neurological disease

Several studies have highlighted the therapeutic potential of transcranial direct current stimulation (tDCS) in patients with neurological diseases, including dementia, epilepsy, post-stroke dysfunctions, movement disorders, and other pathological conditions.

Because of this technique’s ability to modify cerebellar excitability without significant side effects, cerebellar tDCS is a new, interesting, and powerful tool to induce plastic modifications in the cerebellum.

In this report, we review a number of interesting studies on the application of cerebellar tDCS for various neurological conditions (ataxia, Parkinson’s disease, dystonia, essential tremor) and the possible mechanism by which the stimulation acts on the cerebellum.

Study findings indicate that cerebellar tDCS is a promising therapeutic tool in treating several neurological disorders; however, this method’s efficacy appears to be limited, given the current data.

Molecular imaging of movement disorders

Positron emission tomography measures the activity of radioactively labeled compounds which distribute and accumulate in central nervous system regions in proportion to their metabolic rate or blood flow. Specific circuits such as the dopaminergic nigrostriatal projection can be studied with ligands that bind to the pre-synaptic dopamine transporter or post-synaptic dopamine receptors (D1 and D2). Single photon emission computerized tomography (SPECT) measures the activity of similar tracers labeled with heavy radioactive species such as technetium and iodine. In essential tremor, there is cerebellar hypermetabolism and abnormal GABAergic function in premotor cortices, dentate nuclei and ventral thalami, without significant abnormalities in dopaminergic transmission. In Huntington’s disease, there is hypometabolism in the striatum, frontal and temporal cortices. Disease progression is accompanied by reduction in striatal D1 and D2 binding that correlate with trinucleotide repeat length, disease duration and severity. In dystonia, there is hypermetabolism in the basal ganglia, supplementary motor areas and cerebellum at rest. Thalamic and cerebellar hypermetabolism is seen during dystonic movements, which can be modulated by globus pallidus deep brain stimulation (DBS). Additionally, GABA-A receptor activity is reduced in motor, premotor and somatosensory cortices. In Tourette’s syndrome, there is hypermetabolism in premotor and sensorimotor cortices, as well as hypometabolism in the striatum, thalamus and limbic regions at rest. During tics, multiple areas related to cognitive, sensory and motor functions become hypermetabolic. Also, there is abnormal serotoninergic transmission in prefrontal cortices and bilateral thalami, as well as hyperactivity in the striatal dopaminergic system which can be modulated with thalamic DBS. In Parkinson’s disease (PD), there is asymmetric progressive decline in striatal dopaminergic tracer accumulation, which follows a caudal-to-rostral direction. Uptake declines prior to symptom presentation and progresses from contralateral to the most symptomatic side to bilateral, correlating with symptom severity. In progressive supranuclear palsy (PSP) and multiple system atrophy (MSA), striatal activity is symmetrically and diffusely decreased. The caudal-to-rostral pattern is lost in PSP, but could be present in MSA. In corticobasal degeneration (CBD), there is asymmetric, diffuse reduction of striatal activity, contralateral to the most symptomatic side. Additionally, there is hypometabolism in contralateral parieto-occipital and frontal cortices in PD; bilateral putamen and cerebellum in MSA; caudate, thalamus, midbrain, mesial frontal and prefrontal cortices in PSP; and contralateral cortices in CBD. Finally, cardiac sympathetic SPECT signal is decreased in PD. The capacity of molecular imaging to provide in vivo time courses of gene expression, protein synthesis, receptor and transporter binding, could facilitate the development and evaluation of novel medical, surgical and genetic therapies in movement disorders.

Deep brain stimulation for intractable tardive dystonia: Literature overview

BACKGROUND

Tardive dystonia (TD) represents a side effect of prolonged intake of dopamine receptor blocking compounds. TD can be a disabling movement disorder persisting despite available medical treatment. Deep brain stimulation (DBS) has been reported successful in this condition although the number of treated patients with TD is still limited to small clinical studies or case reports. The aim of this study was to present the systematical overview of the existing literature regarding DBS for intractable TD.

