Association of cortical disinhibition with tic, ADHD, and OCD severity in Tourette syndrome

Are Motor Skills and Motor Inhibitions Impaired in Tourette Syndrome? A Review

Tourette syndrome (TS) is a neurodevelopmental motor disorder described as an inability to inhibit unwanted motor movements. This article reviews research on the execution and inhibition of voluntary motor movements in TS. Over last two decades, a number of studies have addressed the structural and functional deficits associated with this syndrome. Only a limited number of studies have assessed the motor skills in these patients but have failed to reach any conclusive outcome. In the domain of response inhibition also, studies have reported arguable impairments in these patients. It is suggested that these conflicting results can be attributed to co-occurring comorbid conditions, the constraints posed by variable age groups, lack of control measures, and lack of specificity of domains addressed. This review will describe a way in which future research can be directed to increase our knowledge of this otherwise complex spectrum of disorders.

Pathophysiology of tic disorders

Tics are the defining symptom of Tourette syndrome and other tic disorders (TDs); however, they form only a part of their overall symptoms. The recent surge of studies addressing the underlying pathophysiology of tics has revealed an intricate picture involving multiple brain areas and complex pathways. The myriad of pathophysiological findings stem, at least partially, from the multifaceted properties of tics and the disorders that express them. Distinct brain pathways mediate the expression of tics, whereas others are involved in the generation of the premonitory urge, associated comorbidities, and other changes in brain state. Expression of these symptoms is controlled by additional networks underlying voluntary suppression by the patient or those reflecting overall behavioral state. This review aims to simplify the complex picture of tic pathophysiology by dividing it into these key components based on converging data from human and animal model studies. Thus, involvement of the corticobasal ganglia pathway and its interaction with motor, sensory, limbic, and executive networks in each of the components as well as their control by different neuromodulators is described. This division enables a focused definition of the neuronal systems involved in each of these processes and allows a better understanding of the pathophysiology of TDs as a whole.

Chasing tics in the human brain: development of open, scheduled and closed loop responsive approaches to deep brain stimulation for tourette syndrome

Tourette syndrome is a childhood-onset disorder characterized by a combination of motor and vocal tics, often associated with psychiatric comorbidities including attention deficit and hyperactivity disorder and obsessive-compulsive disorder. Despite an onset early in life, half of patients may present symptoms in adulthood, with variable degrees of severity. In select cases, the syndrome may lead to significant physical and social impairment, and a worrisome risk for self injury. Evolving research has provided evidence supporting the idea that the pathophysiology of Tourette syndrome is directly related to a disrupted circuit involving the cortex and subcortical structures, including the basal ganglia, nucleus accumbens, and the amygdala. There has also been a notion that a dysfunctional group of neurons in the putamen contributes to an abnormal facilitation of competing motor responses in basal ganglia structures ultimately underpinning the generation of tics. Surgical therapies for Tourette syndrome have been reserved for a small group of patients not responding to behavioral and pharmacological therapies, and these therapies have been directed at modulating the underlying pathophysiology. Lesion therapy as well as deep brain stimulation has been observed to suppress tics in at least some of these cases. In this article, we will review the clinical aspects of Tourette syndrome, as well as the evolution of surgical approaches and we will discuss the evidence and clinical responses to deep brain stimulation in various brain targets. We will also discuss ongoing research and future directions as well as approaches for open, scheduled and closed loop feedback-driven electrical stimulation for the treatment of Tourette syndrome.

Enhanced action tendencies in high versus low obsessive-compulsive symptoms: an event-related potential study

Obsessive-compulsive disorder (OCD) is an anxiety disorder characterized by repeated thoughts and behaviors. Inhibitory deficits are presumably related to the onset and maintenance of this disorder. The present study investigated whether obsessive-compulsive (OC) symptoms are related to enhanced response tendencies in reaction to external stimuli. Our goal was to search for direct evidence of an early response preparation process by examining the event-related potential (ERP) component of the readiness potential (RP). An enhanced response tendency might underlie inhibitory deficits in OCD. Response to novel stimuli was studied using a dishabituation paradigm in which a small number of schematic faces (angry or neutral) were presented. An analog sample of healthy subjects was divided into groups of high and low OC levels and high and low trait anxiety levels. The high OC group presented with a greater RP slope gradient that was enhanced under negative valence, compared to the low OC group. No such effect was found in the high versus low trait anxiety groups or in behavioral reaction times (ms). Results support the hypothesis that a stronger readiness for action might characterize subjects with OC symptoms, especially in the presence of threatening stimuli. This finding, specific to OC symptoms and not to anxiety symptoms, may underlie habitual and embodiment tendencies in OCD. This study suggests that early stages of motor preparation might be important to the etiology and maintenance of OC symptoms.

[Transcranial magnetic stimulation (TMS), inhibition processes and attention deficit/hyperactivity disorder (ADHD) - an overview]

Motor system excitability can be tested by transcranial magnetic stimulation CFMS). In this article, an overview of recent methodological developments and research findings related to attention deficit/hyperactivity disorder (ADHD) is provided. Different TMS parameters that reflect the function of interneurons in the motor cortex may represent neurophysiological markers of inhibition in ADHD, particularly the so-called intracortical inhibition. In children with a high level of hyperactivity and impulsivity, intracortical inhibition was comparably low at rest as shortly before the execution of a movement. TMS-evoked potentials can also be measured in the EEG so that investigating processes of excitability is not restricted to motor areas in future studies. The effects of methylphenidate on motor system excitability may be interpreted in the sense of a 'fine-tuning' with these mainly dopaminergic effects also depending on genetic parameters (DAT1 transporter). A differentiated view on the organization of motor control can be achieved by a combined analysis of TMS parameters and event-related potentials. Applying this bimodal approach, strong evidence for a deviant implementation of motor control in children with ADHD and probably compensatory mechanisms (with involvement of the prefrontal cortex) was obtained. These findings, which contribute to a better understanding of hyperactivity/impulsivity, inhibitory processes and motor control in ADHD as well as the mechanisms of medication, underline the relevance of TMS as a neurophysiological method in ADHD research.

Increased GABA contributes to enhanced control over motor excitability in Tourette syndrome

Tourette syndrome (TS) is a developmental neurological disorder characterized by vocal and motor tics and associated with cortical-striatal-thalamic-cortical circuit dysfunction, hyperexcitability within cortical motor areas, and altered intracortical inhibition. TS often follows a developmental time course in which tics become increasingly more controlled during adolescence in many individuals, who exhibit enhanced control over their volitional movements. Importantly, control over motor outputs appears to be brought about by a reduction in the gain of motor excitability. Here we present a neurochemical basis for a localized gain control mechanism. We used ultra-high-field (7 T) magnetic resonance spectroscopy to investigate in vivo concentrations of γ-aminobutyric acid (GABA) within primary and secondary motor areas of individuals with TS. We demonstrate that GABA concentrations within the supplementary motor area (SMA)--a region strongly associated with the genesis of motor tics in TS--are paradoxically elevated in individuals with TS and inversely related to fMRI blood oxygen level-dependent activation. By contrast, GABA concentrations in control sites do not differ from those of a matched control group. Importantly, we also show that GABA concentrations within the SMA are inversely correlated with cortical excitability in primary motor cortex and are predicted by motor tic severity and white-matter microstructure (FA) within a region of the corpus callosum that projects to the SMA within each hemisphere. Based upon these findings, we propose that extrasynaptic GABA contributes to a form of control, based upon localized tonic inhibition within the SMA, that may lead to the suppression of tics.

