The functional connectivity profile of tics and obsessive-compulsive symptoms in Tourette Syndrome

Aberrant Functional Connectivity of the Salience Network in Adult Patients with Tic Disorders: A Resting-State fMRI Study

Tic disorders (TD) are characterized by the presence of motor and/or vocal tics. Common neurophysiological frameworks suggest dysregulations of the cortico-striatal-thalamo-cortical (CSTC) brain circuit that controls movement execution. Besides common tics, there are other "non-tic" symptoms that are primarily related to sensory perception, sensorimotor integration, attention, and social cognition. The existence of these symptoms, the sensory tic triggers, and the modifying effect of attention and cognitive control mechanisms on tics may indicate the salience network's (SN) involvement in the neurophysiology of TD. Resting-state functional MRI measurements were performed in 26 participants with TD and 25 healthy controls (HC). The group differences in resting-state functional connectivity patterns were measured based on seed-to-voxel connectivity analyses. Compared to HC, patients with TD exhibited altered connectivity between the core regions of the SN (insula, anterior cingulate cortex, and temporoparietal junction) and sensory, associative, and motor-related cortices. Furthermore, connectivity changes were observed in relation to the severity of tics in the TD group. The SN, particularly the insula, is likely to be an important site of dysregulation in TD. Our results provide evidence for large-scale neural deviations in TD beyond the CSTC pathologies. These findings may be relevant for developing treatment targets.

Comparing the 'When' and the 'Where' of Electrocortical Activity in Patients with Tourette Syndrome, Body-Focused Repetitive Behaviors, and Obsessive Compulsive Disorder

Background/Objectives: Tourette Syndrome (TS), Obsessive Compulsive Disorder (OCD), and Body-Focused Repetitive Behaviors (BFRB) are three disorders that share many similarities in terms of phenomenology, neuroanatomy, and functionality. However, despite the literature pointing toward a plausible spectrum of these disorders, only a few studies have compared them. Studying the neurocognitive processes using Event-Related Potentials (ERPs) offers the advantage of assessing brain activity with excellent temporal resolution. The ERP components can then reflect specific processes known to be potentially affected by these disorders. Our first goal is to characterize 'when' in the processing stream group differences are the most prominent. The second goal is to identify 'where' in the brain the group discrepancies could be. Methods: Participants with TS (n = 24), OCD (n = 18), and BFRB (n = 16) were matched to a control group (n = 59) and were recorded with 58 EEG electrodes during a visual counting oddball task. Three ERP components were extracted (i.e., P200, N200, and P300), and generating sources were modelized with Standardized Low-Resolution Electromagnetic Tomography. Results: We showed no group differences for the P200 and N200 when controlling for anxiety and depressive symptoms, suggesting that the early cognitive processes reflected by these components are relatively intact in these populations. Our results also showed a decrease in the later anterior P300 oddball effect for the TS and OCD groups, whereas an intact oddball effect was observed for the BFRB group. Source localization analyses with sLORETA revealed activations in the lingual and middle occipital gyrus for the OCD group, distinguishing it from the other two clinical groups and the controls. Conclusions: It seems that both TS and OCD groups share deficits in anterior P300 activation but reflect distinct brain-generating source activations.

Alterations in the topological organization of the default-mode network in Tourette syndrome

BACKGROUND

The exact pathophysiology of TS is still elusive. Previous studies have identified default mode networks (DMN) abnormalities in patients with TS. However, these literatures investigated the neural activity during the tic suppression, not a true resting-state. Therefore, this study aimed to reveal the neural mechanism of Tourette's syndrome (TS) from the perspective of topological organization and functional connectivity within the DMN by electroencephalography (EEG) in resting-state.

METHODS

The study was conducted by analyzing the EEG data of TS patients with graph theory approaches. Thirty children with TS and thirty healthy controls (HCs) were recruited, and all subjects underwent resting-state EEG data acquisition. Functional connectivity within the DMN was calculated, and network properties were measured.

RESULTS

A significantly lower connectivity in the neural activity of the TS patients in the β band was found between the bilateral posterior cingulate cortex/retrosplenial cortex (t = -3.02, p < 0.05). Compared to HCs, the TS patients' local topological properties (degree centrality) in the left temporal lobe in the γ band were changed, while the global topological properties (global efficiency and local efficiency) in DMN exhibited no significant differences. It was also demonstrated that the degree centrality of the left temporal lobe in the γ band was positively related to the Yale Global Tic Severity Scale scores (r = 0.369, p = 0.045).

