Increased activation of frontal areas during arm movement in idiopathic torsion dystonia

Sensorimotor Integration and Pain Perception: Mechanisms Integrating Nociceptive Processing. A Systematic Review and ALE-Meta Analysis

Pain treatment services and clinical indicators of pain chronicity focus on afferent nociceptive projections and psychological markers of pain perception with little focus on motor processes. Research supports a strong role for the motor system both in terms of pain related disability and in descending pain modulation. However, there is little understanding of the neurological regions implicated in pain-motor interactions and how the motor and sensory systems interact under conditions of pain. We performed an ALE meta-analysis on two clinical cohorts with atypical sensory and motor processes under conditions of pain and no pain. Persons with sensory altered processing (SAP) and no pain presented with greater activity in the precentral and supplementary motor area relative to persons with self-reported pain. In persons with motor altered processing (MAP), there appeared to be a suppression of activity in key pain regions such as the insula, thalamus, and postcentral gyrus. As such, activation within the motor system may play a critical role in dampening pain symptoms in persons with SAP, and in suppressing activity in key pain regions of the brain in persons with MAP. Future research endeavors should focus on understanding how sensory and motor processes interact both to understand disability and discover new treatment avenues.

Cortical activation and motor body representations in a patient with subacute sclerosing panencephalitis

The current neuroimaging study investigated the sensorimotor maps during hand, feet and lips movements at one year after diagnosis of of subacute sclerosing panencephalitis (SSPE) in a 17 years-old patient. A lesion prediction algorithm showed that the posterior thalamic radiations, the splenium of the corpus callosum, the posterior and superior corona radiate, and the cingolum, showed a high lesion probability. Comparing the fMRI activations of the left and right hemisphere, we found that the representation of the left hand movement was more inferior/anterior and less represented than the representation of the right one; and the representation of the right foot movement was more superior, less represented than the representation of the left one and poorly activated at the predefined statistical threshold. The fMRI results are in line with the clinical report, describing an asymmetrical distribution of the periodic stereotyped myoclonic jerks, which mainly occurred for the left arm/hand and for the right leg/foot. This is the first fMRI study investigating the representation of the body parts in patients with SSPE. Results show that in SSPE the hyper-stimulation of the motor system (dedicated to the arm/hand and leg/foot more involved by the occurrence of the jerks) is accompanied by an under-activation of the corresponding motor representations in coincidence with voluntary movements.

Imaging Insights of Isolated Idiopathic Dystonia: Voxel-Based Morphometry and Activation Likelihood Estimation Studies

The understanding of brain structural abnormalities across different clinical forms of dystonia and their contribution to clinical characteristics remains unclear. The objective of this study is to investigate shared and specific gray matter volume (GMV) abnormalities in various forms of isolated idiopathic dystonia. We collected imaging data from 73 isolated idiopathic dystonia patients and matched them with healthy controls to explore the GMV alterations in patients and their correlations with clinical characteristics using the voxel-based morphometry (VBM) technique. In addition, we conducted an activation likelihood estimation (ALE) meta-analysis of previous VBM studies. Our study demonstrated widespread morphometry alterations in patients with idiopathic dystonia. Multiple systems were affected, which mainly included basal ganglia, sensorimotor, executive control, and visual networks. As the result of the ALE meta-analysis, a convergent cluster with increased GMV was found in the left globus pallidus. In subgroup VBM analyses, decreased putamen GMV was observed in all clinic forms, while the increased GMV was observed in parahippocampal, lingual, and temporal gyrus. GD demonstrated the most extensive GMV abnormalities in cortical regions, and the aberrant GMV of the posterior cerebellar lobe was prominent in CD. Moreover, trends of increased GMV regions of the left precuneus and right superior frontal gyrus were demonstrated in the moderate-outcome group compared with the superior-outcome group. Results of our study indicated shared pathophysiology of the disease-centered on the dysfunction of the basal ganglia-thalamo-cortical circuit, impairing sensorimotor integration, high-level motor execution, and cognition of patients. Dysfunction of the cerebello-thalamo-cortical circuit could also be involved in CD especially. Finally, the frontal-parietal pathway may act as a potential marker for predicting treatment outcomes such as deep brain stimulation.

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.

Morphological Abnormalities in the Basal Ganglia of Dystonia Patients

OBJECTIVE

The pathophysiology of dystonia is poorly understood. As opposed to secondary forms of dystonia, primary dystonia has long been believed to lack any neuroanatomical substrate. During trajectory planning for DBS, however, conspicuous T2-hyperinstensive signal alterations (SA) were registered within the target region, even in young patients, where ischemia is rare.

METHODS

Fifty MRIs of primary dystonia patients scheduled for DBS were analyzed. Total basal ganglia (BG) volumes, as well as proportionate SA volumes, were measured and compared to 50 age-matched control patients.

RESULTS

There was a 10-fold preponderance of percentaged SA within the globus pallidus (GP) in dystonia patients. The greatest disparity was in young patients <25 years. Also, total BG volume differences were observed with larger GP and markedly smaller putamen and caudate in the dystonia group.

CONCLUSIONS

BG morphology in primary dystonia differed from a control population. Volume reductions of the putamen and caudate may reflect functional degeneration, while volume increases of the GP may indicate overactivity. T2-hyperintensive SA in the GP of young primary dystonia patients, where microvascular lesions are highly unlikely, are striking. Their pathogenic role remains unclear.

Cerebral blood flow in dystonia due to pantothenate kinase-associated neurodegeneration

BACKGROUND AND PURPOSE

The aim of this study was to look for deviations of cerebral perfusion in patients suffering from pantothenate kinase-associated neurodegeneration, where the globus pallidus is affected by severe accumulation of iron.

MATERIAL AND METHODS

Under resting conditions, cerebral blood flow was measured by the magnetic resonance imaging technique of arterial spin labelling in cortical areas and basal ganglia in eight pantothenate kinase-associated neurodegeneration patients and 14 healthy age-matched control subjects and correlated to T2* time of these areas and - in patients - to clinical parameters.