Tourette-like behaviors in the normal population are associated with hyperactive/impulsive ADHD-like behaviors but do not relate to deficits in conditioned inhibition or response inhibition

Attention-Deficit Hyperactivity Disorder (ADHD) and Tourette Syndrome (TS) present as distinct conditions clinically; however, comorbidity and inhibitory control deficits have been proposed for both. Whilst such deficits have been studied widely within clinical populations, findings are mixed—partly due to comorbidity and/or medication effects—and studies have rarely distinguished between subtypes of the disorders. Studies in the general population are sparse. Using a continuity approach, the present study examined (i) the relationships between inattentive and hyperactive/impulsive aspects of ADHD and TS-like behaviors in the general population, and (ii) their unique associations with automatic and executive inhibitory control, as well as (iii) yawning (a proposed behavioral model of TS). One hundred and thirty-eight participants completed self-report measures for ADHD and TS-like behaviors as well as yawning, and a conditioned inhibition task to assess automatic inhibition. A sub-sample of fifty-four participants completed three executive inhibition tasks. An exploratory factor analysis of the TS behavior checklist supported a distinction between phonic and motor like pure TS behaviors. Whilst hyperactive/impulsive aspects of ADHD were associated with increased pure and compulsive TS-like behaviors, inattention in isolation was related to reduced obsessive-compulsive TS-like behaviors. TS-like behaviors were associated with yawning during situations of inactivity, and specifically motor TS was related to yawning during stress. Phonic TS and inattention aspects of ADHD were associated with yawning during concentration/activity. Whilst executive interference control deficits were linked to hyperactive/impulsive ADHD-like behaviors, this was not the case for inattentive ADHD or TS-like behaviors, which instead related to increased performance on some measures. No associations were observed for automatic conditioned inhibition.

Reward enhances tic suppression in children within months of tic disorder onset

•

We examine a common, yet rarely studied, population: children with recent-onset tics.

•

The ability to suppress tics is present within months of tic onset.

•

Immediate, contingent reward enhances these children's ability to suppress tics.

Tic disorders are childhood onset neuropsychiatric disorders characterized by motor and/or vocal tics. Research has demonstrated that children with chronic tics (including Tourette syndrome and Chronic Tic Disorder: TS/CTD) can suppress tics, particularly when an immediate, contingent reward is given for successful tic suppression. As a diagnosis of TS/CTD requires tics to be present for at least one year, children in these tic suppression studies had been living with tics for quite some time. Thus, it is unclear whether the ability to inhibit tics is learned over time or present at tic onset. Resolving that issue would inform theories of how tics develop and how behavior therapy for tics works. We investigated tic suppression in school-age children as close to the time of tic onset as possible, and no later than six months after onset. Children were asked to suppress their tics both in the presence and absence of a contingent reward. Results demonstrated that these children, like children with TS/CTD, have some capacity to suppress tics, and that immediate reward enhances that capacity. These findings demonstrate that the modulating effect of reward on inhibitory control of tics is present within months of tic onset, before tics have become chronic.

Cortical and brainstem plasticity in Tourette syndrome and obsessive-compulsive disorder

Gilles de la Tourette syndrome is characterized by motor/vocal tics commonly associated with psychiatric disorders, including obsessive-compulsive disorder. We investigated primary motor cortex and brainstem plasticity in Tourette patients, exposed and unexposed to chronic drug treatment, with and without psychiatric disturbances. We also investigated primary motor cortex and brainstem plasticity in obsessive-compulsive disorder. We studied 20 Tourette patients with and without psychiatric disturbances, 15 with obsessive-compulsive disorder, and 20 healthy subjects. All groups included drug-naïve patients. We conditioned the left primary motor cortex with intermittent/continuous theta-burst stimulation and recorded motor evoked potentials. We conditioned the supraorbital nerve with facilitatory/inhibitory high-frequency stimulation and recorded the blink reflex late response area. In healthy subjects, intermittent theta-burst increased and continuous theta-burst stimulation decreased motor evoked potentials. Differently, intermittent theta-burst failed to increase and continuous theta-burst stimulation failed to decrease motor evoked potentials in Tourette patients, with and without psychiatric disturbances. In obsessive-compulsive disorder, intermittent/continuous theta-burst stimulation elicited normal responses. In healthy subjects and in subjects with obsessive-compulsive disorder, the blink reflex late response area increased after facilitatory high-frequency and decreased after inhibitory high-frequency stimulation. Conversely, in Tourette patients, with and without psychiatric disturbances, facilitatory/inhibitory high-frequency stimulation left the blink reflex late response area unchanged. Theta-burst and high-frequency stimulation elicited similar responses in drug-naïve and chronically treated patients. Tourette patients have reduced plasticity regardless of psychiatric disturbances. These findings suggest that abnormal plasticity contributes to the pathophysiology of Gilles de la Tourette syndrome. However, obsessive-compulsive disorder patients have normal cortical and brainstem plasticity.

Neuropsychological functioning in youth with obsessive compulsive disorder: an examination of executive function and memory impairment

Preliminary research suggests neuropsychological deficits in youth with obsessive-compulsive disorder (OCD) similar to those in adults; however, small samples and methodological confounds limit interpretation. We aimed to examine the rates and clinical correlates of cognitive sequelae in youth with OCD, focusing on executive functioning and memory abilities. Youth ages 7-17 years with OCD (N=96) completed a hypothesis-driven neuropsychological battery (including the Rey-Osterreith Complex Figure, California Verbal Learning Test, and subtests of the Delis-Kaplan Executive Function System and Wide Range Assessment of Memory and Learning) that primarily assessed executive functioning, memory and processing speed. Cognitive sequelae were identified in 65% of youth (37% using a more stringent definition of impairment). Magnitude of cognitive sequelae was not associated with OCD severity or age; however, greater neuropsychological impairments were found amongst youth prescribed atypical neuroleptics and those diagnosed with comorbid tic disorders. Comorbidity burden was associated with presence of neuropsychological impairment, but was not specific to any single test. Findings suggest that the presence of cognitive sequelae is prevalent amongst treatment-seeking youth with OCD. Deficits were found in executive functioning and non-verbal memory performance but these impairments were not associated with OCD severity.