METHODS AND RESULTS

A literature search was carried out in PudMed. Clinical case series or case reports describing the patients with TD after DBS treatment were included in the present overview. Literature search revealed 19 articles reporting 59 individuals operated for TD. GPi was the target in 55 patients, while subthalamic nucleus (STN) was the target in the remaining 4. In most studies the motor part of Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) was improved by more than 80% when compared to preoperative BFMDRS scores.

CONCLUSIONS

The performed literature analysis indicates that bilateral GPi DBS is an effective treatment for disabling TD. The response of TD to bilateral GPi DBS may be very rapid and occurs within days/weeks after the procedure. The efficacy of bilateral GPi DBS in TD patients is comparable to results achieved in patients with primary generalized dystonia.

Therapeutic Perspective on Tardive Syndrome with Special Reference to Deep Brain Stimulation

Tardive syndrome (TDS) is a potentially permanent and irreversible hyperkinetic movement disorder caused by exposure to dopamine receptor blocking agents. Guidelines published by the American Academy of Neurology recommend pharmacological first-line treatment for TDS with clonazepam (level B), ginkgo biloba (level B), amantadine (level C), and tetrabenazine (level C). Recently, a class II study provided level C evidence for use of deep brain stimulation (DBS) of the globus pallidus internus (GPi) in patients with TDS. Although the precise pathogenesis of TDS remains to be elucidated, the beneficial effects of GPi-DBS in patients with TDS suggest that the disease may be a basal ganglia disorder. In addition to recent advances in understanding the pathophysiology of TDS, this article introduces the current use of DBS in the treatment of medically intractable TDS.

PET Neuroimaging: Insights on Dystonia and Tourette Syndrome and Potential Applications

Primary dystonia (pD) is a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both. Gilles de la Tourette syndrome (GTS) is a childhood-onset neuropsychiatric developmental disorder characterized by motor and phonic tics, which could progress to behavioral changes. GTS and obsessive-compulsive disorders are often seen in comorbidity, also suggesting that a possible overlap in the pathophysiological bases of these two conditions. PET techniques are of considerable value in detecting functional and molecular abnormalities in vivo, according to the adopted radioligands. For example, PET is the unique technique that allows in vivo investigation of neurotransmitter systems, providing evidence of changes in GTS or pD. For example, presynaptic and post-synaptic dopaminergic studies with PET have shown alterations compatible with dysfunction or loss of D2-receptors bearing neurons, increased synaptic dopamine levels, or both. Measures of cerebral glucose metabolism with (18)F-fluorodeoxyglucose PET ((18)F-FDG PET) are very sensitive in showing brain functional alterations as well. (18)F-FDG PET data have shown metabolic changes within the cortico-striato-pallido-thalamo-cortical and cerebello-thalamo-cortical networks, revealing possible involvement of brain circuits not limited to basal ganglia in pD and GTS. The aim of this work is to overview PET consistent neuroimaging literature on pD and GTS that has provided functional and molecular knowledge of the underlying neural dysfunction. Furthermore, we suggest potential applications of these techniques in monitoring treatments.

Changes in brain functional connectivity after chronic haloperidol in rats: a network analysis

Although the effects of haloperidol (HAL) have been extensively examined in experimental animals at the cellular and brain regional levels, the effects of prolonged HAL treatment on functional connectivity in the brain have not yet been addressed. Here we used expression of the immediate early gene zif268 as a marker of neural activity to examine changes in brain regional interactivity after 12 wk of HAL treatment in rats. zif268 expression was measured by in situ hybridization in 83 brain regions of HAL- and vehicle (VEH)-treated controls and correlations among all brain regions were computed separately for the two treatment groups. The strongest correlations in each group were used for network construction. It was found that VEH and HAL networks were equally segregated and integrated, and that both networks display small world organization. Compared to the VEH network, the HAL network showed enhanced interactivity between the dorsolateral striatum and thalamus, and between different subdivisions of the thalamus. It will be of interest to determine the extent to which the observed changes in functional connectivity may be related to dyskinesias, to changes in motivated behaviours and/or to the therapeutic effects of chronic HAL. By identifying the connectivity features of a chronic HAL network in the absence of other manipulations, the current findings may provide a reference signature pattern to be targeted in future efforts to discriminate between the neural bases of different behavioural outcomes arising from chronic HAL treatment.