RESULTS

Despite highly significant differences of T2* time of the globus pallidus (20 vs 39 ms, p < 0.001), perfusion values of this nucleus were nearly identical in both groups (32 ± 3.3 vs 31 ± 4.0 ml/min/100 g) as well as in total brain gray matter (both 62 ± 6.7 resp. ±10.3 ml/min/100 g), putamen (41 ± 5.4 vs 40 ± 6.1 ml/min/100 g), in selected cortical regions, and the cerebellum. Correlations between perfusion and T2* time to clinical data did not reach significance (p > 0.05).

CONCLUSION

The absence of any obvious deviations of perfusion in the group of patients during a resting condition does not support the view that (non-functional) vascular pathology is a major pathogenic factor in pantothenate kinase-associated neurodegeneration in the younger age group. The findings underline the value of the arterial spin technique to measure cerebral blood flow in areas of disturbed susceptibility.

Neuroimaging Applications in Dystonia

Dystonia is a neurological disorder characterized by involuntary, repetitive movements. Although the precise mechanisms of dystonia development remain unknown, the diversity of its clinical phenotypes is thought to be associated with multifactorial pathophysiology, which is linked not only to alterations of brain organization, but also environmental stressors and gene mutations. This chapter will present an overview of the pathophysiology of isolated dystonia through the lens of applications of major neuroimaging methodologies, with links to genetics and environmental factors that play a prominent role in symptom manifestation.

Loss of inhibition in sensorimotor networks in focal hand dystonia

Objective

To investigate GABA-ergic receptor density and associated brain functional and grey matter changes in focal hand dystonia (FHD).

Methods

18 patients with FHD of the right hand and 18 age and gender matched healthy volunteers (HV) participated in this study. We measured the density of GABA-A receptors using [¹¹C] Flumazenil and perfusion using [¹⁵O] H₂O. Anatomical images were also used to measure grey matter volume with voxel-based morphometry (VBM).

Results

In FHD patients compared to HV, the vermis VI of the right cerebellum and the left sensorimotor cortex had a decrease of Flumazenil binding potential (FMZ-BP), whereas the striatum and the lateral cerebellum did not show significant change. Bilateral inferior prefrontal cortex had increased FMZ-BP and an increase of perfusion, which correlated negatively with disease duration. Only the left sensorimotor cortex showed a decrease of grey matter volume.

Interpretation

Impairments of GABAergic neurotransmission in the cerebellum and the sensorimotor cortical areas could explain different aspects of loss of inhibitory control in FHD, the former being involved in maladaptive plasticity, the latter in surround inhibition. Reorganization of the inferior prefrontal cortices, part of the associative network, might be compensatory for the loss of inhibitory control in sensorimotor circuits. These findings suggest that cerebellar and cerebral GABAergic abnormalities could play a role in the functional imbalance of striato-cerebello-cortical loops in dystonia.

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We tested GABAergic deficiency to explain inhibitory control loss in focal dystonia.

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The right cerebellar vermis and left sensorimotor cortex had GABAergic deficiencies.

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Bilateral prefrontal cortex had an increase of GABAergic potential and activity.

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Prefrontal changes correlated with cerebellar deficiency and disease duration.

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We highlighted the importance of the cerebellum for the pathophysiology of dystonia.

Altered sensorimotor activation patterns in idiopathic dystonia-an activation likelihood estimation meta-analysis of functional brain imaging studies

Dystonia is characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements or postures. Functional neuroimaging studies have yielded abnormal task‐related sensorimotor activation in dystonia, but the results appear to be rather variable across studies. Further, study size was usually small including different types of dystonia. Here we performed an activation likelihood estimation (ALE) meta‐analysis of functional neuroimaging studies in patients with primary dystonia to test for convergence of dystonia‐related alterations in task‐related activity across studies. Activation likelihood estimates were based on previously reported regional maxima of task‐related increases or decreases in dystonia patients compared to healthy controls. The meta‐analyses encompassed data from 179 patients with dystonia reported in 18 functional neuroimaging studies using a range of sensorimotor tasks. Patients with dystonia showed bilateral increases in task‐related activation in the parietal operculum and ventral postcentral gyrus as well as right middle temporal gyrus. Decreases in task‐related activation converged in left supplementary motor area and left postcentral gyrus, right superior temporal gyrus and dorsal midbrain. Apart from the midbrain cluster, all between‐group differences in task‐related activity were retrieved in a sub‐analysis including only the 14 studies on patients with focal dystonia. For focal dystonia, an additional cluster of increased sensorimotor activation emerged in the caudal cingulate motor zone. The results show that dystonia is consistently associated with abnormal somatosensory processing in the primary and secondary somatosensory cortex along with abnormal sensorimotor activation of mesial premotor and right lateral temporal cortex. Hum Brain Mapp 37:547–557, 2016. © 2015 Wiley Periodicals, Inc.

Focal dystonia and the Sensory-Motor Integrative Loop for Enacting (SMILE)

Performing accurate movements requires preparation, execution, and monitoring mechanisms. The first two are coded by the motor system, the latter by the sensory system. To provide an adaptive neural basis to overt behaviors, motor and sensory information has to be properly integrated in a reciprocal feedback loop. Abnormalities in this sensory-motor loop are involved in movement disorders such as focal dystonia, a hyperkinetic alteration affecting only a specific body part and characterized by sensory and motor deficits in the absence of basic motor impairments. Despite the fundamental impact of sensory-motor integration mechanisms on daily life, the general principles of healthy and pathological anatomic–functional organization of sensory-motor integration remain to be clarified. Based on the available data from experimental psychology, neurophysiology, and neuroimaging, we propose a bio-computational model of sensory-motor integration: the Sensory-Motor Integrative Loop for Enacting (SMILE). Aiming at direct therapeutic implementations and with the final target of implementing novel intervention protocols for motor rehabilitation, our main goal is to provide the information necessary for further validating the SMILE model. By translating neuroscientific hypotheses into empirical investigations and clinically relevant questions, the prediction based on the SMILE model can be further extended to other pathological conditions characterized by impaired sensory-motor integration.