A behavioural test battery to investigate tic-like symptoms, stereotypies, attentional capabilities, and spontaneous locomotion in different mouse strains

The preclinical study of human disorders associated with comorbidities and for which the aetiology is still unclear may substantially benefit from multi-strain studies conducted in mice. The latter can help isolating experimental populations (strains) exhibiting distinct facets in the parameters isomorphic to the symptoms of a given disorder. Through a reverse-translation approach, multi-strain studies can inform both natural predisposing factors and environmental modulators. Thus, mouse strains selected for a particular trait may be leveraged to generate hypothesis-driven studies aimed at clarifying the potential role played by the environment in modulating the exhibition of the symptoms of interest. Tourette's syndrome (TS) constitutes a paradigmatic example whereby: it is characterized by a core symptom (tics) often associated with comorbidities (attention-deficit-hyperactivity and obsessive-compulsive symptoms); it has a clear genetic origin though specific genes are, as yet, unidentified; its course (exacerbations and remissions) is under the influence of environmental factors. Based on these considerations, we tested four mouse strains (ABH, C57, CD1, and SJL) - varying along a plethora of behavioural, neurochemical, and immunological parameters - on a test battery tailored to address the following domains: tics (through the i.p. administration of the selective 5-HT2 receptor agonist DOI, 5mg/kg); locomotion (spontaneous locomotion in the home-cage); perseverative responding in an attentional set shifting task; and behavioural stereotypies in response to a single amphetamine (10mg/kg, i.p.) injection. Present data demonstrate that while ABH and SJL mice respectively exhibit selective increments in amphetamine-induced sniffing behaviour and DOI-induced tic-like behaviours, C57 and CD1 mice show a distinct phenotype, compared to other strains, in several parameters.

Motor cortical excitability assessed by transcranial magnetic stimulation in psychiatric disorders: a systematic review

BACKGROUND

Transcranial magnetic stimulation (TMS) is a popular neurostimulation technique suitable for the investigation of inhibitory and facilitatory networks in the human motor system. In the last 20 years, several studies have used TMS to investigate cortical excitability in various psychiatric disorders, leading to a consequent improvement in pathophysiological understanding. However, little is known about the overlap and specificity of these findings across these conditions.

OBJECTIVE

To provide a systematic review of TMS studies (1985-2013) focusing on motor cortical excitability in dementia, schizophrenia, affective disorders (major depression and bipolar), attention deficit hyperactivity disorder (ADHD), obsessive compulsive disorder (OCD), Tourette Syndrome (TS), substance abuse (alcohol, cocaine, cannabis, nicotine) and other disorders (borderline personality disorder, posttraumatic stress disorder (PTSD)).

METHODS

Systematic literature-based review.

RESULTS

Across disorders, patients displayed a general pattern of cortical disinhibition, while the most consistent results of reduced short-interval intracortical inhibition could be found in schizophrenia, OCD and Tourette Syndrome. In dementia, the most frequently reported finding was reduced short-latency afferent inhibition as a marker of cholinergic dysfunction.

CONCLUSIONS

The results of this systematic review indicate a general alteration in motor cortical inhibition in mental illness, rather than disease-specific changes. Changes in motor cortical excitability provide insight that can advance understanding of the pathophysiology underlying various psychiatric disorders. Further investigations are needed to improve the diagnostic application of these parameters.

Motor excitability during movement preparation in Tourette syndrome

Tourette syndrome (TS) is a neurodevelopmental disorder characterized by the occurrence of motor and vocal tics. TS has been linked to the impaired operation of cortical-striatal-thalamic-cortical circuits that give rise to hyper-excitability of cortical motor areas, which may be exacerbated by dysfunctional intra-cortical inhibitory mechanisms. That said, many individuals gain control over their tics during adolescence and it has been suggested that this increased control arises as a result of the development of mechanisms that operate to suppress corticospinal excitability (CSE) ahead of volitional movements. Here we used single-pulse transcranial magnetic stimulation (TMS) in conjunction with a manual Go/NoGo task to investigate alterations in CSE ahead of volitional movements in a group of adolescents with TS (N = 10). Our study demonstrated that CSE, as measured by TMS-induced motor-evoked potentials (MEPs), was significantly reduced in the TS group in the period immediately preceding a finger movement. More specifically, we show that individuals with TS, unlike their age-matched controls, do not exhibit the predicted increase in mean MEP amplitude and decrease in MEP variability that immediately precede the execution of volitional movements in typically developing young adults. Finally, we report that the magnitude of the rise in MEP amplitude across the movement preparation period in TS is significantly negatively correlated with clinical measures of motor tic severity, suggesting that individuals with severe motor tics are least able to modulate motor cortical excitability.

A similar but distinctive pattern of impaired cortical excitability in first-episode schizophrenia and ADHD

BACKGROUND

First-episode schizophrenia (FE-SZ) and attention deficit hyperactivity disorder (ADHD) are both neuropsychiatric disorders associated with an impaired dopaminergic transmission. Though displaying different clinical phenotypes, a common pathophysiological pathway is discussed controversially. Several studies using transcranial magnetic stimulation (TMS) revealed abnormalities in human motor cortex excitability in both schizophrenia and ADHD patients. Studies on cortical excitability comparing these two diseases directly are lacking.

METHOD

In this study, a total of 94 subjects were analyzed. Twenty-five FE-SZ patients were directly compared with 28 ADHD patients and 41 healthy controls (HC). We investigated cortical excitability (inhibitory and facilitatory networks) with single- and paired-pulse TMS to the left and right motor cortex.

RESULTS

Compared to HC, FE-SZ/ADHD patients displayed an impaired cortical inhibition over the left hemisphere. Apart from an enhanced intracortical facilitation, FE-SZ patients did not differ compared to ADHD patients in the main outcome measures. Both patient groups presented a dysfunctional hemispheric pattern of cortical inhibition and facilitation in comparison with HC.

CONCLUSION

The results of this study indicate a pattern of cortical disinhibition and abnormal hemispheric balance of intracortical excitability networks in two different psychiatric diseases. These effects might be associated with an imbalance in GABAergic and dopaminergic transmission and might provide evidence for a common pathophysiological pathway of both diseases.

Theoretical and practical considerations behind the use of laboratory animals for the study of Tourette syndrome

In the present manuscript we review a substantial body of literature describing several pre-clinical animal models designed and developed with the purpose of investigating the biological determinants of Tourette syndrome (TS). In order to map the animal models onto the theoretical background upon which they have been devised, we first define phenomenological and etiological aspects of TS and then match this information to the available pre-clinical models. Thus, we first describe the characteristic symptoms exhibited by TS patients and then a series of hypotheses attempting to identify the multifactorial causes of TS. With respect to the former, we detail the phenomenology of abnormal repetitive behaviors (tics and stereotypies), obsessive-compulsive behaviors and aberrant sensory-motor gating. With respect to the latter, we describe both potential candidate vulnerability genes and environmental factors (difficult pregnancies, psychosocial stressors and infections). We then discuss how this evidence has been translated in pre-clinical research with respect to both dependent (symptoms) and independent (etiological factors) variables. Thus, while, on the one hand, we detail the methodologies adopted to measure abnormal repetitive and obsessive-compulsive behaviors, and sensory-motor gating, on the other hand, we describe genetic engineering studies and environmental modulations aimed at reproducing the proposed biological determinants in laboratory rodents. A special emphasis is placed upon "programming" events, occurring during critical stages of early development and exerting organizational delayed consequences. In the final section, we outline a heuristic model with the purpose of integrating clinical and pre-clinical evidence in the study of TS.

NON-INVASIVE BRAIN STIMULATION IN CHILDREN: APPLICATIONS AND FUTURE DIRECTIONS

Transcranial magnetic stimulation (TMS) is a neurostimulation and neuromodulation technique that has provided over two decades of data in focal, non-invasive brain stimulation based on the principles of electromagnetic induction. Its minimal risk, excellent tolerability and increasingly sophisticated ability to interrogate neurophysiology and plasticity make it an enviable technology for use in pediatric research with future extension into therapeutic trials. While adult trials show promise in using TMS as a novel, non-invasive, non-pharmacologic diagnostic and therapeutic tool in a variety of nervous system disorders, its use in children is only just emerging. TMS represents an exciting advancement to better understand and improve outcomes from disorders of the developing brain.

