Structural changes in the somatosensory system correlate with tic severity in Gilles de la Tourette syndrome

Diffusion indices alteration in major white matter tracts of children with tic disorder using TRACULA

BACKGROUND

Tic disorder is a neuropsychiatric disorder characterized by involuntary movements or vocalizations. Previous studies utilizing diffusion-weighted imaging to explore white-matter alterations in tic disorders have reported inconsistent results regarding the affected tracts. We aimed to address this gap by employing a novel tractography technique for more detailed analysis.

METHODS

We analyzed MRI data from 23 children with tic disorders and 23 healthy controls using TRActs Constrained by UnderLying Anatomy (TRACULA), an advanced automated probabilistic tractography method. We examined fractional anisotropy (FA), radial diffusivity (RD), axial diffusivity, and mean diffusivity in 42 specific significant white matter tracts.

RESULTS

Our findings revealed notable differences in the children with tic disorders compared to the control group. Specifically, there was a significant reduction in FA in the parietal part and splenium of the corpus callosum and the left corticospinal tract. Increased RD was observed in the temporal and splenium areas of the corpus callosum, the left corticospinal tract, and the left acoustic radiation. A higher mean diffusivity was also noted in the left middle longitudinal fasciculus. A significant correlation emerged between the severity of motor symptoms, measured by the Yale Global Tic Severity Scale, and FA in the parietal part of the corpus callosum, as well as RD in the left acoustic radiation.

CONCLUSION

These results indicate a pattern of reduced interhemispheric connectivity in the corpus callosum, aligning with previous studies and novel findings in the diffusion indices changes in the left corticospinal tract, left acoustic radiation, and left middle longitudinal fasciculus. Tic disorders might involve structural abnormalities in key white matter tracts, offering new insights into their pathogenesis.

Aberrant functional connectivity associated with drug response in patients with newly diagnosed epilepsy

OBJECTIVE

To analyze the local functional activity and connectivity features of the brain associated with drug response inpatients newly diagnosed with epilepsy (NDE) who are naïve to anti-seizure medication (ASM).

METHODS

Recruited patients, underwent functional magnetic resonance imaging at baseline, and were assigned to the well-controlled (WC, n = 28) or uncontrolled (UC, n = 11) groups based on their response to ASM. Healthy participants were included in the control group (HC, n = 29). The amplitudes of low-frequency fluctuation (ALFF) and fractional ALFF (fALFF) were used to measure local functional activity, and voxel-wise degree centrality (DC) and seed-based functional connectivity (FC) were used to evaluate the connecting intensity of the brain areas.

RESULTS

Compared to the HC and WC groups, the UC group had higher ALFF values in the left posterior central gyrus (PoCG.L) and left inferior temporal gyrus (ITG.L) and higher DC in the bilateral PoCG (Gaussian random field correction, voxel-level P < 0.001, and cluster-level P < 0.05). Both PoCG and ITG.L in the UC group showed stronger FC with multiple brain regions, mainly located in the occipital and temporal lobes, compared to the HC or WC group, while the WC group showed decreased or similar FC compared to the HC group.

INTERPRETATION

Excessive enhancement of brain functional activity or connecting intensity in ASM-naïve patients with NDE may be associated with a higher risk of poor drug response.

Additive and Interactive Effects of Attention-Deficit/Hyperactivity Disorder and Tic Disorder on Brain Connectivity

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) and persistent tic disorder (PTD) are two neurodevelopmental disorders that frequently co-occur. Contributions of each disorder to cognitive and behavioral deficits have been reported. In this paper, we tested 3 models of pathophysiology for the two disorders (additive, interactive, and phenotypic) using resting-state connectivity associated with each disorder separately and together.

METHODS

Participants were 148 children (55 with ADHD only, 33 with ADHD and PTD, 27 with PTD only, and 33 healthy control subjects) at ages 8 to 12 years. Following diagnostic interviews and behavioral assessment, participants underwent a 128-channel electroencephalography recording. Resting-state, cortical source-level effective connectivity was analyzed across the 4 groups using a 2 × 2 factorial design with factors of ADHD (with/without) and PTD (with/without).

RESULTS

ADHD diagnosis was the primary driver of cognitive and behavioral deficits, while deficits associated with PTD were primarily with thought problems and internalizing problems when compared with controls. Subadditive effects were observed in co-occurring ADHD+PTD for parent-rated behavioral problems and cognitive functions. Aberrant effective connectivity was primarily associated with ADHD, more specifically with lower posterior and occipital-frontal connectivity, while children with PTD exhibited greater left postcentral to precuneus connectivity. Weaker ADHD-related connectivity was associated with more severe behavioral problems, including internalizing behaviors, thought problems, and working memory deficits.

CONCLUSIONS

Similar to general behavioral deficits, aberrant resting-state neural connectivity in pediatric ADHD and PTD combines additively in co-occurring cases. The findings of this study support ADHD as a focus of treatment in comorbid cases, given the driving role of ADHD in both behavioral and neurophysiological deficits.

The microstructural change of the brain and its clinical severity association in pediatric Tourette syndrome patients

BACKGROUND

Gilles de la Tourette syndrome (GTS) is a prevalent pediatric neurological disorder. Most studies point to abnormalities in the cortico-striato-thalamocortical (CSTC) circuits. Neuroimaging studies have shown GTS's extensive impact on the entire brain. However, due to participant variability and potential drug and comorbidity impact, the results are inconsistent. To mitigate the potential impact of participant heterogeneity, we excluded individuals with comorbidities or those currently undergoing medication treatments. Based on the hypothesis of abnormality within the CSTC circuit, we investigated microstructural changes in white matter using diffusion spectrum imaging (DSI). This study offers the first examination of microstructural changes in treatment-naïve pediatric patients with pure GTS using diffusion spectrum imaging.

METHODS

This single-center prospective study involved 30 patients and 30 age- and gender-matched healthy volunteers who underwent sagittal T1-weighted MRI and DSI. We analyzed generalized fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity.

RESULTS

No significant differences were observed in mean diffusivity and axial diffusivity values between the two groups. However, the patient group exhibited significantly higher generalized fractional anisotropy values in the right frontostriatal tract of the dorsolateral prefrontal cortex, the right frontostriatal tract of the precentral gyrus, and bilateral thalamic radiation of the dorsolateral prefrontal cortex. Additionally, the generalized fractional anisotropy value of the right frontostriatal tract of the precentral gyrus is inversely correlated with the total tic severity scores at the most severe condition.

CONCLUSION

Treatment-naïve pediatric GTS patients demonstrated increased connectivity within the CSTC circuit as per diffusion spectrum imaging, indicating possible CSTC circuit dysregulation. This finding could also suggest a compensatory change. It thus underscores the necessity of further investigation into the fundamental pathological changes in GTS. Nevertheless, the observed altered connectivity in GTS patients might serve as a potential target for therapeutic intervention.