The anatomical basis of dystonia: current view using neuroimaging

This review will consider the knowledge that neuroimaging studies have provided to the understanding of the anatomy of dystonia. Major advances have occurred in the use of neuroimaging for dystonia in the past 2 decades. At present, the most developed imaging approaches include whole-brain or region-specific studies of structural or diffusion changes, functional imaging using fMRI or positron emission tomography (PET), and metabolic imaging using fluorodeoxyglucose PET. These techniques have provided evidence that regions other than the basal ganglia are involved in dystonia. In particular, there is increasing evidence that primary dystonia can be viewed as a circuit disorder, involving the basal ganglia-thalamo-cortical and cerebello-thalamo-cortical pathways. This suggests that a better understanding of the dysfunction in each region in the network and their interactions are important topics to address. Current views of interpretation of imaging data as cause or consequence of dystonia, and the postmortem correlates of imaging data are presented. The application of imaging as a tool to monitor therapy and its use as an outcome measure will be discussed. © 2013 Movement Disorder Society.

Task-free functional MRI in cervical dystonia reveals multi-network changes that partially normalize with botulinum toxin

Cervical dystonia is characterized by involuntary, abnormal movements and postures of the head and neck. Current views on its pathophysiology, such as faulty sensorimotor integration and impaired motor planning, are largely based on studies of focal hand dystonia. Using resting state fMRI, we explored whether cervical dystonia patients have altered functional brain connectivity compared to healthy controls, by investigating 10 resting state networks. Scans were repeated immediately before and some weeks after botulinum toxin injections to see whether connectivity abnormalities were restored. We here show that cervical dystonia patients have reduced connectivity in selected regions of the prefrontal cortex, premotor cortex and superior parietal lobule within a distributed network that comprises the premotor cortex, supplementary motor area, primary sensorimotor cortex, and secondary somatosensory cortex (sensorimotor network). With regard to a network originating from the occipital cortex (primary visual network), selected regions in the prefrontal and premotor cortex, superior parietal lobule, and middle temporal gyrus areas have reduced connectivity. In selected regions of the prefrontal, premotor, primary motor and early visual cortex increased connectivity was found within a network that comprises the prefrontal cortex including the anterior cingulate cortex and parietal cortex (executive control network). Botulinum toxin treatment resulted in a partial restoration of connectivity abnormalities in the sensorimotor and primary visual network. These findings demonstrate the involvement of multiple neural networks in cervical dystonia. The reduced connectivity within the sensorimotor and primary visual networks may provide the neural substrate to expect defective motor planning and disturbed spatial cognition. Increased connectivity within the executive control network suggests excessive attentional control and while this may be a primary trait, perhaps contributing to abnormal motor control, this may alternatively serve a compensatory function in order to reduce the consequences of the motor planning defect inflicted by the other network abnormalities.

SGCE mutations cause psychiatric disorders: clinical and genetic characterization

Myoclonus dystonia syndrome is a childhood onset hyperkinetic movement disorder characterized by predominant alcohol responsive upper body myoclonus and dystonia. A proportion of cases are due to mutations in the maternally imprinted SGCE gene. Previous studies have suggested that patients with SGCE mutations may have an increased rate of psychiatric disorders. We established a cohort of patients with myoclonus dystonia syndrome and SGCE mutations to determine the extent to which psychiatric disorders form part of the disease phenotype. In all, 89 patients with clinically suspected myoclonus dystonia syndrome were recruited from the UK and Ireland. SGCE was analysed using direct sequencing and for copy number variants. In those patients where no mutation was found TOR1A (GAG deletion), GCH1, THAP1 and NKX2-1 were also sequenced. SGCE mutation positive cases were systematically assessed using standardized psychiatric interviews and questionnaires and compared with a disability-matched control group of patients with alcohol responsive tremor. Nineteen (21%) probands had a SGCE mutation, five of which were novel. Recruitment of family members increased the affected SGCE mutation positive group to 27 of whom 21 (77%) had psychiatric symptoms. Obsessive-compulsive disorder was eight times more likely (P < 0.001) in mutation positive cases, compulsivity being the predominant feature (P < 0.001). Generalized anxiety disorder (P = 0.003) and alcohol dependence (P = 0.02) were five times more likely in mutation positive cases than tremor controls. SGCE mutations are associated with a specific psychiatric phenotype consisting of compulsivity, anxiety and alcoholism in addition to the characteristic motor phenotype. SGCE mutations are likely to have a pleiotropic effect in causing both motor and specific psychiatric symptoms.

Striatal microcircuitry and movement disorders

The basal ganglia network serves to integrate information about context, actions, and outcomes to shape the behavior of an animal based on its past experience. Clinically, the basal ganglia receive the most attention for their role in movement disorders. Recent advances in technology have opened new avenues of research into the structure and function of basal ganglia circuits. One emerging theme is the importance of GABAergic interneurons in coordinating and regulating network function. Here, we discuss evidence that changes in striatal GABAergic microcircuits contribute to basal ganglia dysfunction in several movement disorders. Because interneurons are genetically and neurochemically unique from striatal projection neurons, they may provide promising therapeutic targets for the treatment of a variety of striatal-based disorders.

Disentangling motor execution from motor imagery with the phantom limb

Amputees can move their phantom limb at will. These 'movements without movements' have generally been considered as motor imagery rather than motor execution, but amputees can in fact perform both executed and imagined movements with their phantom and they report distinct perceptions during each task. Behavioural evidence for this dual ability comes from the fact that executed movements are associated with stump muscle contractions whereas imagined movements are not, and that phantom executed movements are slower than intact hand executed movements whereas the speed of imagined movements is identical for both hands. Since neither execution nor imagination produces any visible movement, we hypothesized that the perceptual difference between these two motor tasks relies on the activation of distinct cerebral networks. Using functional magnetic resonance imaging and changes in functional connectivity (dynamic causal modelling), we examined the activity associated with imagined and executed movements of the intact and phantom hands of 14 upper-limb amputees. Distinct but partially overlapping cerebral networks were active during both executed and imagined phantom limb movements (both performed at the same speed). A region of interest analysis revealed a 'switch' between execution and imagination; during execution there was more activity in the primary somatosensory cortex, the primary motor cortex and the anterior lobe of the cerebellum, while during imagination there was more activity in the parietal and occipital lobes, and the posterior lobe of the cerebellum. In overlapping areas, task-related differences were detected in the location of activation peaks. The dynamic causal modelling analysis further confirmed the presence of a clear neurophysiological distinction between imagination and execution, as motor imagery and motor execution had opposite effects on the supplementary motor area-primary motor cortex network. This is the first imaging evidence that the neurophysiological network activated during phantom limb movements is similar to that of executed movements of intact limbs and differs from the phantom limb imagination network. The dual ability of amputees to execute and imagine movements of their phantom limb and the fact that these two tasks activate distinct cortical networks are important factors to consider when designing rehabilitation programmes for the treatment of phantom limb pain.

