Cognitive-pharmacologic functional magnetic resonance imaging in tourette syndrome: a pilot study

Brain functional connectivity in chronic tic disorders and Gilles de la Tourette syndrome

The pathophysiology of chronic tic disorder (cTD) and Gilles de la Tourette syndrome (GTS) is characterized by the dysfunction of both motor and non - motor cortico - striatal - thalamo - cortical (CSTC) circuitries, which leads to tic release and comorbids. A role of fronto - parietal network (FPN) connectivity breakdown has been postulated for tic pathogenesis, given that the FPN entertain connections with limbic, paralimbic, and CSTC networks. Our study was aimed at characterizing the FPN functional connectivity in cTD and GTS in order to assess the role of its deterioration in tic severity and the degree of comorbids. We recorded scalp EEG during resting state in patients with cTD and GTS. The eLORETA current source densities were analyzed, and the lagged phase synchronization (LPS) was calculated to estimate nonlinear functional connectivity between cortical areas. We found that the FPN functional connectivity in delta band was more detrimental in more severe GTS patients. Also, the sensorimotor functional connectivity in beta2 band was stronger in more severe cTD and GTS patients. FPN functional connectivity deterioration correlated with comorbids presence and severity in patients with GTS. Our data suggest that a FPN disconnection may contribute to the motoric symptomatology and comorbid severity in GTS, whereas sensorimotor disconnection may contribute to tic severity in cTD and GTS. Although preliminary, our study points out a differently disturbed brain connectivity between patients with cTD and GTS. This may serve as diagnostic marker and potentially interesting base to develop pharmacological and noninvasive neuromodulation trials aimed at reducing tic symptomatology.

P300 Source Localization Contrasts in Body-Focused Repetitive Behaviors and Tic Disorders

Tic disorders (TD) and body-focused repetitive behaviors (BFRB) have similar phenotypes that can be challenging to distinguish in clinical settings. Both disorders show high rates of comorbid psychiatric conditions, dysfunctional basal ganglia activity, atypical cortical functioning in the prefrontal and motor cortical regions, and cognitive deficits. Clinicians frequently confound the two disorders and it is important to find reliable objective methods to discriminate TD and BFRB. Neuropsychological tests and event-related potential (ERP) studies have yielded inconsistent results regarding a possible context updating deficit in TD and BFRB patients. However, most previous studies did not control for the presence of comorbid psychiatric condition and medication status, which might have confounded the findings reported to date. Hence, we aimed to investigate the psychophysiology of working memory using ERP in carefully screened TD and BFRB patients excluding those with psychiatric comorbidity and those taking psychoactive medication. The current study compared 12 TD patients, 12 BRFB patients, and 15 healthy control participants using a motor oddball task (button press). The P300 component was analyzed as an index of working memory functioning. Results showed that BFRB patients had decreased P300 oddball effect amplitudes over the right hemisphere compared to the TD and control groups. Clinical groups presented different scalp distributions compared to controls, which could represent a potential endophenotype candidate of BFRB and TD.

Levodopa effects on [ (11)C]raclopride binding in the resting human brain

Rationale: Synaptic dopamine (DA) release induced by amphetamine or other experimental manipulations can displace [ ¹¹C]raclopride (RAC*) from dopamine D2-like receptors. We hypothesized that exogenous levodopa might increase dopamine release at striatal synapses under some conditions but not others, allowing a more naturalistic assessment of presynaptic dopaminergic function. Presynaptic dopaminergic abnormalities have been reported in Tourette syndrome (TS).

Objective: Test whether levodopa induces measurable synaptic DA release in healthy people at rest, and gather pilot data in TS.

Methods: This double-blind crossover study used RAC* and positron emission tomography (PET) to measure synaptic dopamine release 4 times in each of 10 carbidopa-pretreated, neuroleptic-naïve adults: before and during an infusion of levodopa on one day and placebo on another (in random order). Five subjects had TS and 5 were matched controls. RAC* binding potential (BP _ND) was quantified in predefined anatomical volumes of interest (VOIs). A separate analysis compared BP _ND voxel by voxel over the entire brain.