Brain stimulation and functional imaging with fMRI and PET

The use of functional brain imaging techniques, including positron emission tomography (PET), single-photon emission computed tomography (SPECT), and functional magnetic resonance imaging (fMRI), has allowed for monitoring neuronal and neurochemical activities in the living human brain and identifying abnormal changes in various neurological and psychiatric diseases. Combining these methods with techniques such as deep brain stimulation (DBS) and transcranial magnetic stimulation (TMS) has greatly advanced our understanding of the effects of such treatment on brain activity at targeted regions as well as specific disease-related networks. Indeed, recent network-level analysis focusing on inter-regional covarying activities in data interpretation has unveiled several key mechanisms underlying the therapeutic effects of brain stimulation. However, non-negligible discrepancies have been reported in the literature, attributable in part to the heterogeneity of both imaging and brain stimulation techniques. This chapter summarizes recent studies that combine brain imaging and brain stimulation, and includes discussion of future direction in these lines of research.

Animal models for dystonia

Symptomatic animal models have clinical features consistent with human disorders and are often used to identify the anatomical and physiological processes involved in the expression of symptoms and to experimentally demonstrate causality where it would be infeasible in the patient population. Rodent and primate models of dystonia have identified basal ganglia abnormalities, including alterations in striatal GABAergic (ie, transmitting or secreting γ-aminobutyric acid) and dopaminergic transmission. Symptomatic animal models have also established the critical role of the cerebellum in dystonia, particularly abnormal glutamate signaling and aberrant Purkinje cell activity. Further, experiments suggest that the basal ganglia and cerebellum are nodes in an integrated network that is dysfunctional in dystonia. The knowledge gained from experiments in symptomatic animal models may serve as the foundation for the development of novel therapeutic interventions to treat dystonia. © 2013 Movement Disorder Society.

Emerging concepts in the physiological basis of dystonia

Work over the past 2 decades has led to substantial changes in our understanding of dystonia pathophysiology. Three general abnormalities appear to underlie the pathophysiological substrate. The first is a loss of inhibition. This makes sense considering that it may be responsible for the excess of movement and for the overflow phenomena seen in dystonia. A second abnormality is sensory dysfunction which is related to the mild sensory complaints in patients with focal dystonias and may be responsible for some of the motor dysfunction. Third, evidence from animal models of dystonia as well as from patients with primary dystonia has revealed significant alterations of synaptic plasticity characterized by a disruption of homeostatic plasticity, with a prevailing facilitation of synaptic potentiation, together with the loss of synaptic inhibitory processes. We speculate that during motor learning this abnormal plasticity may lead to an abnormal sensorimotor integration, leading to consolidation of abnormal motor engrams. If so, then removing this abnormal plasticity might have little immediate effect on dystonic movements because bad motor memories have already been ''learned'' and are difficult to erase. These considerations might explain the delayed clinical effects of deep brain stimulation (DBS) in patients with generalized dystonia. Current lines of research will be discussed from a network perspective. © 2013 Movement Disorder Society.

Dystonia as a network disorder: what is the role of the cerebellum?