Abnormal activation of the motor cortical network in idiopathic scoliosis demonstrated by functional MRI

The aetiology of idiopathic scoliosis (IS) remains unknown, but there is growing support for the possibility of an underlying neurological disorder. Functional magnetic resonance imaging (fMRI) can characterize the abnormal activation of the sensorimotor brain network in movement disorders and could provide further insights into the neuropathogenesis of IS. Twenty subjects were included in the study; 10 adolescents with IS (mean age of 15.2, 8 girls and 2 boys) and 10 age-matched healthy controls. The average Cobb angle of the primary curve in the IS patients was 35° (range 27°-55°). All participants underwent a block-design fMRI experiment in a 1.5-Tesla MRI scanner to explore cortical activation following a simple motor task. Rest periods alternated with activation periods during which participants were required to open and close their hand at an internally paced rate of approximately 1 Hz. Data were analyzed with Statistical Parametric Mapping (SPM5) including age, sex and laterality as nuisance variables to minimise the presence of bias in the results. Compared to controls, IS patients showed significant increases in blood oxygenation level dependent (BOLD) activity in contralateral supplementary motor area when performing the motor task with either hand. No significant differences were observed when testing between groups in the functional activation in the primary motor cortex, premotor cortex and somatosensory cortex. Additionally, the IS group showed a greater interhemispheric asymmetry index than the control group (0.30 vs. 0.13, p < 0.001). This study demonstrates an abnormal pattern of brain activation in secondary motor areas during movement execution in patients with IS. These findings support the hypothesis that a sensorimotor integration disorder underlies the pathogenesis of IS.

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".

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.

Increased sensorimotor network activity in DYT1 dystonia: a functional imaging study

Neurophysiological studies have provided evidence of primary motor cortex hyperexcitability in primary dystonia, but several functional imaging studies suggest otherwise. To address this issue, we measured sensorimotor activation at both the regional and network levels in carriers of the DYT1 dystonia mutation and in control subjects. We used (15)Oxygen-labelled water and positron emission tomography to scan nine manifesting DYT1 carriers, 10 non-manifesting DYT1 carriers and 12 age-matched controls while they performed a kinematically controlled motor task; they were also scanned in a non-motor audio-visual control condition. Within- and between-group contrasts were analysed with statistical parametric mapping. For network analysis, we first identified a normal motor-related activation pattern in a set of 39 motor and audio-visual scans acquired in an independent cohort of 18 healthy volunteer subjects. The expression of this pattern was prospectively quantified in the motor and control scans acquired in each of the gene carriers and controls. Network values for the three groups were compared with ANOVA and post hoc contrasts. Voxel-wise comparison of DYT1 carriers and controls revealed abnormally increased motor activation responses in the former group (P < 0.05, corrected; statistical parametric mapping), localized to the sensorimotor cortex, dorsal premotor cortex, supplementary motor area and the inferior parietal cortex. Network analysis of the normative derivation cohort revealed a significant normal motor-related activation pattern topography (P < 0.0001) characterized by covarying neural activity in the sensorimotor cortex, dorsal premotor cortex, supplementary motor area and cerebellum. In the study cohort, normal motor-related activation pattern expression measured during movement was abnormally elevated in the manifesting gene carriers (P < 0.001) but not in their non-manifesting counterparts. In contrast, in the non-motor control condition, abnormal increases in network activity were present in both groups of gene carriers (P < 0.001). In this condition, normal motor-related activation pattern expression in non-manifesting carriers was greater than in controls, but lower than in affected carriers. In the latter group, measures of normal motor-related activation pattern expression in the audio-visual condition correlated with independent dystonia clinical ratings (r = 0.70, P = 0.04). These findings confirm that overexcitability of the sensorimotor system is a robust feature of dystonia. The presence of elevated normal motor-related activation pattern expression in the non-motor condition suggests that abnormal integration of audio-visual input with sensorimotor network activity is an important trait feature of this disorder. Lastly, quantification of normal motor-related activation pattern expression in individual cases may have utility as an objective descriptor of therapeutic response in trials of new treatments for dystonia and related disorders.

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.

Impairment of bidirectional synaptic plasticity in the striatum of a mouse model of DYT1 dystonia: role of endogenous acetylcholine

DYT1 dystonia is a severe form of inherited dystonia, characterized by involuntary twisting movements and abnormal postures. It is linked to a deletion in the dyt1 gene, resulting in a mutated form of the protein torsinA. The penetrance for dystonia is incomplete, but both clinically affected and non-manifesting carriers of the DYT1 mutation exhibit impaired motor learning and evidence of altered motor plasticity. Here, we characterized striatal glutamatergic synaptic plasticity in transgenic mice expressing either the normal human torsinA or its mutant form, in comparison to non-transgenic (NT) control mice. Medium spiny neurons recorded from both NT and normal human torsinA mice exhibited normal long-term depression (LTD), whereas in mutant human torsinA littermates LTD could not be elicited. In addition, although long-term potentiation (LTP) could be induced in all the mice, it was greater in magnitude in mutant human torsinA mice. Low-frequency stimulation (LFS) can revert potentiated synapses to resting levels, a phenomenon termed synaptic depotentiation. LFS induced synaptic depotentiation (SD) both in NT and normal human torsinA mice, but not in mutant human torsinA mice. Since anti-cholinergic drugs are an effective medical therapeutic option for the treatment of human dystonia, we reasoned that an excess in endogenous acetylcholine could underlie the synaptic plasticity impairment. Indeed, both LTD and SD were rescued in mutant human torsinA mice either by lowering endogenous acetylcholine levels or by antagonizing muscarinic M1 receptors. The presence of an enhanced acetylcholine tone was confirmed by the observation that acetylcholinesterase activity was significantly increased in the striatum of mutant human torsinA mice, as compared with both normal human torsinA and NT littermates. Moreover, we found similar alterations of synaptic plasticity in muscarinic M2/M4 receptor knockout mice, in which an increased striatal acetylcholine level has been documented. The loss of LTD and SD on one hand, and the increase in LTP on the other, demonstrate that a 'loss of inhibition' characterizes the impairment of synaptic plasticity in this model of DYT1 dystonia. More importantly, our results indicate that an unbalanced cholinergic transmission plays a pivotal role in these alterations, providing a clue to understand the ability of anticholinergic agents to restore motor deficits in dystonia.