CONCLUSIONS

The functional connectivity and topological properties of the DMN of TS patients were disrupted, and abnormal DMN topological property alterations might affect the severity of tic in TS patients. The abnormal topological properties of the DMN in TS patients may be due to abnormal functional connectivity alterations. The findings provide novel insight into the neural mechanism of TS patients.

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.

The Dysfunctional Mechanisms Throwing Tics: Structural and Functional Changes in Tourette Syndrome

Tourette Syndrome (TS) is a high-incidence multifactorial neuropsychiatric disorder characterized by motor and vocal tics co-occurring with several diverse comorbidities, including obsessive-compulsive disorder and attention-deficit hyperactivity disorder. The origin of TS is multifactorial, with strong genetic, perinatal, and immunological influences. Although almost all neurotransmettitorial systems have been implicated in TS pathophysiology, a comprehensive neurophysiological model explaining the dynamics of expression and inhibition of tics is still lacking. The genesis and maintenance of motor and non-motor aspects of TS are thought to arise from functional and/or structural modifications of the basal ganglia and related circuitry. This complex wiring involves several cortical and subcortical structures whose concerted activity controls the selection of the most appropriate reflexive and habitual motor, cognitive and emotional actions. Importantly, striatal circuits exhibit bidirectional forms of synaptic plasticity that differ in many respects from hippocampal and neocortical plasticity, including sensitivity to metaplastic molecules such as dopamine. Here, we review the available evidence about structural and functional anomalies in neural circuits which have been found in TS patients. Finally, considering what is known in the field of striatal plasticity, we discuss the role of exuberant plasticity in TS, including the prospect of future pharmacological and neuromodulation avenues.

Altered brain connectivity in hyperkinetic movement disorders: A review of resting-state fMRI

BACKGROUND

Hyperkinetic movement disorders (HMD) manifest as abnormal and uncontrollable movements. Despite reported involvement of several neural circuits, exact connectivity profiles remain elusive.

OBJECTIVES

Providing a comprehensive literature review of resting-state brain connectivity alterations using resting-state fMRI (rs-fMRI). We additionally discuss alterations from the perspective of brain networks, as well as correlations between connectivity and clinical measures.

METHODS

A systematic review was performed according to PRISMA guidelines and searching PubMed until October 2022. Rs-fMRI studies addressing ataxia, chorea, dystonia, myoclonus, tics, tremor, and functional movement disorders (FMD) were included. The standardized mean difference was used to summarize findings per region in the Automated Anatomical Labeling atlas for each phenotype. Furthermore, the activation likelihood estimation meta-analytic method was used to analyze convergence of significant between-group differences per phenotype. Finally, we conducted hierarchical cluster analysis to provide additional insights into commonalities and differences across HMD phenotypes.

RESULTS

Most articles concerned tremor (51), followed by dystonia (46), tics (19), chorea (12), myoclonus (11), FMD (11), and ataxia (8). Altered resting-state connectivity was found in several brain regions: in ataxia mainly cerebellar areas; for chorea, the caudate nucleus; for dystonia, sensorimotor and basal ganglia regions; for myoclonus, the thalamus and cingulate cortex; in tics, the basal ganglia, cerebellum, insula, and frontal cortex; for tremor, the cerebello-thalamo-cortical circuit; finally, in FMD, frontal, parietal, and cerebellar regions. Both decreased and increased connectivity were found for all HMD. Significant spatial convergence was found for dystonia, FMD, myoclonus, and tremor. Correlations between clinical measures and resting-state connectivity were frequently described.

CONCLUSION

Key brain regions contributing to functional connectivity changes across HMD often overlap. Possible increases and decreases of functional connections of a specific region emphasize that HMD should be viewed as a network disorder. Despite the complex interplay of physiological and methodological factors, this review serves to gain insight in brain connectivity profiles across HMD phenotypes.