The dystonias are a group of disorders defined by sustained or intermittent muscle contractions that result in involuntary posturing or repetitive movements. There are many different clinical manifestations and causes. Although they traditionally have been ascribed to dysfunction of the basal ganglia, recent evidence has suggested dysfunction may originate from other regions, particularly the cerebellum. This recent evidence has led to an emerging view that dystonia is a network disorder that involves multiple brain regions. The new network model for the pathogenesis of dystonia has raised many questions, particularly regarding the role of the cerebellum. For example, if dystonia may arise from cerebellar dysfunction, then why are there no cerebellar signs in dystonia? Why are focal cerebellar lesions or degenerative cerebellar disorders more commonly associated with ataxia rather than dystonia? Why is dystonia more commonly associated with basal ganglia lesions rather than cerebellar lesions? Can answers obtained from animals be extrapolated to humans? Is there any evidence that the cerebellum is not involved? Finally, what is the practical value of this new model of pathogenesis for the neuroscientist and clinician? This article explores potential answers to these questions.

Deep brain stimulation for dystonia

The few controlled studies that have been carried out have shown that bilateral internal globus pallidum stimulation is a safe and long-term effective treatment for hyperkinetic disorders. However, most recent published data on deep brain stimulation (DBS) for dystonia, applied to different targets and patients, are still mainly from uncontrolled case reports (especially for secondary dystonia). This precludes clear determination of the efficacy of this procedure and the choice of the 'good' target for the 'good' patient. We performed a literature analysis on DBS for dystonia according to the expected outcome. We separated those with good evidence of favourable outcome from those with less predictable outcome. In the former group, we review the main results for primary dystonia (generalised/focal) and highlight recent data on myoclonus-dystonia and tardive dystonia (as they share, with primary dystonia, a marked beneficial effect from pallidal stimulation with good risk/benefit ratio). In the latter group, poor or variable results have been obtained for secondary dystonia (with a focus on heredodegenerative and metabolic disorders). From this overview, the main results and limits for each subgroup of patients that may help in the selection of dystonic patients who will benefit from DBS are discussed.

Gray matter density increase in the primary sensorimotor cortex in long-term essential blepharospasm

In this study, we investigated gray matter density in essential blepharospasm (EB) patients, focusing on the duration of disease and severity of symptoms. We studied 32 patients (10 males and 22 females; age, 55.0 ± 6.5years) with EB and 48 controls (15 males and 33 females; age, 54.4 ± 10.3years) by using 3D T1-weighted magnetic resonance imaging and voxel-based morphometry. We defined an activity index (AI) that reflects the severity and duration of EB symptoms in each patient. The difference between the 2 groups was examined by statistical parametric mapping software (SPM8). After controlling for age, gray matter density increased in the bilateral primary sensorimotor cortex (S1M1) and cingulate gyrus. The gray matter density in the bilateral S1M1 was found to have a significant positive correlation with the duration of disease and a more robust correlation with AI. The correlation coefficients, after correcting for age, in the S1M1 and left cingulate gyrus were as follows: with duration, right S1M1, 0.72 (P<0.00001); left S1M1, 0.72 (P<0.00001); and left cingulate gyrus, 0.33 (not significant); and with AI, right S1M1, 0.81 (P<10(-7)); left S1M1, 0.74 (P<0.00001); and left cingulate gyrus, 0.43 (P<0.05). The increase in gray matter density in the S1M1 and cingulate gyrus might be a secondary effect caused by long-term hyperactivity in these areas instead of a predisposing factor.

The functional neuroanatomy of dystonia

Dystonia is a neurological disorder characterized by involuntary twisting movements and postures. There are many different clinical manifestations, and many different causes. The neuroanatomical substrates for dystonia are only partly understood. Although the traditional view localizes dystonia to basal ganglia circuits, there is increasing recognition that this view is inadequate for accommodating a substantial portion of available clinical and experimental evidence. A model in which several brain regions play a role in a network better accommodates the evidence. This network model accommodates neuropathological and neuroimaging evidence that dystonia may be associated with abnormalities in multiple different brain regions. It also accommodates animal studies showing that dystonic movements arise with manipulations of different brain regions. It is consistent with neurophysiological evidence suggesting defects in neural inhibitory processes, sensorimotor integration, and maladaptive plasticity. Finally, it may explain neurosurgical experience showing that targeting the basal ganglia is effective only for certain subpopulations of dystonia. Most importantly, the network model provides many new and testable hypotheses with direct relevance for new treatment strategies that go beyond the basal ganglia. This article is part of a Special Issue entitled "Advances in dystonia".