Globus pallidus stimulation reduces frontal hyperactivity in tardive dystonia

Tardive dystonia (TD) is a disabling disorder induced by neuroleptics. Internal globus pallidus (GPi) stimulation can dramatically improve TD. The present positron emission tomography and H(2)(15)O study aimed to characterize the abnormalities of brain activation of TD and the impact of GPi stimulation on these abnormalities in five TD patients treated with GPi stimulation and eight controls. Changes of regional cerebral blood flow (rCBF) were determined: (i) at rest; (ii) when moving a joystick with the right hand in three freely chosen directions in on and off bilateral GPi stimulation. A significant increase of rCBF was found in TD patients in off-stimulation condition compared to controls: (1) during motor execution in the prefrontal, premotor lateral, and anterior cingulate cortex; (2) at rest, in the prefrontal and anterior cingulate cortex and the cerebellum. Internal globus pallidus stimulation led to a reduction of rCBF (1) during motor execution, in the primary motor and prefrontal cortex and the cerebellum; (2) at rest, in the primary motor and anterior cingulate cortex and supplementary motor area. The results are as follows: (1) TD is related to an excess of brain activity notably in the prefrontal and premotor areas; (2) GPi stimulation reduces the activation of motor, premotor, and prefrontal cortex as well as cerebellum.

Voxel based morphometry reveals specific gray matter changes in primary dystonia

The present study assessed patterns of brain tissue alterations in different types of primary dystonia using voxel-based morphometry (VBM). Nine patients with primary generalized dystonia (GD), 11 patients with primary cervical dystonia (CD), and 11 patients with primary focal hand dystonia (FHD) as well as 31 age and gender-matched controls were included. When compared with healthy controls, patients with primary dystonia (n=31) showed gray matter volume increase bilaterally in the globus pallidus internus, nucleus accumbens, prefrontal cortex, as well as unilaterally in the left inferior parietal lobe. This is the first study using VBM in patients with different types of primary dystonia, showing a common pattern of gray matter changes.

Changed patterns of cerebral activation related to clinically normal hand movement in cervical dystonia

OBJECTIVES

The relief of cervical dystonia by sensory tricks points at complex sensorimotor interaction. The relation between such stimulus-induced normalization of posture and parietal activation [Naumann M, Magyar-Lehmann S, Reiners K, Erbguth F, Leenders KL. Sensory tricks in cervical dystonia: perceptual dysbalance of parietal cortex modulates frontal motor programming. Ann Neurol 2000;47:322-8] further supports the idea of disturbed higher-order motor control and suggests that the organization of movement is affected beyond the level of a local output channel. Dysbalance beyond a restricted output channel is also supported by the spread of focal dystonia to adjacent body parts. In this fMRI study, we aimed to determine whether cervical dystonia patients have indeed different patterns of cerebral activation during clinically normal hand performance.

PATIENTS AND METHODS

By means of statistical parametric mapping (SPM) of 3T fMRI results, task-related cerebral activations measured in eight cervical dystonia patients were compared to data of nine healthy volunteers.

RESULTS

Compared to controls, the patient group showed a relative reduction of activations in bilateral parietal, left premotor and cingulate cortex regions during imagining of movement, while activation of right (ipsilateral) putamen, insula and cingulate cortex was impaired during movement execution.

CONCLUSION

Cervical dystonia appears to concern a general disorganization of cerebral motor control, which indicates a pre-dystonic state of clinically normal hand movements. The latter may imply an increased vulnerability for deteriorating triggers such as minor accidents.

Abnormal surface EMG during clinically normal wrist movement in cervical dystonia

We investigated whether patients with cervical dystonia (CD) have abnormal muscle activation in non-dystonic body parts. Eight healthy controls and eight CD patients performed a flexion-extension movement of the right wrist. Movement execution was recorded by surface electromyography (EMG) from forearm muscles. Although patients had no complaints concerning wrist movement and had no apparent difficulty in executing the task, they demonstrated lower mean EMG amplitude (flexor: 0.32 mV and extensor: 0.61 mV) than controls (flexor: 0.67 mV; P = 0.021 and extensor: 1.18 mV; P = 0.068; borderline significant). Mean extensor muscle contraction was prolonged in patients (1860 ms) compared with controls (1334 ms; P = 0.026). Variation in mean EMG amplitude over movements tended to be higher in patients (flexor: 43% and extensor: 35%) than controls (flexor: 34%; P = 0.072 and extensor: 26%; P = 0.073). These results suggest that CD patients also have abnormal muscle activation in non-dystonic body parts at a subclinical level. This would support the concept that in dystonia, non-dystonic limbs are in a 'pre-dystonic state'.

GABAergic circuits in the basal ganglia and movement disorders

GABA is the major inhibitory neurotransmitter in the basal ganglia, and GABAergic pathways dominate information processing in most areas of these structures. It is therefore not surprising that abnormalities of GABAergic transmission are key elements in pathophysiologic models of movement disorders involving the basal ganglia. These include hypokinetic diseases such as Parkinson's disease, and hyperkinetic diseases, such as Huntington's disease or hemiballism. In this chapter, we will briefly review the major anatomic features of the GABAergic pathways in the basal ganglia, and then describe in greater detail the changes of GABAergic transmission, which are known to occur in movement disorders.