The functional anatomy of Gilles de la Tourette syndrome

Gilles de la Tourette syndrome (GTS) holds a prime position as a disorder transgressing the brittle boundaries of neurology and psychiatry with an entangling web of motor and behavioral problems. With tics as the disorder's hallmark and myriads of related signs such as echo-, pali- and coprophenomena, paralleled by a broad neuropsychiatric spectrum of comorbidities encompassing attention deficit hyperactivity disorder, obsessive-compulsive disorder and self-injurious behavior and depression, GTS pathophysiology remains enigmatic. In this review, in the light of GTS phenomenology, we will focus on current theories of tic-emergence related to aberrant activity in the basal ganglia and abnormal basal ganglia-cortex interplay through cortico-striato-thalamocortical loops from an anatomical, neurophysiological and functional-neuroimaging perspective. We will attempt a holistic view to the countless major and minor drawbacks of the GTS brain and comment on future directions of neuroscientific research to elucidate this common and complex neuropsychiatric syndrome, which merits scientific understanding and social acceptance.

Time course analysis of motor excitability in a response inhibition task according to the level of hyperactivity and impulsivity in children with ADHD

Short interval intracortical inhibition (SICI) of motor cortex, measured by transcranial magnetic stimulation (TMS) in a passive (resting) condition, has been suggested as a neurophysiological marker of hyperactivity in attention-deficit/hyperactivity disorder (ADHD). The aim of this study was to determine motor excitability in a go/nogo task at stages of response preparation, activation and suppression in children with ADHD, depending on the level of hyperactivity and impulsivity. Motor evoked potentials were recorded in 29 typically developing children and 43 children with ADHD (subdivided in two groups with higher and lower levels of hyperactivity/impulsivity; H/I-high and H/I-low). In the H/I-high group, SICI was markedly reduced in the resting condition and during response preparation. Though these children were able to increase SICI when inhibiting a response, SICI was still reduced compared to typically developing children. Interestingly, SICI at rest and during response activation were comparable, which may be associated with their hypermotoric behaviour. In the H/I-low group, response activation was accompanied by a pronounced decrease of SICI, indicating reduced motor control in the context of a fast motor response. In summary, different excitability patterns were obtained for the three groups allowing a better understanding of dysfunctional response activation and inhibition processes within the motor cortex in children with ADHD.

Transcranial magnetic stimulation measures in attention-deficit/hyperactivity disorder

Children affected by attention-deficit/hyperactivity disorder demonstrate diminished intrahemispheric inhibition (short interval cortical inhibition), as measured by transcranial magnetic stimulation. This study determined whether interhemispheric inhibition (ipsilateral silent period latency) correlates with clinical behavioral rating and motor control deficits of affected children. In 114 right-handed children (aged 8-12 years; age/sex-matched; 50 affected, 64 controls), we performed comprehensive assessments of behavior, motor skills, and cognition. Transcranial magnetic stimulation reliably elicited ipsilateral silent periods in 54 children (23 affected); all were on average older than those with unobtainable measures. Mean ipsilateral silent period latency was 5 milliseconds longer in the affected group (P = 0.007). Longer latencies correlated with more severe behavioral symptom scores (r = 0.38, P = 0.007), particularly hyperactivity (r = 0.39, P = 0.006), and with worse motor ratings on the Physical and Neurological Examination for Soft Signs (r = 0.27, P = 0.05). Longer latency also correlated with short interval cortical inhibition (r = 0.36, P = 0.008). Longer ipsilateral silent period latencies suggest interhemispheric inhibitory signaling is slower in affected children. The deficit in this inhibitory measure may underlie developmental, behavioral, and motor impairments in children with attention-deficit/hyperactivity disorder.

Motor excitability is reduced prior to voluntary movements in children and adolescents with Tourette syndrome

Tourette syndrome (TS) is a neuro-developmental disorder characterized by the occurrence of motor and vocal tics: involuntary, repetitive, stereotyped behaviours that occur with a limited duration, often typically many times in a single day. Previous studies suggest that children and adolescents with TS may undergo compensatory, neuroplastic changes in brain structure and function that help them gain control over their tics. In the current study we used single-pulse and dual-site paired-pulse transcranial magnetic stimulation (TMS), in conjunction with a manual choice reaction time task that induces high levels of inter-manual conflict, to investigate this conjecture in a group of children and adolescents with TS, but without co-morbid Attention Deficit Hyperactivity Disorder (ADHD). We found that performance on the behavioural response-conflict task did not differ between the adolescents with TS and a group of age-matched typically developing individuals. By contrast, our study demonstrated that cortical excitability, as measured by TMS-induced motor-evoked potentials (MEPs), was significantly reduced in the TS group in the period immediately preceding a finger movement. This effect is interpreted as consistent with previous suggestions that the cortical hyper-excitability that may give rise to tics in TS is actively suppressed by cognitive control mechanisms. Finally, we found no reliable evidence for altered patterns of functional inter-hemispheric connectivity in TS. These results provide evidence for compensatory brain reorganization that may underlie the increased self-regulation mechanisms that have been hypothesized to bring about the control of tics during adolescence.

Deep brain stimulation of the globus pallidus internus and Gilles de la Tourette syndrome: Toward multiple networks modulation

Background:

Gilles de la Tourette's syndrome (GTS) is a complex neuropsychiatric disorder characterized by disabling motor and vocal tics. The pathophysiology of GTS remains poorly understood. Conventional treatment consists in pharmacological and behavioral treatment. For patients suffering severe adverse effects or not responding to pharmacological treatment, deep brain stimulation (DBS) presents an alternative treatment. However, the optimal target choice in DBS for GTS remains a divisive issue.

Methods:

A PubMed search from 1999 to 2012 was conducted. Thirty-three research articles reporting on DBS in patients with GTS were selected and analyzed.

Results:

Eighty-eight patients with Tourette's syndrome were treated since 1999 with DBS. The majority of patients received thalamic stimulation. Significantly fewer patients were treated with globus pallidus internus stimulation. Occasionally, the anterior limb of the internal capsule and the nucleus accumbens were implanted. The subthalamic nucleus was selected once. All targets were reported with positive results, but of variable extent. Only 14 patients exhibited level 1 evidence.

Conclusion:

In light of the wide spectrum of associated behavioral co-morbidities in GTS, multiple networks modulation may result in the most efficacious treatment strategy. The optimal locations for DBS within the cortico-basal ganglia-thalamocortical circuits remain to be established. However, at the current stage, comparison between targets should be done with great caution. Significant disparity between number of patients treated per target, methodological variability, and quality of reporting renders a meaningful comparison between targets difficult. Randomized controlled trials with larger cohorts and standardization of procedures are urgently needed.