Effects of acupuncture on the brain hemodynamics

Acupuncture therapy has been applied to various psychiatric diseases and chronic pain since acupuncture stimulation might affect brain activity. From this point of view, we investigated the effects of acupuncture on autonomic nervous system and brain hemodynamics in human subjects using ECGs, EEGs and near-infrared spectroscopy (NIRS). Our previous studies reported that changes in parasympathetic nervous activity were correlated with number of de-qi sensations during acupuncture manipulation. Furthermore, these autonomic changes were correlated with EEG spectral changes. These results are consistent with the suggestion that autonomic changes induced by needle manipulation inducing specific de-qi sensations might be mediated through the central nervous system, especially through the forebrain as shown in EEG changes, and are beneficial to relieve chronic pain by inhibiting sympathetic nervous activity. The NIRS results indicated that acupuncture stimulation with de-qi sensation significantly decreased activity in the supplementary motor complex (SMC) and dorsomedial prefrontal cortex (DMPFC). Based on these results, we review that hyperactivity in the SMC is associated with dystonia and chronic pain, and that in the DMPFC is associated with various psychiatric diseases with socio-emotional disturbances such as schizophrenia, attention deficit hyperactive disorder, etc. These findings along with the previous studies suggest that acupuncture with de-qi sensation might be effective to treat the various diseases in which hyperactivity in the SMA and DMPFC is suspected of playing a role.

Chronic deep brain stimulation in patients with tardive dystonia without a history of major psychosis

Tardive dystonia usually occurs with a delay after neuroleptic exposure in patients with major psychosis. A subgroup of patients, however, is given such medication for "mild depression" or "neurasthenia." Tardive dystonia, in general, may respond favorably to pallidal deep brain stimulation (DBS). Nevertheless, it remains unclear thus far whether or not similar beneficial outcome is achieved with pallidal DBS in different subgroups of patients with tardive dystonia. Four women (mean age 59 years at surgery) underwent stereotactic pallidal DBS in the frame of an observational study. Tardive dystonia occurred secondary to medication with fluspirilene and haloperidol, and injection of long-acting depot neuroleptics prescribed for mild depression or "nervousness." Assessment included the Burke-Fahn-Marsden (BFM) scale preoperatively and at 12 months follow-up. Extended follow-up was available at a mean of 27.3 months postoperatively (range 16-36 months). There were no surgically related complications. All 4 patients experienced sustained statistically significant benefit from pallidal DBS. Mean improvement at 12 months was 77% for the BFM motor score (range, 45-91%; P = 0.043), and 84% at the last available follow-up (range, 70-91%; P = 0.03). This was paralleled by improvement of the BFM disability score. Chronic pallidal DBS in patients with tardive dystonia without a history of major psychosis provides sustained improvement which is similar to that in other subgroups of patients with tardive dystonia. This effect is stable on extended follow-up for up to 3 years.

Surgical treatment of dystonia

Surgical treatment of dystonia has experienced a tremendous change over the past decade. Whilst selective peripheral denervation is reserved for cervical dystonia refractory to botulinum toxin injections, deep brain stimulation (DBS) of the pallidum has gained a wide scope and presents an elementary column in the treatment of medically refractory patients, nowadays. There is consensus that idiopathic generalized, cervical and segmental dystonia are good indications for DBS, although there is still a paucity of studies providing high-level data according to EBM criteria. Efficacy is maintained on longterm. Several other forms of primary dystonia are still under investigation but it appears that patients with Meige syndrome and myoclonus-dystonia gain also marked benefit. Study of the outcome in secondary dystonia disorders is more complex, in general, but patients with tardive dystonia gain similar improvement than patients with idiopathic dystonia. Overall, the risk profile of pallidal DBS is quite low, and it has been shown to be cognitively safe. The effect of pallidal DBS on non-dystonic extremities has not received much attention, albeit there are hints for a pro-akinetic mechanism. Several questions remain to be solved including optimal programming of stimulation settings, battery drain with high stimulation energies and the elucidation of the mechanisms of DBS in dystonia.