Cerebral activation during motor imagery in complex regional pain syndrome type 1 with dystonia

The pathogenesis of dystonia in Complex Regional Pain Syndrome type 1 (CRPS-1) is unclear. In primary dystonia, functional magnetic resonance imaging (fMRI) has revealed changes in cerebral networks during execution of movement. The aim of this study was to determine cerebral network function in CRPS-1 patients with dystonic postures. Cerebral processing related to both execution and imagining of hand movements in patients and controls was assessed with fMRI. Eight CRPS-1 patients with dystonic postures of the right upper extremity and 17 age-matched healthy controls were studied. Compared with controls, imaginary movement of the affected hand in patients showed reduced activation ipsilaterally in the premotor and adjacent prefrontal cortex, and in a cluster comprising frontal operculum, the anterior part of the insular cortex and the superior temporal gyrus. Contralaterally, reduced activation was seen in the inferior parietal and adjacent primary sensory cortex. There were no differences between patients and controls when they executed movements, nor when they imagined moving their unaffected hand. The altered cerebral activation pattern in patients with CRPS-1 linked dystonia most likely reflects an interface between pain-associated circuitry and higher order motor control, which points at a specific mechanistic pathophysiology of this type of dystonia.

Abnormal plasticity of the sensorimotor cortex to slow repetitive transcranial magnetic stimulation in patients with writer's cramp

Previous studies demonstrated functional abnormalities in the somatosensory system, including a distorted functional organization of the somatosensory cortex (S1) in patients with writer's cramp. We tested the hypothesis that these functional alterations render S1 of these patients more susceptible to the "inhibitory" effects of subthreshold 1 Hz repetitive transcranial magnetic stimulation (rTMS) given to S1. Seven patients with writer's cramp and eight healthy subjects were studied. Patients also received rTMS to the motor cortex hand area (M1). As an outcome measure, short-latency afferent inhibition (SAI) was tested. SAI was studied in the relaxed first dorsal interosseous muscle using conditioning electrical stimulation of the index finger and TMS pulses over the contralateral M1. Baseline SAI did not differ between groups. S1 but not M1 rTMS reduced SAI in patients. rTMS had no effects on SAI in healthy subjects. Because SAI is mediated predominantly at a cortical level in the sensorimotor cortex, we conclude that there is an abnormal responsiveness of this area to 1 Hz rTMS in writer's cramp, which may represent a trait toward maladaptive plasticity in the sensorimotor system in these patients.

Alterations in CNS activity induced by botulinum toxin treatment in spasmodic dysphonia: an H215O PET study

Speech-related changes in regional cerebral blood flow (rCBF) were measured using H(2)(15)O positron-emission tomography in 9 adults with adductor spasmodic dysphonia (ADSD) before and after botulinum toxin (BTX) injection and 10 age- and gender-matched volunteers without neurological disorders. Scans were acquired at rest and during production of continuous narrative speech and whispered speech. Speech was recorded during scan acquisition for offline quantification of voice breaks, pitch breaks, and percentage aperiodicity to assess correlations between treatment-related changes in rCBF and clinical improvement. Results demonstrated that speech-related responses in heteromodal sensory areas were significantly reduced in persons with ADSD, compared with volunteers, before the administration of BTX. Three to 4 weeks after BTX injection, speech-related responses were significantly augmented in these regions and in left hemisphere motor areas commonly associated with oral-laryngeal motor control. This pattern of responses was most strongly correlated with the objective measures of clinical improvement (decreases in the frequency of voice breaks, pitch breaks, and percentage aperiodicity). These data suggest a pathophysiological model for ADSD in which BTX treatment results in more efficient cortical processing of sensory information, making this information available to motor areas that use it to more effectively regulate laryngeal movements.

PET imaging of the basal ganglia

The present chapter reviews PET imaging in basal ganglia disorders; Parkinson's disease is used as a model of these disorders because the neurochemical pathobiology of this disease is well known and great advances in the imaging area have been achieved. Other basal ganglia disorders including Tourette's syndrome, dystonia, Huntington's chorea and Wilson's disease are also dealt with. With PET and SPECT techniques, the whole integrative dopaminergic network of neurons can be studied, which plays an important role in differential diagnostics. Furthermore, pharmacological effects of medication can be visualized and the role of stereotaxic neurosurgery can be evaluated. Finally, functional imaging gives clues about the prognosis and rehabilitation aspects of the basal ganglia disorders.

Task-specific hand dystonia: can too much plasticity be bad for you?

Patients with occupational hand dystonias have task-specific involuntary co-contraction and overflow of activity to inappropriate muscles. This interferes with highly skilled movements such as handwriting (writer's cramp) or playing a musical instrument (musician's cramp). Transcranial stimulation methods that probe mechanisms of synaptic plasticity in the motor cortex show an abnormal modifiability of sensorimotor circuits in patients with writer's cramp, probably because homeostatic control of the range of modification is deficient. We argue that during skilled motor practice, this leads to an excessive tendency to form associations between sensory inputs and motor outputs (abnormal potentiation) and to a failure to weaken already existing associations (deficient depotentiation). Deficient homeostatic control might be an important mechanism that triggers maladaptive reorganization and produces symptoms of occupational hand dystonias.

Microstructural white matter changes in carriers of the DYT1 gene mutation

We tested the hypothesis that the DYT1 genotype is associated with a disorder of anatomical connectivity involving primarily the sensorimotor cortex. We used diffusion tensor magnetic resonance imaging (DTI) to assess the microstructure of white matter pathways in mutation carriers and control subjects. Fractional anisotropy (FA), a measure of axonal integrity and coherence, was reduced (p < 0.005) in the subgyral white matter of the sensorimotor cortex of DYT1 carriers. Abnormal anatomical connectivity of the supplementary motor area may contribute to the susceptibility of DYT1 carriers to develop clinical manifestations of dystonia.