Results: DA release declined between the first and second scan of each day (p=0.012), including on the placebo day. Levodopa did not significantly reduce striatal RAC* binding and striatal binding did not differ significantly between TS and control groups. However, levodopa’s effect on DA release differed significantly in a right midbrain region (p=0.002, corrected), where levodopa displaced RAC* by 59% in control subjects but increased BP _ND by 74% in TS subjects.

Discussion: Decreased DA release on the second scan of the day is consistent with the few previous studies with a similar design, and may indicate habituation to study procedures. We hypothesize that mesostriatal DA neurons fire relatively little while subjects rest, possibly explaining the non-significant effect of levodopa on striatal RAC* binding. The modest sample size argues for caution in interpreting the group difference in midbrain DA release with levodopa.

Tourette Syndrome: Complementary Insights from Measures of Cognitive Control, Eyeblink Rate, and Pupil Diameter

Some individuals with Tourette syndrome (TS) have severe motoric and vocal tics that interfere with all aspects of their lives, while others have mild tics that pose few problems. We hypothesize that observed tic severity reflects a combination of factors, including the degree to which dopaminergic (DA) and/or noradrenergic (NE) neurotransmitter systems have been affected by the disorder, and the degree to which the child can exert cognitive control to suppress unwanted tics. To explore these hypotheses, we collected behavioral and eyetracking data from 26 patients with TS and 26 controls between ages 7 and 14, both at rest and while they performed a test of cognitive control. To our knowledge, this is the first study to use eyetracking measures in patients with TS. We measured spontaneous eyeblink rate as well as pupil diameter, which have been linked, respectively, to DA and NE levels in the central nervous system. Here, we report a number of key findings that held when we restricted analyses to unmedicated patients. First, patients' accuracy on our test of cognitive control accounted for fully 50% of the variance in parentally reported tic severity. Second, patients exhibited elevated spontaneous eyeblink rates compared to controls, both during task performance and at rest, consistent with heightened DA transmission. Third, although neither task-evoked pupil dilation nor resting pupil diameter differed between TS patients and controls, pupil diameter was positively related to parentally reported anxiety levels in patients, suggesting heightened NE transmission in patients with comorbid anxiety. Thus, with the behavioral and eyetracking data gathered from a single task, we can gather objective data that are related both to tic severity and anxiety levels in pediatric patients with TS, and that likely reflect patients' underlying neurochemical disturbances.

Arterial spin labeling versus BOLD in direct challenge and drug-task interaction pharmacological fMRI

A carefully controlled study allowed us to compare the sensitivity of ASL (arterial spin labeling) and BOLD (blood oxygen level dependent) fMRI for detecting the effects of the adenosine A2a antagonist tozadenant in Parkinson disease. The study compared the effect of drug directly or the interaction of the drug with a cognitive task. Only ASL detected the direct effect of tozadenant. BOLD was more sensitive to the cognitive task, which (unlike most drugs) allows on–off comparisons over short periods of time. Neither ASL nor BOLD could detect a cognitive-pharmacological interaction. These results are consistent with the known relative advantages of each fMRI method, and suggest that for drug development, directly imaging pharmacodynamic effects with ASL may have advantages over cognitive-pharmacological interaction BOLD, which has hitherto been the more common approach to pharmacological fMRI.

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

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

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

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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.