Hereditary dystonia as a neurodevelopmental circuit disorder: Evidence from neuroimaging

Primary dystonia has traditionally been viewed as a basal ganglia disorder, but recent studies suggest that the cerebellum plays a crucial role in the disease. Primary dystonia is associated with several genotypes. Among those, DYT1 and DYT6 are inherited in autosomal dominant fashion with reduced penetrance. Extensive structural and functional imaging studies have been performed on manifesting and non-manifesting carriers of these mutations. The results suggest that primary dystonia can be viewed as a neurodevelopmental circuit disorder, involving the cortico-striato-pallido-thalamo-cortical and cerebello-thalamo-cortical pathways. Anatomical disruption of the cerebellar outflow is found in non-manifesting and manifesting mutation carriers, and a second downstream disruption in thalamo-cortical projections appears clinically protective in non-manifesting carriers. The microstructural deficits in cerebellar outflow are linked to an abnormally elevated sensorimotor network (NMRP) in dystonia patients. Abnormal expression of this network is reduced by successful treatment with deep brain stimulation. This article is part of a Special Issue entitled "Advances in dystonia".

Regional cerebral blood flow changes induced by deep brain stimulation in secondary dystonia

PURPOSE

The purpose of the present study is to investigate the effect of deep brain stimulation (DBS) on regional cerebral blood flow (rCBF) in cases of secondary dystonia as well as to correlate the rCBF changes with clinical outcomes.

METHODS

Six patients with medically intractable secondary dystonia who underwent DBS surgery were included in this study. Burke-Fahn-Mardsen Dystonia Rating Scale (BFMDRS) was used for the assessment of dystonia, before and after surgery. Single photon emission computed tomography (SPECT) of the brain was performed postoperatively in the two stimulation states (ON-DBS and OFF-DBS) and the changes of rCBF in the three following brain regions of interest (ROIs): primary motor cortex, premotor and supplementary motor cortex, and prefrontal cortex were evaluated.

RESULTS

Two patients exhibited excellent response to DBS, two patients got moderate benefit after the procedure, and in two patients, no clinical improvement was achieved. A mean improvement of 49.1% (0-90.7%) in BFMDRS total scores was found postoperatively. Brain SPECT data analysis revealed an overall decrease in rCBF in the investigated ROIs, during the ON-DBS state. Clinical improvement was significantly correlated with the observed decrease in rCBF in the presence of DBS.

CONCLUSIONS

When conservative treatment fails to relieve severely disabled patients suffering from secondary dystonia, DBS may be a promising therapeutic alternative. Moreover, this study indicates a putative role of brain SPECT imaging as a postoperative indicator of clinical responsiveness to DBS.

PET functional imaging of deep brain stimulation in movement disorders and psychiatry

Deep brain stimulation (DBS) represents a major advance in the treatment of various severe movement disorders or neuropsychiatric diseases. Our understanding of the mechanism of action of this surgical treatment has greatly benefited from functional imaging studies. Most of these studies have been conducted in patients with Parkinson's disease (PD) treated by bilateral subthalamic nucleus (STN) stimulation. These studies have notably underlined the fact that STN stimulation influences motor, limbic, or associative cortical-subcortical loops in various (sometimes contradictory) ways. We present an up-to-date review of the information provided by functional imaging studies in surgery for PD, dystonia, tremor, as well as in psychiatric disorders such as depression or obsessive-compulsive disorder. On the basis of this information, proposed mechanisms of action of DBS are discussed, as well as the need for additional approaches such as improved anatomical localization of the contact used for stimulation or a better understanding of the electrical distribution around the electrode.