Regional metabolism in primary torsion dystonia: effects of penetrance and genotype

BACKGROUND

The authors have previously used [18F]fluorodeoxyglucose (FDG) PET to identify a reproducible pattern of regional glucose metabolism that was expressed in both manifesting and nonmanifesting carriers of the DYT1 primary dystonia mutation.

OBJECTIVE

To identify specific regions that discriminated subjects according to clinical penetrance and genotype.

METHODS

FDG PET was used to scan 12 nonmanifesting and 11 manifesting DYT1 gene carriers, 6 nonmanifesting DYT6 gene carriers and 7 manifesting DYT6 gene carriers, as well as 11 control subjects. The data from all five groups were analyzed with statistical parametric mapping and analysis of variance with posthoc contrasts.

RESULTS

A dissociation of metabolic changes was found related to phenotype and genotype. Manifesting gene carriers of both genotypes exhibited bilateral hypermetabolism in the presupplementary motor area (Brodmann area [BA] 6) and parietal association cortices (BA 40/7) compared with the respective nonmanifesting counterparts. By contrast, genotype-specific increases in metabolism were found in the putamen, anterior cingulate (BA 24/32), and cerebellar hemispheres of DYT1 carriers. Genotype-specific changes in DYT6 involved hypometabolism of the putamen and hypermetabolism in the temporal cortex (BA 21).

CONCLUSIONS

Dystonia may be associated with abnormal movement preparation caused by defective sensorimotor integration. Whereas clinical manifestations are related to cortical dysfunction, metabolic abnormalities in subcortical structures may represent trait features that are specific for individual dystonia genotypes.

Impairment of individual finger movements in patients with hand dystonia

We investigated finger movements in patients with hand dystonia to compare the kinematics of repetitive individual and non-individual finger oppositions. We used an optoelectronic motion analysis system to record movements in 3-D space, and recorded three 5-second trials for each task, counting how many finger oppositions subjects carried out during each trial, and measured the duration and amplitude of flexions, extensions, and pauses. During tasks, normal subjects and patients carried out finger flexions faster than extensions, and invariably they paused longer before extension than before flexion. Patients were slower and paused longer than controls during both individual and non-individual oppositions. During individual finger movements, patients were disproportionately slow during extension and pause before extension. Patients with hand dystonia perform finger movements abnormally; they are affected predominantly during individual oppositions. This finding reflects the finer cortical control needed to promote and sustain this highly fractionated type of motor output, and points toward underactivity of the primary motor cortex in dystonia.

Impaired sequence learning in carriers of the DYT1 dystonia mutation

Previous positron emission tomography (PET) studies have shown that nonmanifesting carriers of the DYT1 dystonia mutation express an abnormal pattern of resting glucose metabolism. To determine whether motor behavior is impaired in these subjects, we compared movement and sequence learning in 12 clinically unaffected DYT1 carriers with 12 age-matched controls. Regional differences in brain function during task performance were assessed with simultaneous H(2) (15)O/PET. We found that motor performance was similar in the DYT1 and control groups, with no significant differences in movement time and spatial accuracy measured during each of the tasks. In contrast, sequence learning was reduced in gene carriers relative to controls (p < 0.01). PET imaging during motor execution showed increased activation in gene carriers (p < 0.001, uncorrected) in the left premotor cortex and right supplementary motor area, with concomitant reduction in the posterior medial cerebellum. During sequence learning, activation responses in DYT1 carriers were increased in the left ventral prefrontal cortex, and lateral cerebellum. These findings suggest that abnormalities in motor behavior and brain function exist in clinically nonmanifesting DYT1 carriers. Although localized increases in neural activity may enable normal movement execution in these subjects, this mechanism may not compensate for their defect in sequence learning.

Basal ganglia neuronal discharge in primary and secondary dystonia in patients undergoing pallidotomy

OBJECTIVE

Basal ganglia neuronal activity in patients undergoing posteroventral pallidotomy (PVP) for the treatment of primary genetic, secondary, or idiopathic dystonia (DYS) was studied to gain a better understanding of the pathophysiology of DYS.

METHODS

Intraoperative neurophysiological data recorded from 15 DYS patients were compared with those from 78 patients with Parkinson's disease (PD) who underwent PVP.

RESULTS

Putamen neurons in both DYS and PD patients had low discharge rates. Globus pallidus externa (GPe) and globus pallidus interna (GPi) neurons in DYS patients had significantly lower discharge rates and more irregular discharge patterns than in PD patients. GPe and GPi neurons displayed similar discharge rates and patterns in DYS, whereas in PD, the discharge rate of GPe neurons was lower than that of the GPi neurons. The discharge rate and pattern of GPe and GPi neurons in patients whose DYS was ameliorated by PVP were similar to those in DYS patients who did not benefit from PVP. No significant differences in the rate or pattern of neuronal discharge in patients with DYS of different causes were discernible. PVP was most beneficial in patients with primary genetic DYS. Anesthesia with desflurane depressed the discharge rate of the GPe and GPi neurons, particularly in patients with PD.

CONCLUSION

Significant differences in the rates and patterns of discharge of GPe and GPi neurons exist in DYS and PD. The findings are discussed with reference to the current model of the functional connections of the basal ganglia.

Abnormal cortical sensory activation in dystonia: an fMRI study

Despite the obvious motor manifestations of focal dystonia, it is recognised that the sensory system plays an important role in this condition. This functional magnetic resonance imaging study examines the sensory representations of individual digits both within the subregions of the primary sensory cortex (SI) and in other nonprimary sensory areas. Patients with focal dystonia and controls were scanned during vibrotactile stimulation of both the index (digit 2) and little (digit 5) fingers of their dominant hand (which was the affected hand in all the dystonic subjects). The activation maps obtained were analysed for location, size, and magnitude of activation and three-dimensional (3-D) orientation of digit representations. Data from both groups were compared. There were significant differences in the average 3-D separation between the two digit representations in area 1 of SI between subject groups (9.6 +/- 1.2 mm for controls and 4.1 +/- 0.2 mm for dystonic subjects). There were also strong trends for reversed ordering of the representation of the two digits in both the secondary sensory cortex and posterior parietal area between the two groups. In addition, in dystonic subjects, there was significant under activation in the secondary somatosensory cortex (SII/area 40) for both digits and in the posterior parietal area for digit 5. These results indicate the presence of widespread activation abnormalities in the cortical sensory system in dystonia.