Tourette syndrome and obsessive-compulsive disorder: A comprehensive review of structural alterations and neurological mechanisms

Currently, it is possible to study the pathogenesis of Tourette's syndrome (TS) in more detail, due to more advanced methods of neuroimaging. However, medical and surgical treatment options are limited by a lack of understanding of the nature of the disorder and its relationship to some psychiatric disorders, the most common of which is obsessive-compulsive disorder (OCD). It is believed that the origin of chronic tic disorders is based on an imbalance of excitatory and inhibitory influences in the Cortico-Striato-Thalamo-Cortical circuits (CSTC). The main CSTCs involved in the pathological process have been identified by studying structural and neurotransmitter disturbances in the interaction between the cortex and the basal ganglia. A neurotransmitter deficiency in CSTC has been demonstrated by immunohistochemical and genetic methods, but it is still not known whether it arises as a consequence of genetically determined disturbances of neuronal migration during ontogenesis or as a consequence of altered production of proteins involved in neurotransmitter production. The aim of this review is to describe current ideas about the comorbidity of TS with OCD, the involvement of CSTC in the pathogenesis of both disorders and the background of structural and neurotransmitter changes in CSTC that may serve as targets for drug and neuromodulatory treatments.

White matter alterations in drug-naïve children with Tourette syndrome and obsessive-compulsive disorder

Tourette syndrome (TS) and early-onset obsessive-compulsive disorder (OCD) are frequently associated and conceptualized as distinct phenotypes of a common disease spectrum. However, the nature of their relationship is still largely unknown on a pathophysiological level. In this study, early structural white matter (WM) changes investigated through diffusion tensor imaging (DTI) were compared across four groups of drug-naïve children: TS-pure (n = 16), TS+OCD (n = 14), OCD (n = 10), and 11 age-matched controls. We analyzed five WM tracts of interest, i.e., cortico-spinal tract (CST), anterior thalamic radiations (ATR), inferior longitudinal fasciculus (ILF), corpus callosum (CC), and cingulum and evaluated correlations of DTI changes to symptom severity. Compared to controls, TS-pure and TS+OCD showed a comparable pattern of increased fractional anisotropy (FA) in CST, ATR, ILF and CC, with FA changes displaying negative correlation to tic severity. Conversely, in OCD, FA decreased in all WM tracts (except for the cingulum) compared to controls and negatively correlated to symptoms. We demonstrate different early WM microstructural alterations in children with TS-pure/TS+OCD as opposed to OCD. Our findings support the conceptualization of TS+OCD as a subtype of TS while suggesting that OCD is characterized by independent pathophysiological mechanisms affecting WM development.

Identify aberrant white matter microstructure in ASD, ADHD and other neurodevelopmental disorders: A meta-analysis of diffusion tensor imaging studies

BACKGROUND

Neurodevelopmental disorders (NDDs) usually present overlapping symptoms. Abnormal white matter (WM) microstructure has been found in these disorders. Identification of common and unique neural abnormalities across NDDs could provide further insight into the underlying pathophysiological mechanisms.

METHODS

We performed a voxel-based meta-analysis of whole-brain diffusion tensor imaging (DTI) studies in autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD) and other NDDs. A systematic literature search was conducted through March 2020 to identify studies that compared measures of WM microstructure between patients with NDDs and neurotypical controls. Peak voxel coordinates were meta-analyzed via anisotropic effect size-signed differential mapping (AES-SDM) as well as activation likelihood estimation (ALE).

RESULTS

Our final sample included a total of 4137 subjects from 66 studies across five NDDs. Fractional anisotropy (FA) reductions were found in the splenium of the CC in ADHD, and the genu and splenium of CC in ASD. And mean diffusivity (MD) increases were shown in posterior thalamic radiation in ASD. No consistent abnormalities were detected in specific learning disorder, motor disorder or communication disorder. Significant differences between child/adolescent and adult patients were found within the CC across NDDs, reflective of aberrant neurodevelopmental processes in NDDs.

CONCLUSIONS

The current study demonstrated atypical WM patterns in ASD, ADHD and other NDDs. Microstructural abnormalities in the splenium of the CC were possibly shared among ASD and ADHD.

Altered Interoceptive Sensibility in Adults With Chronic Tic Disorder

BACKGROUND

Interoception refers to the sensing, interpretation, integration, and regulation of signals about the body's internal physiological state. Interoceptive sensibility is the subjective evaluation of interoceptive experience, as assessed by self-report measures, and is abnormal in numerous neuropsychiatric disorders. Research examining interoceptive sensibility in individuals with chronic tic disorders (CTDs), however, has yielded conflicting results, likely due to methodologic differences between studies and small sample sizes.

OBJECTIVE

We sought to compare interoceptive sensibility between adults with CTD and healthy controls, adjusting for co-occurring psychiatric symptoms, and to examine the relationship of interoceptive sensibility with other CTD clinical features, in particular, premonitory urge.

METHODS

We recruited adults with CTDs and sex- and age-matched healthy controls to complete the Multidimensional Assessment of Interoceptive Awareness, Version 2 (MAIA-2), as well as a battery of measures assessing psychiatric symptoms prevalent in CTD populations. CTD participants additionally completed scales quantifying tic severity, premonitory urge severity, and health-related quality of life. We conducted between-group contrasts (Wilcoxon rank-sum test) for each MAIA-2 subscale, analyzed the effect of psychiatric symptoms on identified between-group differences (multivariable linear regression), and examined within-group relationships between MAIA-2 subscales and other clinical measures (Spearman rank correlations, multivariable linear regression).

RESULTS

Between adults with CTD (n = 48) and healthy controls (n = 48), MAIA-2 Noticing and Not-Worrying subscale scores significantly differed. After adjusting for covariates, lower MAIA-2 Not-Worrying subscale scores were significantly associated with female sex (β = 0.42, p < 0.05) and greater severity of obsessive-compulsive symptoms (β = -0.028, p < 0.01), but not with CTD diagnosis. After adjusting for severity of tics and obsessive-compulsive symptoms, a composite of MAIA-2 Noticing, Attention Regulation, Emotional Awareness, Self-Regulation, Body Listening, and Trusting subscales (β = 2.52, p < 0.01) was significantly associated with premonitory urge.

CONCLUSION

Study results revealed three novel findings: adults with CTD experience increased anxiety-associated somatization and increased general body awareness relative to healthy controls; anxiety-associated somatization is more closely associated with sex and obsessive-compulsive symptoms than with CTD diagnosis; and increased general body awareness is associated with greater severity of premonitory urges.

Towards an Ideology-Free, Truly Mechanistic Health Psychology

Efficient transfer of concepts and mechanistic insights from the cognitive to the health sciences and back requires a clear, objective description of the problem that this transfer ought to solve. Unfortunately, however, the actual descriptions are commonly penetrated with, and sometimes even motivated by, cultural norms and preferences, a problem that has colored scientific theorizing about behavioral control—the key concept for many psychological health interventions. We argue that ideologies have clouded our scientific thinking about mental health in two ways: by considering the societal utility of individuals and their behavior a key criterion for distinguishing between healthy and unhealthy people, and by dividing what actually seem to be continuous functions relating psychological and neurocognitive underpinnings to human behavior into binary, discrete categories that are then taken to define clinical phenomena. We suggest letting both traditions go and establish a health psychology that restrains from imposing societal values onto individuals, and then taking the fit between behavior and values to conceptualize unhealthiness. Instead, we promote a health psychology that reconstructs behavior that is considered to be problematic from well-understood mechanistic underpinnings of human behavior.