Trajectories of attention deficit hyperactivity disorder and oppositional defiant disorder symptoms as precursors of borderline personality disorder symptoms in adolescent girls

Little empirical evidence exists regarding the developmental links between childhood psychopathology and borderline personality disorder (BPD) in adolescence. The current study addresses this gap by examining symptoms of attention deficit hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD) as potential precursors. ADHD and BPD share clinical features of impulsivity, poor self-regulation, and executive dysfunction, while ODD and BPD share features of anger and interpersonal turmoil. The study is based on annual, longitudinal data from the two oldest cohorts in the Pittsburgh Girls Study (N = 1,233). We used piecewise latent growth curve models of ADHD and ODD scores from age 8 to 10 and 10 to 13 years to examine the prospective associations between dual trajectories of ADHD and ODD symptom severity and later BPD symptoms at age 14 in girls. To examine the specificity of these associations, we also included conduct disorder and depression symptom severity at age 14 as additional outcomes. We found that higher levels of ADHD and ODD scores at age 8 uniquely predicted BPD symptoms at age 14. Additionally, the rate of growth in ADHD scores from age 10 to 13 and the rate of growth in ODD scores from 8 to 10 uniquely predicted higher BPD symptoms at age 14. This study adds to the literature on the early development of BPD by providing the first longitudinal study to examine ADHD and ODD symptom trajectories as specific childhood precursors of BPD symptoms in adolescent girls.

Motor-cortical interaction in Gilles de la Tourette syndrome

Background

In Gilles de la Tourette syndrome (GTS) increased activation of the primary motor cortex (M1) before and during movement execution followed by increased inhibition after movement termination was reported. The present study aimed at investigating, whether this activation pattern is due to altered functional interaction between motor cortical areas.

Methodology/Principal Findings

10 GTS-patients and 10 control subjects performed a self-paced finger movement task while neuromagnetic brain activity was recorded using Magnetoencephalography (MEG). Cerebro-cerebral coherence as a measure of functional interaction was calculated. During movement preparation and execution coherence between contralateral M1 and supplementary motor area (SMA) was significantly increased at beta-frequency in GTS-patients. After movement termination no significant differences between groups were evident.

Conclusions/Significance

The present data suggest that increased M1 activation in GTS-patients might be due to increased functional interaction between SMA and M1 most likely reflecting a pathophysiological marker of GTS. The data extend previous findings of motor-cortical alterations in GTS by showing that local activation changes are associated with alterations of functional networks between premotor and primary motor areas. Interestingly enough, alterations were evident during preparation and execution of voluntary movements, which implies a general theme of increased motor-cortical interaction in GTS.

Smooth pursuit and fixation ability in children with Tourette syndrome

OBJECTIVE

The smooth pursuit eye movements and fixation ability of children aged 8 to 16 years with Tourette syndrome (TS) were examined.

BACKGROUND

Although several studies have examined the saccadic ability of patients with TS, there have been only a few studies examining pursuit ability in TS.

METHOD

Pursuit gain (eye velocity/target velocity) and intrusive saccades during fixation were measured in children with TS-only, TS+attention deficit hyperactivity disorder (ADHD), and TS+ADHD+obsessive compulsive disorder (OCD), and in controls (8 to 16 y). Two pursuit tasks and 1 fixation task were used. In random pursuit 1 (RP1), each step and ramp cycle began from fixation; in random pursuit 2 (RP2), each cycle followed the next. In the fixation task, children were required to maintain fixation on a center dot and ignore distractor stimuli.

RESULTS

All children had significantly higher pursuit gains in RP2 than in RP1 when pursuing a 30 degrees/s moving target. In addition, in RP2, the TS+ADHD+OCD group displayed significantly higher pursuit gains relative to the TS-only, TS+ADHD, and control groups. In the fixation task, the TS+ADHD group exhibited significantly more intrusive saccades than the TS+ADHD+OCD and control groups.

CONCLUSIONS

Our findings support an enhanced oculomotor ability in the TS+ADHD+OCD group and the presence of an online gain control mechanism during ongoing pursuit. These findings are discussed in more detail.

Patterns of emotional-cognitive functioning in pediatric conversion patients: implications for the conceptualization of conversion disorders

OBJECTIVES

To examine patterns of emotion processing in children and adolescents with conversion disorders and to determine whether those patterns are associated with particular clusters of conversion symptoms. Autobiographical narratives were used to investigate the organization of information about distressing feelings and memories.

METHODS

Structured interviews about attachment relationships and autobiographical events were administered to 76 controls and 76 matched subjects aged 6 to 18 years. Age-appropriate assessments of attachment were used: the School-aged Assessment of Attachment for children and the Transition to Adulthood Attachment Interview for adolescents. Patterns of emotion processing were identified using dynamic-maturational model discourse analysis and categorized into four clusters: inhibitory, normative/balanced, coercive-preoccupied, and mixed inhibitory and coercive-preoccupied. These clusters were then cross-tabulated with the sensorimotor characteristics of children with conversion disorders.

RESULTS

Emotion processing in children with conversion disorders was categorized as psychological inhibition (57%), psychological coercion-preoccupation (34%), and mixed (9%). Psychological inhibition was associated with negative conversion symptoms (discrete sensorimotor deficits, p = .003) and positive conversion symptoms (tremors and tics, p = .04). Psychological coercion-preoccupation was associated with all other disturbances of motor function: bizarre gaits and postures, whole-body floppiness, and refusals to move (p < .0001). Nonepileptic seizures occurred across both groups (56% versus 42%, p = .8).

CONCLUSIONS

Contrary to the classic understanding of conversion disorder as a unified diagnostic entity with diverse symptoms, this study identified two distinct subtypes of conversion patients-those using psychological inhibition and those using psychological coercion-preoccupation-whose symptoms fell into discrete clusters. Further research is needed to determine the neural mechanisms underlying these processes.

Altered neurophysiologic response to intermittent theta burst stimulation in Tourette syndrome

BACKGROUND

The motor system in Tourette syndrome has been found to be abnormal in previous fine-motor and neurophysiologic studies.

OBJECTIVE

This novel pilot study uses repetitive transcranial magnetic stimulation as a method to characterize the neurophysiology of the motor system in Tourette syndrome.

METHOD

We investigated the modulation of cortical excitability in adult Tourette syndrome patients by measuring motor-evoked potential amplitudes before and after applying intermittent theta burst transcranial magnetic stimulation.

RESULTS

Motor-evoked potential amplitude changes over 1 and 10 minutes after intermittent theta burst transcranial magnetic stimulation were greater in 11 healthy controls than 10 adult patients with Tourette syndrome (P = 0.004).

CONCLUSIONS

This altered neurophysiologic response to intermittent theta burst stimulation may contribute to the understanding of motor cortical mechanisms in Tourette syndrome.

