Tourette Syndrome as a Disorder of the Social Decision Making Network

Axial tics in Tourette syndrome and chronic tic disorders

BACKGROUND

Tics are the hallmark of Tourette syndrome (TS) and chronic tic disorders (CTD). Although typically involving the face, especially at onset, tics may involve any muscle under voluntary control, including axial muscles of the neck (causing head movements), shoulders and trunk (thorax and abdomen). We aimed to characterize these tics and provide a clinical frame for their associations and complications.

MATERIALS AND METHODS

We reviewed video recordings and clinical history of 196 patients with TS or CTD according to DSM-5.

RESULTS

Any axial tic was identified in 75% of patients. Tic distribution were head (n = 113, 57.6%), shoulder (n = 91, 46.4%), and trunk (n = 63, 32.2%). There were no differences in sex, age at onset or at evaluation between patients with and without axial tics. The most common axial tics by anatomical distribution were head turning, bilateral synchronous shoulder elevation and trunk jerks; however, tic phenomenology was quite variable. A greater severity of tics (P = 0.018) was associated with axial tics in the multivariate regression analysis. Head/neck tics associated with simple phonic tics (P = 0.002); whereas shoulder and trunk tics associated with complex motor tics (P < 0.05) in a bivariate analysis. Neck pain, breathing interference, sleep limitation and radiculopathy, secondary to axial tics were complications observed in a proportion of these cases.

CONCLUSIONS

Axial tics are commonly observed in patients with TS/CTD with variable phenomenology. They associate with greater tic severity, phonic tics and complex motor tics. They may result in neck pain, breathing interference, sleeping problems and cervical spine injuries.

Tourette syndrome research highlights from 2023

In this, the tenth annual update for the F1000Research Tics collection, we summarize research reports from 2023 on Gilles de la Tourette syndrome and other tic disorders. The authors welcome article suggestions and thoughtful feedback from readers.

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.

Sex and gender in neurodevelopmental conditions

Health-related conditions often differ qualitatively or quantitatively between individuals of different birth-assigned sexes and gender identities, and/or with different gendered experiences, requiring tailored care. Studying the moderating and mediating effects of sex-related and gender-related factors on impairment, disability, wellbeing and health is of paramount importance especially for neurodivergent individuals, who are diagnosed with neurodevelopmental conditions with uneven sex/gender distributions. Researchers have become aware of the myriad influences that sex-related and gender-related variables have on the manifestations of neurodevelopmental conditions, and contemporary work has begun to investigate the mechanisms through which these effects are mediated. Here we describe topical concepts of sex and gender science, summarize current knowledge, and discuss research and clinical challenges related to autism, attention-deficit/hyperactivity disorder and other neurodevelopmental conditions. We consider sex and gender in the context of epidemiology, behavioural phenotypes, neurobiology, genetics, endocrinology and neighbouring disciplines. The available evidence supports the view that sex and gender are important contributors to the biological and behavioural variability in neurodevelopmental conditions. Methodological caveats such as frequent conflation of sex and gender constructs, inappropriate measurement of these constructs and under-representation of specific demographic groups (for example, female and gender minority individuals and people with intellectual disabilities) limit the translational potential of research so far. Future research and clinical implementation should integrate sex and gender into next-generation diagnostics, mechanistic investigations and support practices.

Establishment and evaluation of a compound fear behavior model of Tourette's syndrome in rats

Background

Tourette syndrome (TS) is a common childhood disorder characterized by unwanted movements or vocal sounds called tics. It is often accompanied by other psychobehavioral disorders, including fearful behavior. The establishment and evaluation of rat models of TS and comorbid fear can provide an experimental basis for the treatment of TS and its comorbid fear disorder.

Methods

Sixteen rats were randomly divided into a model group (n=8) and control group (n=8). In the model group, rats were injected intraperitoneally with iminodipropionitrile (IDPN) for 1 week to establish the TS model, which was followed by acoustic and electrical stimulation for 3 weeks to establish the rat models of TS and comorbid fear. The control group received intraperitoneal injection of saline for 1 week, and no further intervention was given in the last 3 weeks. The behavioral changes of the rats were observed and analyzed by the open field test (OFT). Protein kinase A (PKA), cyclic adenosine monophosphate (cAMP), and dopamine (DA) were measured by enzyme-linked immunosorbent assay (ELISA), and tyrosine hydroxylase (TH) and microRNA-134 (miRNA-134) in the brain tissue were detected by using polymerase chain reaction (PCR).

Results

One rat in the model group died on the 24th day. Compared with the control group, the model group had significantly higher scores of locomotor activity, stereotyped behavior, and motor behavior, along with prolonged freezing time and significantly lower expression of miRNA-134. The differences in the expressions of PKA, cAMP, DA, and TH in brain tissue were not statistically significant.

Conclusions

The rat models of TS and comorbid fear have similar changes in behaviors and miRNA-134 level to those in clinical settings and therefore can be used as a reliable animal model to study the mechanism of action of TS and comorbid fear.

Fish as a model in social neuroscience: conservation and diversity in the social brain network

Mechanisms for fish social behaviours involve a social brain network (SBN) which is evolutionarily conserved among vertebrates. However, considerable diversity is observed in the actual behaviour patterns amongst nearly 30000 fish species. The huge variation found in socio-sexual behaviours and strategies is likely generated by a morphologically and genetically well-conserved small forebrain system. Hence, teleost fish provide a useful model to study the fundamental mechanisms underlying social brain functions. Herein we review the foundations underlying fish social behaviours including sensory, hormonal, molecular and neuroanatomical features. Gonadotropin-releasing hormone neurons clearly play important roles, but the participation of vasotocin and isotocin is also highlighted. Genetic investigations of developing fish brain have revealed the molecular complexity of neural development of the SBN. In addition to straightforward social behaviours such as sex and aggression, new experiments have revealed higher order and unique phenomena such as social eavesdropping and social buffering in fish. Finally, observations interpreted as 'collective cognition' in fish can likely be explained by careful observation of sensory determinants and analyses using the dynamics of quantitative scaling. Understanding of the functions of the SBN in fish provide clues for understanding the origin and evolution of higher social functions in vertebrates.

The cognitive neuropsychiatry of Tourette syndrome

Introduction: Converging evidence from both clinical and experimental studies has shown that Tourette syndrome (TS) is not a unitary condition, but a cluster of multiple phenotypes, which encompass both tics and specific behavioural and cognitive symptoms (mainly attention-deficit and hyperactivity disorder and obsessive-compulsive disorder). Methods: We conducted a narrative review of the recent literature on the cognitive neuropsychiatry of TS. Results: Although clinical research has shown that TS is not associated with cognitive deficits per se, the findings of recent studies have suggested the presence of subtle alterations in specific cognitive functions. A promising line of research on imitative behaviour could provide a common background for the alterations in executive control and social cognition observed in TS. Two different (but not mutually exclusive) neurocognitive theories have recently suggested that TS could originate from altered perception-action binding and social decision-making dysfunction, respectively. Conclusions: Since the presence of behavioural comorbidities influences individualised treatment approaches, it is likely that a more precise characterisation of TS phenotypes, including cognitive aspects, will result in improved levels of care for patients with tic disorders.