Reduced Axon Calibre in the Associative Striatum of the Sapap3 Knockout Mouse

Pathological repetitive behaviours are a common feature of various neuropsychiatric disorders, including compulsions in obsessive-compulsive disorder or tics in Gilles de la Tourette syndrome. Clinical research suggests that compulsive-like symptoms are related to associative cortico-striatal dysfunctions, and tic-like symptoms to sensorimotor cortico-striatal dysfunctions. The Sapap3 knockout mouse (Sapap3-KO), the current reference model to study such repetitive behaviours, presents both associative as well as sensorimotor cortico-striatal dysfunctions. Previous findings point to deficits in both macro-, as well as micro-circuitry, both of which can be affected by neuronal structural changes. However, to date, structural connectivity has not been analysed. Hence, in the present study, we conducted a comprehensive structural characterisation of both associative and sensorimotor striatum as well as major cortical areas connecting onto these regions. Besides a thorough immunofluorescence study on oligodendrocytes, we applied AxonDeepSeg, an open source software, to automatically segment and characterise myelin thickness and axon area. We found that axon calibre, the main contributor to changes in conduction speed, is specifically reduced in the associative striatum of the Sapap3-KO mouse; myelination per se seems unaffected in associative and sensorimotor cortico-striatal circuits.

The Cerebellum in Drug-naive Children with Tourette Syndrome and Obsessive–Compulsive Disorder

Tourette syndrome (TS) and obsessive–compulsive disorder (OCD) are two neurodevelopmental disorders characterized by repetitive behaviors. Our recent study in drug-naive children with TS and OCD provided evidence of cerebellar involvement in both disorders. In addition, cerebellar functional connectivity (FC) was similar in TS patients without comorbidities (TSpure) and TS patients with OCD comorbidity (TS + OCD), but differed in pure OCD patients. To investigate in detail the cerebellar involvement in the pathophysiology of TS and OCD, we explored cerebellar structural and functional abnormalities in drug-naive children with TSpure, TS + OCD, and OCD and assessed possible correlations with severity scores. We examined 53 drug-naive children, classified as TSpure (n = 16), TS + OCD (n = 14), OCD (n = 11), or controls (n = 12). All subjects underwent a multimodal 3T magnetic resonance imaging examination. Cerebellar lobular volumes and quantitative diffusion tensor imaging parameters of cerebellar peduncles were used as measures of structural integrity. The dentate nucleus was selected as a region of interest to examine cerebello-cerebral functional connectivity alterations. Structural analysis revealed that both TSpure and TS + OCD patients had higher fractional anisotropy in cerebellar peduncles than controls. Conversely, OCD patients were characterized by lower fractional anisotropy than both controls and TSpure and TS + OCD patients. Lastly, cerebellar functional connectivity analysis revealed significant alterations in the cerebello-thalamo-cortical circuit in TSpure, TS + OCD, and OCD patients. Early cerebellar structural and functional changes in drug-naive pediatric TSpure, TS + OCD, and OCD patients support a primary role of the cerebellum in the pathophysiology of these disorders.

Microstructural Abnormalities of White Matter Across Tourette Syndrome: A Voxel-Based Meta-Analysis of Fractional Anisotropy

Introduction: Tourette syndrome (TS) is a neuropsychiatric disorder with multiple motor and vocal tics whose neural basis remains unclear. Diffusion tensor imaging (DTI) studies have demonstrated white matter microstructural alternations in TS, but the findings are inconclusive. In this study, we aimed to elucidate the most consistent white matter deficits in patients with TS.

Method: By systematically searching online databases up to December 2020 for all DTI studies comparing fractional anisotropy (FA) between patients with TS and healthy controls (HCs), we conducted anisotropic effect size-signed differential mapping (AES-SDM) meta-analysis to investigate FA differences in TS, as well as performed meta-regression analysis to explore the effects of demographics and clinical characteristics on white matter abnormalities among TS.

Results: A total of eight datasets including 168 patients with TS and 163 HCs were identified. We found that TS patients showed robustly decreased FA in the corpus callosum (CC) and right inferior longitudinal fasciculus (ILF) compared with HCs. These two regions preserved significance in the sensitivity analysis. No regions of increased FA were reported. Meta-regression analysis revealed that age, sex, tic severity, or illness duration of patients with TS were not linearly correlated with decreased FA.

Conclusion: Patients with TS display deficits of white matter microstructure in the CC and right ILF known to be important for interhemispheric connections as well as long association fiber bundles within one hemisphere. Because the results reported in the primary literature were highly variable, future investigations with large samples would be required to support the identified white matter changes in TS.

Somatosensory perception-action binding in Tourette syndrome

It is a common phenomenon that somatosensory sensations can trigger actions to alleviate experienced tension. Such “urges” are particularly relevant in patients with Gilles de la Tourette (GTS) syndrome since they often precede tics, the cardinal feature of this common neurodevelopmental disorder. Altered sensorimotor integration processes in GTS as well as evidence for increased binding of stimulus- and response-related features (“hyper-binding”) in the visual domain suggest enhanced perception–action binding also in the somatosensory modality. In the current study, the Theory of Event Coding (TEC) was used as an overarching cognitive framework to examine somatosensory-motor binding. For this purpose, a somatosensory-motor version of a task measuring stimulus–response binding (S-R task) was tested using electro-tactile stimuli. Contrary to the main hypothesis, there were no group differences in binding effects between GTS patients and healthy controls in the somatosensory-motor paradigm. Behavioral data did not indicate differences in binding between examined groups. These data can be interpreted such that a compensatory “downregulation” of increased somatosensory stimulus saliency, e.g., due to the occurrence of somatosensory urges and hypersensitivity to external stimuli, results in reduced binding with associated motor output, which brings binding to a “normal” level. Therefore, “hyper-binding” in GTS seems to be modality-specific.

Tourette syndrome as a motor disorder revisited - Evidence from action coding

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Feature Binding/integration in the motor domain in Tourette Syndrome (TS) is examined.

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Motor binding processes and interleaved action are intact in TS.

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Binding processes are differentially modulated in the motor domain and sensori-motor processes.

Because tics are the defining clinical feature of Tourette syndrome, it is conceptualized predominantly as a motor disorder. There is some evidence though suggesting that the neural basis of Tourette syndrome is related to perception–action processing and binding between perception and action. However, binding processes have not been examined in the motor domain in these patients. If it is particularly perception–action binding but not binding processes within the motor system, this would further corroborate that Tourette syndrome it is not predominantly, or solely, a motor disorder.

Here, we studied N = 22 Tourette patients and N = 24 healthy controls using an established action coding paradigm derived from the Theory of Event Coding framework and concomitant EEG-recording addressing binding between a planned but postponed, and an interleaved immediate reaction with different levels of overlap of action elements. Behavioral performance during interleaved action coding was normal in Tourette syndrome. Response locked lateralized readiness potentials reflecting processes related to motor execution were larger in Tourette syndrome, but only in simple conditions. However, pre-motor processes including response preparation and configuration reflected by stimulus-locked lateralized readiness potentials were normal. This was supported by a Bayesian data analysis providing evidence for the null hypothesis. The finding that processes integrating different action-related elements prior to motor execution are normal in Tourette syndrome suggests that Tourette it is not solely a motor disorder. Considering other recent evidence, the data show that changes in “binding” in Tourette syndrome are specific for perception–action integration but not for action coding.