Reward processing abnormalities in Parkinson's disease

The primary motor cortex is important for motor learning and response selection, functions that require information on the expected and actual outcomes of behavior. Therefore, it should receive signals related to reward. Pathways from reward centers to motor cortex exist in primates. Previously, we showed that gamma aminobutyric acid-A-mediated inhibition in the motor cortex, measured by paired transcranial magnetic stimulation, changes with expectation and uncertainty of money rewards generated by a slot machine simulation. We examined the role of dopamine in this phenomenon by testing 13 mildly affected patients with Parkinson's disease, off and on dopaminergic medications, and 13 healthy, age-matched controls. Consistent with a dopaminergic mechanism, reward expectation or predictability modulated the response to paired transcranial magnetic stimulation in controls, but not in unmedicated patients. A single dose of pramipexole restored this effect of reward, mainly by increasing the paired transcranial magnetic stimulation response amplitude during low expectation. Levodopa produced no such effect. Both pramipexole and levodopa increased risk-taking behavior on the Iowa Gambling Task. However, pramipexole increased risk-taking behavior more in patients showing lower paired transcranial magnetic stimulation response amplitude during low expectation. These results provide evidence that modulation of motor cortex inhibition by reward is mediated by dopamine signaling and that the physiological state of the motor cortex changes with risk-taking tendency in patients on pramipexole. The cortical response to reward expectation may represent an endophenotype for risk-taking behavior in patients on agonist treatment.

Motor cortex inhibition: a marker of ADHD behavior and motor development in children

OBJECTIVE

Attention-deficit/hyperactivity disorder (ADHD) is a childhood-onset behavioral diagnosis in which children often fail to meet age norms in development of motor control, particularly timed repetitive and sequential movements, motor overflow, and balance. The neural substrate of this motor delay may include mechanisms of synaptic inhibition in or adjacent to the motor cortex. The primary objective of this study was to determine whether transcranial magnetic stimulation (TMS)-evoked measures, particularly short interval cortical inhibition (SICI), in motor cortex correlate with the presence and severity of ADHD in childhood as well as with commonly observed delays in motor control.

METHODS

In this case-control study, behavioral ratings, motor skills, and motor cortex physiology were evaluated in 49 children with ADHD (mean age 10.6 years, 30 boys) and 49 typically developing children (mean age 10.5 years, 30 boys), all right-handed, aged 8-12 years. Motor skills were evaluated with the Physical and Neurological Examination for Subtle Signs (PANESS) and the Motor Assessment Battery for Children version 2. SICI and other physiologic measures were obtained using TMS in the left motor cortex.

RESULTS

In children with ADHD, mean SICI was reduced by 40% (p < 0.0001) and less SICI correlated with higher ADHD severity (r = -0.52; p = 0.002). Mean PANESS motor development scores were 59% worse in children with ADHD (p < 0.0001). Worse PANESS scores correlated modestly with less SICI (r = -.30; p = 0.01).

CONCLUSION

Reduced TMS-evoked SICI correlates with ADHD diagnosis and symptom severity and also reflects motor skill development in children.

Abnormal cortical and brain stem plasticity in Gilles de la Tourette syndrome

We investigated primary motor cortex and brain stem plasticity in patients with Gilles de la Tourette syndrome. The study group comprised 12 patients with Gilles de la Tourette syndrome and 24 healthy subjects. Patients were clinically evaluated using the Yale Global Tic Severity Scale. We tested cortical plasticity by conditioning left primary motor cortex with intermittent or continuous theta-burst stimulation in 2 separate sessions. Test stimulation consisted of 20 motor-evoked potentials recorded from right first interosseous muscle before and after theta-burst stimulation. We also tested brain stem plasticity by conditioning the right supraorbital nerve with facilitatory electric high-frequency stimulation delivered at the same time as the late response of the blink reflex or inhibitory high-frequency stimulation delivered before the late response on 2 separate sessions. Test stimulation consisted of 10 blink reflexes from the right orbicularis oculi muscle before and after high-frequency stimulation. After intermittent theta-burst stimulation, motor-evoked potential amplitudes in healthy subjects increased significantly but remained unchanged in patients. Similarly, after continuous theta-burst stimulation, motor-evoked potential amplitudes decreased significantly in healthy subjects but did not in patients. After facilitatory high-frequency stimulation, the blink reflex late response area in healthy subjects increased, whereas after inhibitory high-frequency stimulation, it decreased. Conversely, in patients, both interventions left the blink reflex late response area unchanged. The lack of the expected inhibitory and facilitatory changes in motor-evoked potential amplitudes and blink reflex late response area suggests that abnormal plasticity in the primary motor cortex and brain stem play a role in the pathophysiology of Gilles de la Tourette syndrome.

Developmental malformation of the corpus callosum: a review of typical callosal development and examples of developmental disorders with callosal involvement

This review provides an overview of the involvement of the corpus callosum (CC) in a variety of developmental disorders that are currently defined exclusively by genetics, developmental insult, and/or behavior. I begin with a general review of CC development, connectivity, and function, followed by discussion of the research methods typically utilized to study the callosum. The bulk of the review concentrates on specific developmental disorders, beginning with agenesis of the corpus callosum (AgCC)-the only condition diagnosed exclusively by callosal anatomy. This is followed by a review of several genetic disorders that commonly result in social impairments and/or psychopathology similar to AgCC (neurofibromatosis-1, Turner syndrome, 22q11.2 deletion syndrome, Williams yndrome, and fragile X) and two forms of prenatal injury (premature birth, fetal alcohol syndrome) known to impact callosal development. Finally, I examine callosal involvement in several common developmental disorders defined exclusively by behavioral patterns (developmental language delay, dyslexia, attention-deficit hyperactive disorder, autism spectrum disorders, and Tourette syndrome).

Electrophysiology in Gilles de la Tourette syndrome

Abnormalities in basal ganglia–thalamocortical circuits presumably play an important role in the pathophysiology underlying the chronic motor and vocal tics that define Gilles de la Tourette syndrome (GTS). Electrophysiological techniques, above all, the use of transcranial magnetic stimulation – a noninvasive and painless tool to examine the excitability of several different circuits in the human motor cortex – has advanced our understanding of the pathophysiology. Motor thresholds are similar in GTS and healthy subjects; in the resting state, recruitment of motor-evoked potentials above threshold is more gradual in patients with GTS compared with controls. By contrast, recruitment of motor-evoked potentials during preactivation is similar in both groups, as is the duration of the cortical silent period. This suggests that the distribution of excitability in the corticospinal system in patients at rest is different to that in healthy individuals. Importantly, correlation analysis has demonstrated that reduced levels of excitability at rest relate, in pure GTS patients, to video ratings of complex tics as well as hand and finger tics, with less excitability predicting fewer tics. The correlations disappear for measures made during voluntary activation. This suggests that this is an adaptive response to abnormal basal ganglia motor cortex inputs in an effort to reduce unwanted movements, a notion supported by electroencephalogram-coherence studies that demonstrated increased cortico–cortical coupling. Compared with the healthy control group, short intracortical inhibition thresholds are similar in patients with GTS. However, above threshold short intracortical inhibition recruitment and sensory afferent inhibition, a paradigm to examine sensory motor integration, is reduced in patients with GTS. This is consistent with the suggestion that reduced excitability of cortical inhibition is one factor that contributes to the difficulty that patients have in suppressing involuntary tics. In addition, the reduced sensory afferent inhibition indicates that impaired intracortical inhibition may not be limited to the motor cortex, but also involves circuits linking sensory input and motor output.