Die Bedeutung des Vorgefühls bei Tic-Störungen

Zusammenfassung. Theoretischer Hintergrund: Die Funktion des Vorgefühls in der Pathogenese und Aufrechterhaltung von Tic-Störungen (TS) wird in den letzten Jahren verstärkt erforscht. Die mögliche funktionelle Bedeutung der Vorgefühle wird aber noch nicht ausreichend verstanden. Methode: Im vorliegenden Review wird der Kenntnisstand zu Vorgefühlen entlang eines integrativen funktionalen Störungsmodells zusammengefasst. Ergebnisse: Im Vergleich zum Jugendalter nehmen Tic-Symptome bei Tic-Störungen im Erwachsenenalter ab, während immer mehr Betroffene ein Vorgefühl berichten. Hierbei kann zwischen einem allgemeinen Vorgefühl (trait) und dem Drang, Tics auszuführen (state) unterschieden werden. Das Vorgefühl als trait ist abhängig von der Interozeptionsfähigkeit. An den Drang, Tics auszuführen, kann habituiert werden, moderiert von Aufmerksamkeits- und Attributionsprozessen. Durch das Auflösen des Vorgefühl-Tic-Reizreaktionsmusters reduzieren sich die Tic-Symptome. Schlussfolgerung: Für weitere Erkenntnisse in Bezug auf die Bedeutung von Vorgefühl und den Drang, Tics auszuführen, sollten zukünftige Forschungsansätze Drang und allgemeine Vorgefühle in therapeutischen Interventionsstudien berücksichtigen, weitere Interozeptionsparadigmen einbeziehen und die Entwicklung von allgemeinem Vorgefühl und Drang über die Lebensspanne hinweg untersuchen.

Cognitive control inhibition networks in adulthood are impaired by early iron deficiency in infancy

Iron deficiency, a common form of micronutrient deficiency, primarily affects children and women. The principal cause of iron deficiency is undernutrition in low-income countries and malnutrition in middle to upper income regions. Iron is a key element for myelin production, neuronal metabolism, and dopamine functions. Iron deficiency in early life can alter brain development and exert long-lasting effects. Control inhibition is an executive function that involves several brain regions, including the prefrontal cortex and caudate and sub-thalamic nuclei. Dopamine is the prevalent neurotransmitter underlying cognitive inhibition. We followed cohort study participants who had iron deficiency anemia in infancy as well non-anemic controls. At 22 years of age, the participants were subjected to functional magnetic resonance imaging (fMRI) to evaluate the correlation between functional connectivity and performance on an inhibitory cognitive task (Go/No-Go). We hypothesized that former iron deficient anemic (FIDA) participants demonstrate less strength in functional connectivity compared with controls (C). There were not significant group differences in the behavioral results in terms of accuracy and response time. A continuous covariate interaction analysis of functional connectivity and the Go/No-Go scores demonstrated significant differences between the FIDA and C groups. The FIDA participants demonstrated less strength in connectivity in brain regions related to control inhibition, including the medial temporal lobe, impairment in the integration of the default mode network (indicating decreased attention and alertness), and an increase in connectivity in posterior brain areas, all of which suggest slower circuitry maturation. The results support the hypothesis that FIDA young adults show differences in the connectivity of networks related to executive functions. These differences could increase their vulnerability to develop cognitive dysfunctions or mental disorders in adulthood.

Tourette syndrome research highlights from 2020

We present here research from 2020 relevant to Tourette syndrome (TS). The authors briefly summarize a few reports they consider most important or interesting.

Recent progress on Tourette syndrome

Tic disorders and Tourette syndrome are the most common movement disorders in children and are characterized by movements or vocalizations. Clinically, Tourette syndrome is frequently associated with comorbid psychiatric symptoms. Although dysfunction of cortical–striatal–thalamic–cortical circuits with aberrant neurotransmitter function has been considered the proximate cause of tics, the mechanism underlying this association is unclear. Recently, many studies have been conducted to elucidate the epidemiology, clinical course, comorbid symptoms, and pathophysiology of tic disorders by using laboratory studies, neuroimaging, electrophysiological testing, environmental exposure, and genetic testing. In addition, many researchers have focused on treatment for tics, including behavioral therapy, pharmacological treatment, and surgical treatment. Here, we provide an overview of recent progress on Tourette syndrome.

Basal Ganglia Pathways Associated With Therapeutic Pallidal Deep Brain Stimulation for Tourette Syndrome

BACKGROUND

Deep brain stimulation (DBS) targeting the globus pallidus internus (GPi) can improve tics and comorbid obsessive-compulsive behavior (OCB) in patients with treatment-refractory Tourette syndrome (TS). However, some patients' symptoms remain unresponsive, the stimulation applied across patients is variable, and the mechanisms underlying improvement are unclear. Identifying the fiber pathways surrounding the GPi that are associated with improvement could provide mechanistic insight and refine targeting strategies to improve outcomes.