Altered frontal-mediated inhibition and white matter connectivity in pediatric chronic tic disorders

Tics are unique from most movement disorders, in that they are partially suppressible. As part of the inhibitory motor network, the pre-supplementary motor area is engaged in motor control and may be involved in tic physiology. We used dual-site transcranial magnetic stimulation to assess inhibitory connectivity between right pre-supplementary motor area and left primary motor cortex, which has previously been demonstrated in healthy adults. We also used diffusion tensor imaging to investigate white matter connectivity in children with chronic tics. Twelve children with chronic tic disorder and fourteen typically developing controls underwent MRI with diffusion tensor imaging indices analysis followed by single and paired-pulse transcranial magnetic stimulation with conditioning pulse over the right pre-supplementary motor area followed by left motor cortex test pulse. Neurophysiologic and imaging data relationships to measures of tic severity and suppressibility were also evaluated in tic patients. Pre-supplementary motor area-mediated inhibition of left motor cortex was present in healthy control children but not in chronic tic disorder participants. Less inhibition correlated with worse tic suppressibility (ρ = - 0.73, p = 0.047). Imaging analysis showed increased fractional anisotropy in the right superior longitudinal fasciculus, corpus callosum, corona radiata and posterior limb of the internal capsule (p < 0.05) in tic participants, which correlated with lower self-reported tic suppressibility (ρ = - 0.70, p = 0.05). Physiologic data revealed impaired frontal-mediated motor cortex inhibition in chronic tic participants, and imaging analysis showed abnormalities in motor pathways. Collectively, the neurophysiologic and neuroanatomic data correlate with tic suppressibility, supporting the relevancy to tic pathophysiology.

Structural connectivity predicts clinical outcomes of deep brain stimulation for Tourette syndrome

Deep brain stimulation may be an effective therapy for select cases of severe, treatment-refractory Tourette syndrome; however, patient responses are variable, and there are no reliable methods to predict clinical outcomes. The objectives of this retrospective study were to identify the stimulation-dependent structural networks associated with improvements in tics and comorbid obsessive-compulsive behaviour, compare the networks across surgical targets, and determine if connectivity could be used to predict clinical outcomes. Volumes of tissue activated for a large multisite cohort of patients (n = 66) implanted bilaterally in globus pallidus internus (n = 34) or centromedial thalamus (n = 32) were used to generate probabilistic tractography to form a normative structural connectome. The tractography maps were used to identify networks that were correlated with improvement in tics or comorbid obsessive-compulsive behaviour and to predict clinical outcomes across the cohort. The correlated networks were then used to generate 'reverse' tractography to parcellate the total volume of stimulation across all patients to identify local regions to target or avoid. The results showed that for globus pallidus internus, connectivity to limbic networks, associative networks, caudate, thalamus, and cerebellum was positively correlated with improvement in tics; the model predicted clinical improvement scores (P = 0.003) and was robust to cross-validation. Regions near the anteromedial pallidum exhibited higher connectivity to the positively correlated networks than posteroventral pallidum, and volume of tissue activated overlap with this map was significantly correlated with tic improvement (P < 0.017). For centromedial thalamus, connectivity to sensorimotor networks, parietal-temporal-occipital networks, putamen, and cerebellum was positively correlated with tic improvement; the model predicted clinical improvement scores (P = 0.012) and was robust to cross-validation. Regions in the anterior/lateral centromedial thalamus exhibited higher connectivity to the positively correlated networks, but volume of tissue activated overlap with this map did not predict improvement (P > 0.23). For obsessive-compulsive behaviour, both targets showed that connectivity to the prefrontal cortex, orbitofrontal cortex, and cingulate cortex was positively correlated with improvement; however, only the centromedial thalamus maps predicted clinical outcomes across the cohort (P = 0.034), but the model was not robust to cross-validation. Collectively, the results demonstrate that the structural connectivity of the site of stimulation are likely important for mediating symptom improvement, and the networks involved in tic improvement may differ across surgical targets. These networks provide important insight on potential mechanisms and could be used to guide lead placement and stimulation parameter selection, as well as refine targets for neuromodulation therapies for Tourette syndrome.

Non-invasive Brain Stimulation for the Treatment of Gilles de la Tourette Syndrome

Gilles de la Tourette Syndrome is a multifaceted neuropsychiatric disorder typically commencing in childhood and characterized by motor and phonic tics. Its pathophysiology is still incompletely understood. However, there is convincing evidence that structural and functional abnormalities in the basal ganglia, in cortico-striato-thalamo-cortical circuits, and some cortical areas including medial frontal regions and the prefrontal cortex as well as hyperactivity of the dopaminergic system are key findings. Conventional therapeutic approaches in addition to counseling comprise behavioral treatment, particularly habit reversal therapy, oral pharmacotherapy (antipsychotic medication, alpha-2-agonists) and botulinum toxin injections. In treatment-refractory Tourette syndrome, deep brain stimulation, particularly of the internal segment of the globus pallidus, is an option for a small minority of patients. Based on pathophysiological considerations, non-invasive brain stimulation might be a suitable alternative. Repetitive transcranial magnetic stimulation appears particularly attractive. It can lead to longer-lasting alterations of excitability and connectivity in cortical networks and inter-connected regions including the basal ganglia through the induction of neural plasticity. Stimulation of the primary motor and premotor cortex has so far not been shown to be clinically effective. Some studies, though, suggest that the supplementary motor area or the temporo-parietal junction might be more appropriate targets. In this manuscript, we will review the evidence for the usefulness of repetitive transcranial magnetic stimulation and transcranial electric stimulation as treatment options in Tourette syndrome. Based on pathophysiological considerations we will discuss the rational for other approaches of non-invasive brain stimulation including state informed repetitive transcranial magnetic stimulation.

Discrimination of Tourette Syndrome Based on the Spatial Patterns of the Resting-State EEG Network

Tourette syndrome (TS) is a neuropsychiatric disorder with childhood onset characterized by chronic motor and vocal tics; however, the current diagnosis of TS patients is subjective, as it is mainly assessed based on the parents' description alongside specific evaluations. The early and accurate diagnosis of TS based on its potential symptoms in children would be of benefit in their future therapy, but reliable diagnoses are difficult due to the lack of objective knowledge of the etiology and pathogenesis of TS. In this study, resting-state electroencephalograms were first collected from 36 patients and 21 healthy controls (HCs); the corresponding resting-state functional networks were then constructed, and the potential differences in network topology between the two groups were extracted by using the topology of the spatial pattern of the network (SPN). Compared to the HCs, the TS patients exhibited decreased frontotemporal/occipital/parietal connectivity. When classifying the two groups, compared to the network properties, the derived SPN features achieved a much higher accuracy of 92.31%. The intrinsic long-range connectivity between the frontal and the temporal/occipital/parietal lobes was damaged in the patient group, and this dysfunctional network pattern might serve as a reliable biomarker to differentiate TS patients from HCs as well as to assess the severity of tic symptoms.