Clinical phenomenology and phenotype variability in Tourette syndrome

Tourette syndrome (TS) is a neurodevelopmental disorder with a rich phenomenology that includes simple and complex motor and vocal tics as well as multiple comorbidities. From a nosological perspective, it is evident that a continuum of tic severity exists, of which TS is the most severe and rare form, while transient tics and chronic tics represent milder forms. From a psychopathology perspective, TS is often concurrent with obsessive-compulsive disorder (OCD) and attention deficit hyperactivity disorder (ADHD); these disorders appear to define TS "types" TS only, TS+OCD, and TS+OCD+ADHD. Additional clinical aspects of TS include more frequent than expected occurrence of anger episodes, anxiety disorders, mood disorders, impulse control disorders, learning disorders, and pervasive developmental disorders. Data reduction techniques have been used more recently to define a "simple" and "complex" tic symptom clusters or factors. Phenomenologic approaches can be used in TS to guide future pathophysiologic research.

Anxiety in boys with attention-deficit/hyperactivity disorder with and without chronic multiple tic disorder

OBJECTIVE

This study examined the psychosocial and behavioral concomitants of anxiety in clinic-referred boys with attention-deficit/hyperactivity disorder (ADHD) with and without chronic multiple tic disorder (CMTD).

METHOD

ADHD boys with (n = 65) and without (n = 94) CMTD were evaluated with measures of psychiatric symptoms, mental health risk factors, and academic and social performance.

RESULTS

Boys with CMTD evidenced more severe anxiety and less social competence and were more likely to be living with only one biological parent than the ADHD Only group, but the magnitude of group differences was generally small. The severity of generalized anxiety, separation anxiety, social phobia, and obsessive-compulsive symptoms were uniquely associated with a different pattern of risk factors, and there was some evidence that these patterns differed for the two groups of boys.

CONCLUSION

Boys with CMTD had a relatively more severe and complex pattern of anxiety that was associated with different clinical features, all of which suggests that ADHD plus CMTD might better be conceptualized as a distinct clinical entity from ADHD Only. However, findings from the extant literature are mixed, and therefore this remains a topic for further study.

Transcranial magnetic stimulation in Gilles de la Tourette syndrome

The cause of Gilles de la Tourette syndrome (GTS), a chronic motor and vocal tic disorder of childhood onset, remains unknown. Abnormalities in basal ganglia-thalamo-cortical circuits presumably play an important role in the pathophysiology underlying the involuntary tics. The use of transcranial magnetic stimulation (TMS), a noninvasive and painless tool to examine the excitability of several different circuits in the human motor cortex has advanced our understanding of the pathophysiology. Motor thresholds are similar in GTS and healthy subjects; in the resting state, recruitment of motor evoked potentials (MEPs) above threshold is more gradual in patients than controls. In contrast, recruitment of MEPs during preactivation is similar in both groups, as is the duration of the cortical silent period. This suggests that the distribution of excitability in the corticospinal system in patients at rest is different to that in healthy individuals. Importantly, correlation analysis showed that reduced levels of excitability at rest relate, in pure GTS patients, to video ratings of complex tics, and hand and finger tics, with less excitability predicting fewer tics. The correlations disappear for measures made during voluntary activation. This suggests that this is an adaptive response to abnormal basal ganglia-motor cortex inputs in an effort to reduce unwanted movements, a notion supported by electroencephalography-coherence studies that show increased cortico-cortical coupling. Compared to the healthy control group, short intracortical inhibition (SICI) thresholds are similar. However, above-threshold SICI recruitment and sensory afferent inhibition (SAI), a paradigm to examine sensory motor integration, are reduced in patients. This is consistent with the suggestion that reduced excitability of cortical inhibition is one factor that contributes to the difficulty that patients have in suppressing involuntary tics. In addition the reduced SAI indicates that impaired intracortical inhibition may not be limited to the motor cortex but also involves circuits linking sensory input and motor output. GTS with attention deficit hyperactivity disorder comorbidity is associated with more extensive changes in the excitability of motor cortex circuits than pure GTS or GTS+obsessive-compulsive disorder. The extent to which various different neuronal circuits are affected may be relevant for the phenotype of Tourette spectrum disorders.

Electrophysiological manifestations of stimulus evaluation, response inhibition and motor processing in Tourette syndrome patients

Gilles de la Tourette syndrome (GTS) is a neuropsychiatric disorder with childhood onset presenting with multiple fluctuating motor tics and one or more phonic tics. A significant proportion of people suffering from GTS are still symptomatic in adulthood and present other emotional and cognitive difficulties, along with motor problems that often accompany these comorbid conditions. The nature of these difficulties is still poorly understood and multiple comorbidities are often inadequately controlled. The current study investigates both stimulus evaluation and motor processing in GTS while controlling for comorbidity. Fifteen adults with GTS and 20 control participants were matched on gender, laterality and intelligence. The P300 component, the no-go anteriorization (NGA) as well as the stimulus and response-locked lateralized-readiness potentials (S-LRP, R-LRP) were elicited during a stimulus-response compatibility (SRC) paradigm. The standard version of the Stroop Color-Word Test (SCWT) was also administered. Reaction times showed that participants with GTS processed both the SRC and the SCWT more rapidly than the control group, while producing a delayed P300 peak latency. The GTS group also showed faster S-LRP onset in response to the incompatible and faster processing of interference in the SCWT. There was also a tendency toward a greater frontal shift of the NGA in the GTS group. The P300 latency showed that with GTS patients, stimulus evaluation occurs later whereas the overlapping pre-motor response selection processes occur faster. Our findings are congruent with a probable cortical motor over-activation hypothesis of GTS involving faster motor program selection in processing conflicting SR configuration.

Neurophysiological correlates of borderline personality disorder: a transcranial magnetic stimulation study

BACKGROUND

Cortical inhibition deficits have been demonstrated in several disorders with deficits in impulsive control (e.g., attention-deficit/hyperactivity disorder [ADHD], tic disorder, Tourette syndrome) by using transcranial magnetic stimulation (TMS). With borderline personality disorder (BPD), we investigated another disorder associated with high impulsivity by TMS. We hypothesized that BPD patients display decreased cortical inhibition and/or increased cortical excitation as assessed with TMS.

METHODS

Different inhibitory and excitatory TMS parameters were investigated in 19 unmedicated female BPD patients and 19 healthy control subjects matched for sex, age, handedness, and body height. Additionally, the results were controlled for ADHD symptomatology.

RESULTS

A reduced cortical silent period (CSP) duration was found in BPD patients compared with healthy control subjects in the right cortex. Even after controlling for ADHD symptoms, this result remained significant.

CONCLUSIONS

These findings support an association between BPD and cortical inhibition deficits as indexed through TMS. The results are discussed considering basic neurobiological mechanisms that may explain our findings of decreased intracortical inhibition in BPD patients.

Corticospinal system excitability at rest is associated with tic severity in tourette syndrome

BACKGROUND

Several measures of motor cortex excitability are abnormal in Gilles de la Tourette syndrome (GTS). However, it is not clear whether these represent abnormalities of specific pathways or reflect a more widespread reduction of motor cortex excitability. Their significance for the clinical phenotype is also unknown.

METHODS

We measured motor thresholds, input-output (I/O) curves, short interval intracortical inhibition (SICI), and cortical silent period (SP) with transcranial magnetic stimulation in 20 untreated GTS patients (12 uncomplicated, 4 with comorbid attention-deficit/hyperactivity disorder, 4 with comorbid obsessive-compulsive disorder) and 24 healthy subjects. Tics were rated with standard clinical scales and detailed video analysis.