METHODS

Retrospective data were collected for 35 patients who underwent bilateral GPi DBS for TS. Computational models of fiber tract activation were constructed using patient-specific lead locations and stimulation settings to evaluate the effects of DBS on basal ganglia pathways and the internal capsule. We first evaluated the relationship between activation of individual pathways and symptom improvement. Next, linear mixed-effects models with combinations of pathways and clinical variables were compared in order to identify the best-fit predictive models of tic and OCB improvement.

RESULTS

The best-fit model of tic improvement included baseline severity and the associative pallido-subthalamic pathway. The best-fit model of OCB improvement included baseline severity and the sensorimotor pallido-subthalamic pathway, with substantial evidence also supporting the involvement of the prefrontal, motor, and premotor internal capsule pathways. The best-fit models of tic and OCB improvement predicted outcomes across the cohort and in cross-validation.

CONCLUSIONS

Differences in fiber pathway activation likely contribute to variable outcomes of DBS for TS. Computational models of pathway activation could be used to develop novel approaches for preoperative targeting and selecting stimulation parameters to improve patient outcomes.

Stressful Life Events and the Clinical Expression of Obsessive-Compulsive Disorder (OCD): An Exploratory Study

BACKGROUND

In obsessive-compulsive disorder (OCD), symptom content and severity appear to fluctuate over the course of the life cycle in accordance with stressful life events. The objective of this paper was to compare OCD patients with and without reported stressful life events (SLEs) in terms of the sociodemographics of patients and the clinical characteristics of OCD.

METHODS

This was a cross-sectional study involving 1001 patients with OCD. Data concerning SLEs were collected via the Yale OCD Natural History Questionnaire, while for OCD symptoms, the Dimensional Yale-Brown Obsessive-Compulsive Scale was used.

RESULTS

Of the 1001 OCD patients, 605 (60.5%) reported experiencing at least one SLE in their lifetime. Self-declared nonwhite skin color (odds ratio (OR) = 1.51), the presence of a sensory phenomenon (OR = 1.47), and comorbidity with post-traumatic stress disorder (PTSD) (OR = 2.38) were some of the logistic regression variables related to the reported SLEs with relevant statistical significance and risk (i.e., OR) values.

CONCLUSIONS

Our results indicate that SLEs may make Brazilian OCD patients vulnerable to the onset or exacerbation of obsessive-compulsive symptoms. The positive association of the occurrence of SLEs and sensory phenomena in this population could corroborate that environmental influences impact the neurobiology associated with OCD, and likely with other psychiatric disorders as well.

Resting-state functional connectivity in drug-naive pediatric patients with Tourette syndrome and obsessive-compulsive disorder

Previous studies in cohorts of Tourette syndrome (TS) or obsessive-compulsive disorder (OCD) patients have not clarified whether these two disorders represent two clinical conditions or they are distinct clinical phenotypes of a common disease spectrum. The study aimed to compare functional connectivity (FC) patterns in a pediatric drug-naive cohort of 16 TS patients without any comorbidity (TS), 14 TS patients with OCD (TS + OCD), and 10 pure OCD patients as well as 11 matched controls that underwent resting state fMRI. Via independent component analysis, we examined FC in the basal ganglia (BGN), sensorimotor (SMN), cerebellum (CBN), frontoparietal (FPN), default-mode (DMN), orbitofrontal (OBFN), and salience (SAN) networks among the above cohorts and their association with clinical measures. Compared to controls, TS and TS + OCD patients showed higher FC in the BGN, SMN, CBN and DMN and lower FC in the FPN and SAN. The TS and TS + OCD groups showed comparable FC in all networks. In contrast to controls, OCD patients exhibited increased FC in the BGN, SMN, CBN, DMN, FPN, and SAN. OCD patients also showed higher FC in CBN and FPN when compared with TS and TS + OCD patients both separately and as one group. Tic severity negatively correlated with FC in CBN and FPN in the TS group, while the compulsiveness scores positively correlated with the same two networks in OCD patients. Our findings suggest common FC changes in TS and TS + OCD patients. In contrast, OCD is characterized by a distinctive pattern of FC changes prominently involving the CBN and FPN.