The multimodality neuroimage findings in individuals with Tourette syndrome

Chronic tic disorder and Gilles de la Tourette syndrome are very common childhood-onset diseases. However, the pathophysiology underlying these disorders is not yet clear and most studies focus on the disinhibition of the cortico-striatal-thalamo-cortical circuit. Although dysfunction of this circuit is possible, routine clinical neuroimaging studies such as T1-weighted or T2-weighted MRI usually reveal normal results. Therefore, special neuroimaging techniques may be needed to investigate the possible microstructural or functional changes in the brain. Previous structural studies, such as those using diffusion tensor imaging, and volumetric MRI studies, revealed the main abnormalities to be located in the cortico-striatal-thalamo-cortical circuit and to be related to brain regions such as basal ganglion, thalamus, frontal cortex, and motor cortex. Some other potential regions, such as the amygdala, hippocampus or cerebellum, are also occasionally reported. Perfusion studies, such as those using positron emission tomography or functional MRI, also suggest hemodynamic changes over those brain regions related to the cortico-striatal-thalamo-cortical circuit. However, the results can be different in adult and pediatric groups, and neuroimaging findings are also inconsistent between different studies, which may reflect the high diversity of this disease or differences in enrolled patient groups with different comorbidities. Therefore, in this review article, we will focus on the neuroimaging findings relating to Tourette syndrome in different age groups using different imaging techniques.

Sensory hypersensitivity in Tourette syndrome: A review

Tourette syndrome (TS) is a neurodevelopmental disorder defined by tics, but most patients also experience bothersome sensory phenomena, in the form of premonitory urges and/or sensory hypersensitivity. Whereas premonitory urges are temporally paired with tics, sensory hypersensitivity is a constant, heightened awareness of external and/or internal stimuli. The intensity of sensory hypersensitivity does not strongly correlate with the severity of tics or premonitory urges, suggesting it is a dissociable clinical phenomenon. At least 80% of TS patients report subjectively enhanced perception of various sensory stimuli. These same patients demonstrate normal static detection thresholds. However, individuals with TS habituate abnormally to repetitive stimuli, indicating incapacity to appropriately filter redundant sensory input, i.e. impaired sensory gating. Physiologic support for this hypothesis is provided by abnormal pre-pulse inhibition (PPI) and event-related potential (ERP) investigations. Preclinical data implicates parvalbumin-positive (PV+) interneuron dysfunction in altered sensory gating in TS and other neurodevelopment disorders. Studies probing TS sensory hypersensitivity must methodically account for comorbid psychiatric conditions, namely obsessive compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD), and autism spectrum disorder (ASD), as these entities appear to involve pathophysiologic processes shared with TS. The presence of psychiatric comorbidities in TS is associated with even more profound sensory processing dysfunction. A deepened understanding of TS sensory hypersensitivity will afford novel insights into disease mechanisms, clinical phenotype, and therapeutic management.

Modulation of Fibers to Motor Cortex during Thalamic DBS in Tourette Patients Correlates with Tic Reduction

Probabilistic tractography in Tourette syndrome (TS) patients have shown an alteration in the connectivity of the primary motor cortex and supplementary motor area with the striatum and thalamus, suggesting an abnormal connectivity of the cortico-striatum-thalamocortical-pathways in TS. Deep brain stimulation (DBS) of the centromedian nucleus–nucleus ventrooralis internus (CM-Voi complex) in the thalamus is an effective treatment for refractory TS patients. We investigated the connectivity of activated fibers from CM-Voi to the motor cortex and its correlation between these projections and their clinical outcome. Seven patients with TS underwent CM-Voi-DBS surgery and were clinically evaluated preoperatively and six months postoperatively. We performed diffusion tensor imaging to display the activated fibers projecting from the CM-Voi to the different motor cortex regions of interest. These analyses showed that the extent of tic reduction during DBS is associated with the degree of stimulation-dependent connectivity between CM-Voi and the motor cortex, and in particular, an increased density of projections to the presupplementary motor area (preSMA). Non-responder patients displayed the largest amount of active fibers projecting into cortical areas other than motor cortex compared to responder patients. These findings support the notion that an abnormal connectivity of thalamocortical pathways underlies TS, and that modulation of these circuits through DBS could restore the function and reduce symptoms.

Loss in grey matter in a small network of brain areas underpins poor reactive inhibition in Obsessive-Compulsive Disorder patients

Reactive inhibition correlates with the severity of symptoms in paediatric patients with Obsessive-Compulsive Disorder (OCD) though not in those with Tourette syndrome (TS). Here we assessed whether structural alterations in both grey (GM) and white matter (WM) volumes correlate with a measure of reactive inhibition, i.e. the stop-signal reaction time (SSRT), and with clinical scale scores. Nine OCD and 11 TS uncomplicated drug-naïve paediatric patients and 12 age-matched controls underwent 3T magnetic resonance imaging scanning. Between-group differences in GM and WM volumes across the whole brain were assessed. Outside the scanner, patients performed a reaching version of the stop-signal task. Both behavioural inhibitory control and neuroimaging measures were normal in TS patients. By contrast, OCD patients exhibited a significant loss in GM volume in five areas. The GM volume of the left inferior frontal gyrus was inversely correlated with the length of the SSRT, the left mid-cingulate gyrus and the right middle frontal gyrus were inversely correlated with the severity of OCD symptoms, and the left insula and the right medial orbitofrontal gyrus were inversely correlated with both. These results indicate that cortical areas showing GM loss in OCD patients are also involved in the network subserving reactive inhibition.

The involvement of altered sensory modulation in neurological conditions and its relevance to neuro-rehabilitation: a narrative literature review

PURPOSE

Neurological conditions are frequently described and treated with emphasis on primarily body dysfunctions that appear in the diagnostic criteria. This perspective paper aims to provide knowledge about the involvement of secondary body dysfunctions - altered sensory modulation - in neurological conditions and their relevance to neuro-rehabilitation. This paper refers to children and adults, to provide a life span view. Health models and approaches are discussed to bring ideas for optimizing rehabilitation.

METHODS

Perspective based on narrative literature review.

RESULTS

Altered sensory modulation is prevalent in neurological conditions. It is related to clinical symptoms, comorbidities and severity level. Many studies focus on specific modalities and on laboratory/clinical measurements. However, information gathered from subjective measures reflects the alterations in various sensory modalities and their negative impacts on the individuals' daily activity performance, participation and quality of life (QOL).

CONCLUSIONS

Neuro-rehabilitation should consider altered sensory modulation in neurological conditions, apply health models with broad perspective, as the ICF, with multi-disciplinary team, objective and subjective measures to understand how pathogenic mechanisms in primary and secondary body dysfunctions impact the performance and participation in daily life. This approach may optimize the individuals' involvement in therapy, enhance daily function and QOL and elevate intervention success.Implications for rehabilitationSensory modulation should be evaluated in children and adults with neurologic conditions.The evaluation and intervention should refer to the involvement of altered sensory modulation in the conditions' clinical characteristics, severity and comorbidities.In case altered sensory modulation is found, the evaluation and intervention should incorporate a multi-disciplinary collaboration and health models such as the ICF model, to optimize neuro-rehabilitation efficiency.Objective measures should be applied to profile altered sensory modulation and its role in pathogenic mechanisms.Subjective measures should also be used to reflect the expressions of altered sensory modulation as experienced by the individual (and family members), in daily life scenarios.By bridging between the clinic and the individuals' real-life context, rehabilitation process and outcomes may be optimized, in terms of the individual's greater involvement in therapy, better function and quality of life.