Role of the somatosensory system in primary dystonia

The pathophysiology of dystonia is still not fully understood, but it is widely held that a dysfunction of the corticostriatal-thalamocortical motor circuits plays a major role in the pathophysiology of this syndrome. Although the most dramatic symptoms in dystonia seem to be motor in nature, marked somatosensory perceptual deficits are also present in this disease. In addition, several lines of evidence, including neurophysiological, neuroimaging and experimental findings, suggest that both motor and somatosensory functions may be defective in dystonia. Consequently, abnormal processing of the somatosensory input in the central nervous system may lead to inefficient sensorimotor integration, thus contributing substantially to the generation of dystonic movements. Whether somatosensory abnormalities are capable of triggering dystonia is an issue warranting further study. Although it seems unlikely that abnormal somatosensory input is the only drive to dystonia, it might be more correlated to the development of focal hand than generalized dystonia because local somesthetic factors are more selectively involved in the former than in the latter where, instead it seems to be a widespread deficit in processing sensory stimuli of different modality. Because basal ganglia and motor areas are heavily connected not only with somatosensory areas, but also with visual and acoustic areas, it is possible that abnormalities of other sensory modalities, such as visual and acoustic, may also be implicated in the pathophysiology of more severe forms of primary dystonia. Further studies have to be addressed to the assessment of the role of sensory modalities and their interaction on the pathophysiology of different forms of primary dystonia.

The selective gating of the N30 cortical component of the somatosensory evoked potentials of median nerve is different in the mesial and dorsolateral frontal cortex: evidence from intracerebral recordings

OBJECTIVE

The somatosensory evoked potentials of the median nerve (SEP) were registered intracerebrally in 12 subjects to elucidate the origin of N30 component and its behavior in the motor 'gating' tasks.

METHODS

The recordings were done from the electrodes which were inserted within the cortex of frontal lobe in the pre-surgical phase of epilepsy surgery. The registrations focused on the precentral N30 SEP component and its behaviour under the 'gating' paradigms. Two different 'gating' paradigms, motor and mental, were used and the SEP then were recorded in 3 conditions: (1) normal (N) paradigm, during which the subjects were instructed not to perform any movement by the stimulated hand, or to mentally simulate the movement; (2) active movement (AM) paradigm, during which the subjects were instructed to perform the active movement as the internal motor sequence test by the fingers of the hand of the stimulated limb; (3) mental movement simulation (MMS), during which the subjects were instructed to only mentally simulate the movements performed in the previous paradigm, and this 'virtual' movement also involved the hand of the stimulated limb. The recordings were done at least twice in each paradigm and averaged runs of 2000 artefact-free sweeps were used for the analysis.

RESULTS

The results demonstrated that the precentral N30 component of SEP is generated only in the pre-motor area, either dorsolaterally or mesially, which consists of Brodmann's areas 6 and 8, and their borders. Only the N30 potentials recorded there in 7 subjects had a shape and character of 'near-field' potential. The behaviour of the N30 component when recorded in the AM and MMS paradigms was different depending on the fact of whether they were recorded dorsolaterally or mesially. When there was a clear 'near-field' N30 potential recorded mesially, there was a certain gating present during the AM paradigm, i.e. during the performance of movement. However, the gating caused by the mental movement simulation in the MMS paradigm was substantially more expressed, and the N30 wave practically disappeared in some cases. On the contrary, the gating of the N30 wave, recorded in the frontal dorsolateral premotor cortex (DLPC), was almost complete when the AM (active movement) paradigm was employed, and it was only partial when the MMS paradigm (mental movement simulation) was employed.

CONCLUSIONS

The results of N30 registrations in our group of patients strongly support the theory of separate generator (or generators) of the N30 wave within the premotor cortex. They also brought forward evidence that the dorsolateral premotor cortex (Brodmann's areas 6 and 8) serves as the substrate of the 'motor execution' process, and the mesial frontal cortex (Brodmann's area 6) serves as the substrate of the 'motor planning' process. Further research should focus on the mutual registration of neurophysiological phenomena and imaging phenomena to obtain new data, which will be able to more precisely elucidate the workings of the premotor cortex during the whole process of motor performance.

Level of action of cathodal DC polarisation induced inhibition of the human motor cortex

OBJECTIVE

To induce prolonged motor cortical excitability reductions by transcranial direct current stimulation in the human.

METHODS

Cathodal direct current stimulation was applied transcranially to the hand area of the human primary motor cortex from 5 to 9 min in separate sessions in twelve healthy subjects. Cortico-spinal excitability was tested by single pulse transcranial magnetic stimulation. Transcranial electrical stimulation and H-reflexes were used to learn about the origin of the excitability changes. Neurone specific enolase was measured before and after the stimulation to prove the safety of the stimulation protocol.

RESULTS

Five and 7 min direct current stimulation resulted in motor cortical excitability reductions, which lasted for minutes after the end of stimulation, 9 min stimulation induced after-effects for up to an hour after the end of stimulation, as revealed by transcranial magnetic stimulation. Muscle evoked potentials elicited by transcranial electric stimulation and H-reflexes did not change. Neurone specific enolase concentrations remained stable throughout the experiments.

CONCLUSIONS

Cathodal transcranial direct current stimulation is capable of inducing prolonged excitability reductions in the human motor cortex non-invasively. These changes are most probably localised intracortically.

Dystonia: lessons from brain mapping

Functional neuroimaging with positron emission tomography, single photon emission computer tomography, magnetic resonance imaging, and magnetoencephalography have provided powerful tools to elucidate anatomo-functional impairment underlying movement disorders such as dystonic movements. They have revealed that presymptomatic cerebral abnormalities may be a common feature in dystonia whatever the clinical status. Techniques using specific markers have recently focused on the type of receptors that may be dysactivated and on the kind of neurotransmitter that may be dysregulated in dystonia.