RESULTS

Thresholds did not differ between groups. At rest, patients had shallower I/O curve slopes, despite their tics, and reduced SICI. Slopes were equal during voluntary muscle activation, as was the SP duration. Resting I/O slopes correlated, in uncomplicated GTS patients, most strongly to ratings of complex tics, hand and finger tics, and vocal tics, with shallower slopes predicting fewer tics. In complicated patients, good correlations were seen with neck/shoulder tics and vocal tics.

CONCLUSIONS

Corticospinal excitability in patients at rest is reduced. We suggest this is an adaptive response that may reduce release of unwanted movements.

Voluntary motor drive: possible reduction in Tourette syndrome

Electrophysiologically, Tourette syndrome (TS) is characterized by shortened cortical silent period (CSP), reflecting decreased motor inhibition. However, voluntary versus involuntary aspects of inhibitory functions in TS are not well understood. Hence, investigating voluntary motor drive (VMD) could help to elucidate this issue. A group of 14 healthy adolescents was compared with subjects of same age suffering from TS with (N = 6) and without (N = 6) presence of distal tics. Basic resting and active motor thresholds (RMT and AMT, respectively) as well as suprathreshold transcranial magnetic stimulation-conditioned RMT and AMT were determined during the CSP. The difference between AMT and RMT was considered as VMD quantum. No group-differences were found in RMT or AMT. Subjects with distal tics showed reduced VMD compared to healthy controls while patients without distal tics did not differ from controls. In the second half of CSP, patients with distal tics showed also diminished VMD compared to tic-patients without distal tics. The findings support the notion, that TS shows possible reduction of VMD and is associated with central motor threshold alterations confined to the very motor networks related to the tics observed.

Transcranial magnetic stimulation in children

Developmental disabilities (e.g. attention deficit disorder; cerebral palsy) are frequently associated with deviations of the typical pattern of motor skill maturation. Neurophysiologic tools, such as transcranial magnetic stimulation (TMS), which probe motor cortex function, can potentially provide insights into both typical neuromotor maturation and the mechanisms underlying the motor skill deficits in children with developmental disabilities. These insights may set the stage for finding effective interventions for these disorders. We review the literature pertaining to the use of TMS in pediatrics. Most TMS-evoked parameters show age-related changes in typically developing children and some of these are abnormal in a number of childhood-onset neurological disorders. Although no TMS-evoked parameters are diagnostic for any disorder, changes in certain parameters appear to reflect disease burden or may provide a measure of treatment-related improvement. Furthermore, TMS may be especially useful when combined with other neurophysiologic modalities (e.g. fMRI). However, much work remains to be done to determine if TMS-evoked parameters can be used as valid and reliable biomarkers for disease burden, the natural history of neurological injury and repair, and the efficacy of pharmacological and rehabilitation interventions.

Restoration of disturbed intracortical motor inhibition and facilitation in attention deficit hyperactivity disorder children by methylphenidate

BACKGROUND

Previous investigations using transcranial magnetic stimulation (TMS) have shown that neural inhibitory motor circuits are disturbed in ADHD children. We sought to investigate the influence of methylphenidate (MPH) on inhibitory and facilitatory motor circuits of ADHD children with TMS paired pulse protocols using surplus long interval inter-stimulus intervals (ISI) not investigated so far.

METHODS

Motorcortical modulation was tested with TMS paired pulse protocols employing ISI of 3, 13, 50, 100, 200, and 300 msec in 18 ADHD children before and on treatment with MPH. Clinical improvement by MPH was measured by the Conners score.

RESULTS

Analysis of variance (ANOVA) revealed a significant three-way interaction "Group x Amplitude x ISI," p = .001. Subsequent two-factorial ANOVAs and t-tests showed group specific differences of motor evoked potential (MEP) amplitudes for inhibitory ISIs of 3 and 100 msec, and for facilitatory ISIs of 13 and 50 msec. Compared to controls, an adjustment of these parameters by MPH could be shown. On MPH, a significant bivariate correlation was found between the Conners score reduction and averaged MEP amplitude changes only for inhibitory ISIs (3 and 100 msec).

CONCLUSIONS

In ADHD children, MPH modulates disturbed facilitatory and inhibitory motor circuits, which for the latter is associated with clinical improvement.

A subgroup of Tourette's patients overexpress specific natural killer cell genes in blood: a preliminary report

Gilles de la Tourette Syndrome (TS) is a heritable, neurodevelopmental disorder characterized by motor and vocal tics. As no single gene or region has emerged from standard linkage approaches, TS may result from several as-yet-unidentified genetic factors, and may also occur due to infection-triggered, autoimmune processes. Etiological or pathogenic differences might result in clinically indistinguishable TS subgroups. We have previously used whole genome human oligonucleotide microarrays in an attempt to identify patterns of gene expression in blood linked with TS. In this proof-of-principle study, we applied Principal Components Analysis to a previously collected set of 16 familial TS and 16 control blood samples to identify subgroups. Fourteen genes, primarily Natural Killer Cell (NK) genes, discriminated between TS and all controls. Granzyme B and NKG7 were confirmed using RT-PCR. Five probesets (four genes) reside in chromosomal regions previously linked to familial TS or obsessive-compulsive disorder. Using the 14 genes, a Principal Components Analysis as well as a cluster analysis identified a TS subgroup (n = 10/16) that overexpressed the NK genes. 7/10 subjects within this subgroup were diagnosed with attention-deficit hyperactivity disorder (ADHD), suggesting that this expression profile might be associated with TS and co-morbid ADHD. Principal Components Analysis of gene expression in blood may be useful for identifying subgroups of other complex neurodevelopmental diseases, and the gene expression profile identified in this study may provide a biomarker for at least one subgroup of heritable TS.

Atomoxetine treatment of ADHD in Tourette syndrome: reduction in motor cortex inhibition correlates with clinical improvement

OBJECTIVE

In children with attention deficit hyperactivity disorder (ADHD), clinical responses to the selective norepinephrine reuptake inhibitor atomoxetine (ATX) vary. We sought to determine in children with Tourette Syndrome (TS) whether clinical responses correlate with changes in short interval cortical inhibition (SICI).

METHODS

Fourteen children, ages 8-16, with ADHD and TS were treated open-label with ATX for one month. ADHD rating scale scores and SICI, measured with paired-pulse transcranial magnetic stimulation (pTMS), were assessed blindly and independently at treatment onset and one month later.

RESULTS

Eleven children, mean ADHD rating scale scores 31.8 (SD 8.2) at onset, completed the study. After one month, ADHDRS changes ranged from an increase of 4 points to a decrease (improvement) of 24 points (mean change -9.6, SD 9.1). The changes in ADHDRS scores correlated with reduction in SICI (r=.74, p=.010).

CONCLUSIONS

In children with TS, one month of atomoxetine treatment appears to induce correlated improvements in ADHD and, paradoxically, further reductions in cortical inhibition.

SIGNIFICANCE

PTMS-evoked SICI in ADHD with TS may be a biomarker of both deficiency and compensatory changes within cortical interneuronal systems. Effective atomoxetine treatment may augment compensatory processes and thereby reduce SICI.