Subjective embodiment during the rubber hand illusion predicts severity of premonitory sensations and tics in Tourette Syndrome

In Tourette Syndrome, the expression of tics and commonly preceding premonitory sensations is associated with perturbed subjective feelings of self-control and agency. We compared responses to the Rubber Hand Illusion in 23 adults with TS and 22 controls. Both TS and control participants reported equivalent subjective embodiment of the artificial hand: feelings of ownership, location, and agency were greater during synchronous visuo-tactile stimulation, compared to asynchronous. However, individuals with TS did not manifest greater proprioceptive drift, an objective marker of embodiment observed in controls. An 'embodiment prediction error' index of the difference between subjective embodiment and objective proprioceptive drift correlated with severity of premonitory sensations. Feelings of ownership also correlated with premonitory sensation severity, and feelings of agency with tic severity. These findings suggest that subjective bodily ownership, as measured by the rubber hand illusion, contributes to susceptibility to the premonitory sensations that may be a precipitating factor in tics.

Associative plasticity in supplementary motor area - motor cortex pathways in Tourette syndrome

The important role of the supplementary motor area (SMA) in the generation of tics and urges in Gilles de la Tourette syndrome (GTS) is underscored by an increased SMA-motor cortex (M1) connectivity. However, whether plasticity is also altered in SMA-M1 pathways is unclear. We explored whether SMA-M1 plasticity is altered in patients with Tourette syndrome. 15 patients with GTS (mean age of 33.4 years, SD = 9.9) and 19 age and sex matched healthy controls were investigated with a paired association stimulation (PAS) protocol using three transcranial magnetic stimulation (TMS) coils stimulating both M1 and the SMA. Standard clinical measures for GTS symptoms were collected. There was a significant PAS effect showing that MEP amplitudes measured in blocks during and after PAS were significantly higher compared to those in the first block. However, the degree of PAS was not differentially modulated between patients and controls as shown by a Bayesian data analysis. PAS effects in GTS correlated positively with the YGTSS motor tic severity. Plasticity previously reported to be altered in sensorimotor pathways in GTS is normal in SMA-M1 projections suggesting that the dysfunction of the SMA in GTS is not primarily related to altered plasticity in SMA-M1 connections.

The PNKD gene is associated with Tourette Disorder or Tic disorder in a multiplex family

Tourette Disorder (TD) is a childhood-onset neuropsychiatric and neurodevelopmental disorder characterized by the presence of both motor and vocal tics. The genetic architecture of TD is believed to be complex and heterogeneous. Nevertheless, DNA sequence variants co-segregating with TD phenotypes within multiplex families have been identified. This report examines whole exomes of affected and unaffected individuals in a multiplex TD family to discover genes involved in the TD etiology. We performed whole exome sequencing on six out of nine members in a three-generation TD multiplex family. Putative deleterious sequence variants co-segregating with TD patients were identified by our in-house bioinformatics pipeline. Induced pluripotent stem cells (iPSCs) were generated from one unaffected and two TD affected individuals. Neurons were derived from the iPSCs and biochemical assays were conducted to evaluate possible molecular differences between affected and unaffected. A rare heterozygous nonsense mutation in PNKD was co-segregated with TD in this multiplex family. Transcript and protein levels of the PNKD long isoform were reduced in neurons derived from the individuals with TD due to the nonsense mutation, indicating nonsense-mediated mRNA decay. We demonstrated that the PNKD long isoform monomer oligomerizes with itself as well as interacts with the synaptic active zone protein RIMS1α. We concluded that reduced PNKD long isoform levels are detected in all affected individuals and we provide evidence for a mechanism whereby this might contribute to the TD phenotype.

Centrality of prefrontal and motor preparation cortices to Tourette Syndrome revealed by meta-analysis of task-based neuroimaging studies

Tourette Syndrome (TS) is a neurodevelopmental condition characterized by chronic multiple tics, which are experienced as compulsive and 'unwilled'. Patients with TS can differ markedly in the frequency, severity, and bodily distribution of tics. Moreover, there are high comorbidity rates with attention deficit hyperactivity disorder (ADHD), obsessive compulsive disorder (OCD), anxiety disorders, and depression. This complex clinical profile may account for apparent variability of findings across neuroimaging studies that connect neural function to cognitive and motor behavior in TS. Here we crystalized information from neuroimaging regarding the functional circuitry of TS, and furthermore, tested specifically for neural determinants of tic severity, by applying activation likelihood estimation (ALE) meta-analyses to neuroimaging (activation) studies of TS. Fourteen task-based studies (13 fMRI and one H2O-PET) met rigorous inclusion criteria. These studies, encompassing 25 experiments and 651 participants, tested for differences between TS participants and healthy controls across cognitive, motor, perceptual and somatosensory domains. Relative to controls, TS participants showed distributed differences in the activation of prefrontal (inferior, middle, and superior frontal gyri), anterior cingulate, and motor preparation cortices (lateral premotor cortex and supplementary motor area; SMA). Differences also extended into sensory (somatosensory cortex and the lingual gyrus; V4); and temporo-parietal association cortices (posterior superior temporal sulcus, supramarginal gyrus, and retrosplenial cortex). Within TS participants, tic severity (reported using the Yale Global Tic Severity Scale; YGTSS) selectively correlated with engagement of SMA, precentral gyrus, and middle frontal gyrus across tasks. The dispersed involvement of multiple cortical regions with differences in functional reactivity may account for heterogeneity in the symptomatic expression of TS and its comorbidities. More specifically for tics and tic severity, the findings reinforce previously proposed contributions of premotor and lateral prefrontal cortices to tic expression.

White matter developmental trajectories associated with persistence and recovery of childhood stuttering

Stuttering affects the fundamental human ability of fluent speech production, and can have a significant negative impact on an individual's psychosocial development. While the disorder affects about 5% of all preschool children, approximately 80% of them recover naturally within a few years of stuttering onset. The pathophysiology and neuroanatomical development trajectories associated with persistence and recovery of stuttering are still largely unknown. Here, the first mixed longitudinal diffusion tensor imaging (DTI) study of childhood stuttering has been reported. A total of 195 high quality DTI scans from 35 children who stutter (CWS) and 43 controls between 3 and 12 years of age were acquired, with an average of three scans per child, each collected approximately a year apart. Fractional anisotropy (FA), a measure reflecting white matter structural coherence, was analyzed voxel-wise to examine group and age-related differences using a linear mixed-effects (LME) model. Results showed that CWS exhibited decreased FA relative to controls in the left arcuate fasciculus, underlying the inferior parietal and posterior temporal areas, and the mid body of corpus callosum. Further, white matter developmental trajectories reflecting growth rate of these tract regions differentiated children with persistent stuttering from those who recovered from stuttering. Specifically, a reduction in FA growth rate (i.e., slower FA growth with age) in persistent children relative to fluent controls in the left arcuate fasciculus and corpus callosum was found, which was not evident in recovered children. These findings provide first glimpses into the possible neural mechanisms of onset, persistence, and recovery of childhood stuttering. Hum Brain Mapp 38:3345-3359, 2017. © 2017 Wiley Periodicals, Inc.

Toward a Multifactorial Conception of the Gilles de la Tourette Syndrome and Persistent Chronic Tic Disorder

Despite recent giant leaps in understanding Gilles de la Tourette’s syndrome (now Tourette Disorder in the DSM 5), accurate multi-modal description, rigorous assessment procedures, and the improvement of evidence-based treatment currently pose a considerable challenge. In this context, the current special edition aims to elaborate three important dimensions in Tourette Disorder. Firstly, the effective characterization and etiological basis of the disorder are reviewed, since such characterization impacts accurate assessment. Secondly, subsequent articles cover the comprehensive evaluation and assessment of tic disorders, essential for treatment planning. Thirdly, the final group of articles propose novel and innovative treatment strategies for pharmacologically and behaviorally reducing tic frequency. In the current editorial address, two main issues seem crucial to the development of interventions for Tourette disorder. Primarily, integrating new technology in treatments, while supporting cognitive and behavioral recovery through learning self-controlled strategies. Additionally, the dissemination of study results to frontline resources, needs streamlining and empirically validated treatments for tic disorders should be the subject of knowledge translation to community organizations and be more widely available to the public.

Putting the Pieces Together in Gilles de la Tourette Syndrome: Exploring the Link Between Clinical Observations and the Biological Basis of Dysfunction

Gilles de la Tourette syndrome is a complex, idiopathic neuropsychiatric disorder whose pathophysiological mechanisms have yet to be elucidated. It is phenotypically heterogeneous and manifests more often than not with both motor and behavioral impairment, although tics are its clinical hallmark. Tics themselves present with a complex profile as they characteristically wax and wane and are often preceded by premonitory somatosensory sensations to which it is said a tic is the response. Highly comorbid with obsessive-compulsive disorder and attention deficit-hyperactivity disorder, it is purported to be an epigenetic, neurodevelopmental spectrum disorder with a complex genetic profile. It has a childhood onset, occurs disproportionately in males, and shows spontaneous symptomatic attenuation by adulthood in the majority of those afflicted. Although not fully understood, its neurobiological basis is linked to dysfunction in the cortico-basal ganglia-thalamo-cortical network. Treatment modalities for Tourette syndrome include behavioral, pharmacological and surgical interventions, but there is presently no cure for the disorder. For those severely affected, deep brain stimulation (DBS) has recently become a viable therapeutic option. A key factor to attaining optimal results from this surgery is target selection, a topic still under debate due to the complex clinical profile presented by GTS patients. Depending on its phenotypic expression and the most problematic aspect of the disorder for the individual, one of three brain regions is most commonly chosen for stimulation: the thalamus, globus pallidus, or nucleus accumbens. Neurophysiological analyses of intra- and post-operative human electrophysiological recordings from clinical DBS studies suggest a link between tic behavior and activity in both the thalamus and globus pallidus. In particular, chronic recordings from the thalamus have shown a correlation between symptomatology and (1) spectral activity in gamma band power and (2) theta/gamma cross frequency coherence. These results suggest gamma oscillations and theta/gamma cross correlation dynamics may serve as biomarkers for dysfunction. While acute and chronic recordings from human subjects undergoing DBS have provided better insight into tic genesis and the neuropathophysiological mechanisms underlying Tourette syndrome, these studies are still sparse and the field would greatly benefit from further investigations. This review reports data and discoveries of scientific and clinical relevance from a wide variety of methods and provides up-to-date information about our current understanding of the pathomechanisms underlying Tourette syndrome. It gives a comprehensive overview of the current state of knowledge and addresses open questions in the field.

A Review and Update on Tourette Syndrome: Where Is the Field Headed?

Tourette syndrome (TS) is a childhood onset neurologic disorder with manifestations including multiple motor and phonic tics, and in most cases a variety of behavioral comorbidities such as attention deficit hyperactivity disorder, obsessive compulsive disorder, and other impulse control disorders. Although it is considered a hereditary disorder, likely modified by environmental factors, genetic studies have yet to uncover relevant causative genes and there is no animal model that mimics the broad clinical phenomenology of TS. There has been a marked increase in the number of neurophysiological, neuroimaging, and other studies on TS. The findings from these studies, however, have been difficult to interpret because of small sample sizes, variability of symptoms across patients, and comorbidities. Although anti-dopaminergic drugs are the most widely used medications in the treatment of TS, there has been increasing interest in other drugs, behavioral therapies, and surgical approaches including deep brain stimulation. Herein, we review the current literature and discuss the complexities of TS and the challenges in understanding its pathophysiology and in selecting the most appropriate treatment. We also offer an expert's view of where the field of TS may be headed.

Neuroimaging of tic genesis: Present status and future perspectives

Tics are hyperkinetic movements that are distinctive by their variety in semiology and duration and by their ability to be modulated by cognitive control. They are the hallmark of Gilles de la Tourette syndrome. Despite the variety of clinical presentations in this syndrome, dysfunction of cortico-striato-pallido-thalamo-cortical networks is suggested as a core pathophysiological mechanism. We review recent structural and functional neuroimaging studies that focused on the anatomical substrate of tics and their possible genesis. These studies showed a consistent relationship between structural and functional abnormalities within motor cortico-basal ganglia circuits and occurrence of tics. The failure of top-down cortical control over motor pathways because of the atypical trajectory of brain development could be a possible mechanism of tic genesis. Occurrence of tics results in several adaptive mechanisms, including modification of cortico-striatal network activity (reduced functional activation of the primary motor cortex) and neurochemical (increased γ-aminobutyric acid concentrations in the supplementary motor area) and microstructural white matter pathways rearrangements.

Neural correlates of altered sensorimotor gating in boys with Tourette Syndrome: A combined EMG/fMRI study

OBJECTIVES

It has been hypothesised that altered sensorimotor gating might be a core problem in Tourette Syndrome (TS). However, the underlying neurophysiological mechanisms are elusive.

METHODS

We applied functional magnetic resonance imaging (fMRI) to investigate the neural correlates of altered sensorimotor gating by means of prepulse inhibition (PPI) in 22 boys with TS and 22 healthy boys using tactile PPI. The electromyography of the startle response was recorded simultaneously to the acquisition of the fMRI images.

RESULTS

As expected, PPI of the startle response was reduced in boys with TS compared to the healthy boys. We found decreased PPI-related blood oxygen level-dependent (BOLD) activity in boys with TS in the middle frontal gyrus, postcentral gyrus, superior parietal cortex, cingulate gyrus and caudate body. In boys with TS PPI of the startle response was positively correlated to PPI-related BOLD activity in the superior parietal cortex.

CONCLUSIONS

Our findings indicate that deficient sensorimotor gating in boys with TS is associated with reduced recruitment of brain regions responsible for the higher-order integration of somatosensory stimuli. Due to our strict sample selection we were able to reduce confounding by neural adaptation processes, long-term medication, gender or comorbidities.

Combining tract- and atlas-based analysis reveals microstructural abnormalities in early Tourette syndrome children

Tourette syndrome (TS) is a neurological disorder that causes uncontrolled repetitive motor and vocal tics in children. Examining the neural basis of TS churned out different research studies that advanced our understanding of the brain pathways involved in its development. Particularly, growing evidence points to abnormalities within the fronto-striato-thalamic pathways. In this study, we combined Tract-Based Spatial Statistics (TBSS) and Atlas-based regions of interest (ROI) analysis approach, to investigate the microstructural diffusion changes in both deep and superficial white matter (SWM) in TS children. We then characterized the altered microstructure of white matter in 27 TS children in comparison with 27 age- and gender-matched healthy controls. We found that fractional anisotropy (FA) decreases and radial diffusivity (RD) increases in deep white matter (DWM) tracts in cortico-striato-thalamo-cortical (CSTC) circuit as well as SWM. Furthermore, we found that lower FA values and higher RD values in white matter regions are correlated with more severe tics, but not tics duration. Besides, we also found both axial diffusivity and mean diffusivity increase using Atlas-based ROI analysis. Our work may suggest that microstructural diffusion changes in white matter is not only restricted to the gray matter of CSTC circuit but also affects SWM within the primary motor and somatosensory cortex, commissural and association fibers. Hum Brain Mapp 37:1903-1919, 2016. © 2016 Wiley Periodicals, Inc.

Inhibition, Disinhibition, and the Control of Action in Tourette Syndrome

Tourette syndrome (TS) is a neurological disorder characterized by vocal and motor tics. TS is associated with impairments in behavioral inhibition, dysfunctional signaling of the inhibitory neurotransmitter GABA, and alterations in the balance of excitatory and inhibitory influences within brain networks implicated in motor learning and the selection of actions. We review evidence that increased control over motor outputs, including the suppression of tics, may develop during adolescence in TS and be accompanied by compensatory, neuromodulatory, alterations in brain structure and function. In particular, we argue that increased control over motor outputs in TS is brought about by local increases in 'tonic' inhibition that lead to a reduction in the 'gain' of motor excitability.

Longitudinal Magnetic Resonance Imaging (MRI) Analysis of the Developmental Changes of Tourette Syndrome Reveal Reduced Diffusion in the Cortico-Striato-Thalamo-Cortical Pathways

There is evidence that cortico-striato-thalamo-cortical pathways are involved in Tourette syndrome. We performed a longitudinal imaging study in 22 patients and 21 healthy controls in order to examine the development of tics and its correlation with magnetic resonance imaging (MRI) findings. Patients were divided in a group with persisting and a group with remission of tics. We found a decrease in volume of left putamen in controls, but not in patients. We found changes in mean diffusivity between patients and controls in right caudate nucleus, thalamus, and frontal lobe. In contrast to controls, parallel and perpendicular diffusivity decreased in patients and were most pronounced in the patients with persisting tics compared to those with remission. The findings suggest that the development of the brain in patients with remission resembles the normal development more than in patients with persistent tics. This could reflect a change in brain structure or compensatory mechanisms in the brain.

Neurofeedback and its possible relevance for the treatment of Tourette syndrome

Neurofeedback is an increasingly recognized therapeutic option in various neuropsychiatric disorders to treat dysfunctions in cognitive control as well as disorder-specific symptoms. In this review we propose that neurofeedback may also reflect a valuable therapeutic option to treat executive control functions in Gilles-de-la-Tourette syndrome (GTS). Deficits in executive control functions when ADHD symptoms appear in GTS likely reflect pathophysiological processes in cortico-thalamic-striatal circuits and may also underlie the motor symptoms in GTS. Such executive control deficits evident in comorbid GTS/ADHD depend on neurophysiological processes well-known to be modifiable by neurofeedback. However, so far efforts to use neurofeedback to treat cognitive dysfunctions are scarce. We outline why neurofeedback should be considered a promising treatment option, what forms of neurofeedback may prove to be most effective and how neurofeedback may be implemented in existing intervention strategies to treat comorbid GTS/ADHD and associated dysfunctions in cognitive control. As cognitive control deficits in GTS mostly appear in comorbid GTS/ADHD, neurofeedback may be most useful in this frequent combination of disorders.

Altered structural connectivity of cortico-striato-pallido-thalamic networks in Gilles de la Tourette syndrome

See Jackson (doi:10.1093/brain/awu338) for a scientific commentary on this article.

The neural substrate of Gilles de la Tourette syndrome is unknown. Worbe et al. use probabilistic tractography to demonstrate widespread structural abnormalities in cortico-striato-pallido-thalamic white matter pathways—likely arising from abnormal brain development—in patients with this syndrome.

Gilles de la Tourette syndrome is a childhood-onset syndrome characterized by the presence and persistence of motor and vocal tics. A dysfunction of cortico-striato-pallido-thalamo-cortical networks in this syndrome has been supported by convergent data from neuro-pathological, electrophysiological as well as structural and functional neuroimaging studies. Here, we addressed the question of structural integration of cortico-striato-pallido-thalamo-cortical networks in Gilles de la Tourette syndrome. We specifically tested the hypothesis that deviant brain development in Gilles de la Tourette syndrome could affect structural connectivity within the input and output basal ganglia structures and thalamus. To this aim, we acquired data on 49 adult patients and 28 gender and age-matched control subjects on a 3 T magnetic resonance imaging scanner. We used and further implemented streamline probabilistic tractography algorithms that allowed us to quantify the structural integration of cortico-striato-pallido-thalamo-cortical networks. To further investigate the microstructure of white matter in patients with Gilles de la Tourette syndrome, we also evaluated fractional anisotropy and radial diffusivity in these pathways, which are both sensitive to axonal package and to myelin ensheathment. In patients with Gilles de la Tourette syndrome compared to control subjects, we found white matter abnormalities in neuronal pathways connecting the cerebral cortex, the basal ganglia and the thalamus. Specifically, striatum and thalamus had abnormally enhanced structural connectivity with primary motor and sensory cortices, as well as paracentral lobule, supplementary motor area and parietal cortices. This enhanced connectivity of motor cortex positively correlated with severity of tics measured by the Yale Global Tics Severity Scale and was not influenced by current medication status, age or gender of patients. Independently of the severity of tics, lateral and medial orbito-frontal cortex, inferior frontal, temporo-parietal junction, medial temporal and frontal pole also had enhanced structural connectivity with the striatum and thalamus in patients with Gilles de la Tourette syndrome. In addition, the cortico-striatal pathways were characterized by elevated fractional anisotropy and diminished radial diffusivity, suggesting microstructural axonal abnormalities of white matter in Gilles de la Tourette syndrome. These changes were more prominent in females with Gilles de la Tourette syndrome compared to males and were not related to the current medication status. Taken together, our data showed widespread structural abnormalities in cortico-striato-pallido-thalamic white matter pathways in patients with Gilles de la Tourette, which likely result from abnormal brain development in this syndrome.

Pediatric Tourette syndrome: insights from recent neuroimaging studies

Tourette syndrome has been examined using many different neuroimaging techniques. There has been a recent surge of neuroimaging research papers related to Tourette syndrome that are exploring many different aspects of the disorder and its comorbidities. This brief review focuses on recent MRI-based imaging studies of pediatric Tourette syndrome, including anatomical, functional, resting state, and diffusion tensor MRI techniques. Consistencies across studies are explored, and particularly important issues involved in acquiring data from this special population are discussed.

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.