Increased frontomotor oscillations during tic suppression in children with Tourette syndrome

This work investigated whether Tourette syndrome patients exhibit alterations in neural oscillations during spontaneous expression and suppression of tics. Electroencephalograms (EEGs) were recorded from 9 medication-naïve children with Tourette syndrome and 10 age-matched healthy subjects in resting conditions and during tic suppression. Their cortical oscillations were examined using the power spectral method and partial directed coherence. The authors found increased oscillations of broad frequency bands in the frontomotor regions of patients during tic expression, suggesting the involvement of aberrant cortical oscillations in Tourette syndrome. More significantly, prominent increases in theta oscillation in the prefrontal area and directed frontomotor interactions in the theta and beta bands were observed during tic suppression. Furthermore, the directed EEG interaction from the frontal to motor regions was positively correlated with the severity of tic symptoms. These findings suggest that the frontal to motor interaction of cortical oscillations plays a significant role in tic suppression.

A functional magnetic resonance imaging study of a large clinical cohort of children with Tourette syndrome

There is evidence that cortico-striato-thalamo-cortical pathways are involved in the pathophysiology of Tourette syndrome. During the performance of neuropsychological tests in subjects with Tourette syndrome there are suggestions for increased activity in the sensimotor cortex, supplementary motor areas, and frontal cortex. To replicate findings, the authors examined 22 medication-naive children with Tourette syndrome only, 17 medication-naive children with Tourette syndrome and comorbidity, and 39 healthy controls with functional magnetic resonance imaging (MRI). There were no differences in activation in brain regions between the children with Tourette syndrome (divided according to the presence of comorbidity) and healthy controls after correction for the confounders age, sex, and intelligence. Activation in the cingulated gyrus, temporal gyrus, and medial frontal gyrus was correlated significantly with obsessive-compulsive disorder score. The authors did not find significant correlations between activation patterns and age, sex, duration of disease, intelligence, severity of tics, and attention-deficit hyperactivity disorder (ADHD) score.

Functional neuroimaging in Tourette syndrome

Functional neuroimaging of neuropsychiatric disorders is a complex discipline requiring skills in medical science, philosophy, and technical physics. This review first examines the broad categories of functional imaging studies that have been utilized in this area, comparing the strengths and weaknesses of each approach. This review then looks at much of the available literature on functional imaging in Tourette syndrome (TS) and provides a synthesis of data. The review will also examine the different methodologies employed and will suggest which methodologies are most likely to lead to elucidation of the pathophysiology of TS and related conditions.

The management of tics

A tic is a stereotyped repetitive involuntary movement or sound, frequently preceded by premonitory sensations or urges. Most tic disorders are genetic or idiopathic in nature, possibly due to a developmental failure of inhibitory function within frontal-subcortical circuits modulating volitional movements. Currently available oral medications can reduce the severity of tics, but rarely eliminate them. Botulinum toxin injections can be effective if there are a few particularly disabling motor tics. Deep brain stimulation has been reported to be an effective treatment for the most severe cases, but remains unproven. A comprehensive evaluation accounting for secondary causes, psychosocial factors, and comorbid neuropsychiatric conditions is essential to successful treatment of tic disorders.

Microstructural abnormalities of striatum and thalamus in children with Tourette syndrome

We applied diffusion-tensor MRI (DT-MRI) to investigate directly the water diffusivity within subcortical gray matter structures comprising the fronto-striato-thalamic (FST) circuit, which is implicated in the pathophysiology of Tourette syndrome (TS). We investigated the structural integrity of basal ganglia and thalamus in 23 children with TS and 35 age-matched healthy controls (NC), and examined the association of DT-MRI measures to tic severity and comorbid symptoms. We measured parallel (lambda(1)) and perpendicular (lambda(23)) diffusivity, mean diffusivity (MD), and fractional anisotropy (FA) in both hemispheres. Compared with NC, the TS group showed a significant increase in lambda(1) (P = 0.003) and MD (P = 0.027) in the bilateral putamen, an increase in lambda(23) in right thalamus (P = 0.008), and a reversed asymmetry of FA (P = 0.03) in the thalamus. There was a significant positive correlation between lambda(23) in right thalamus and tic severity. TS patients showed significantly lower left caudate volume (P = 0.011) and bilateral thalamic volumes (left, P = 0.035, right P = 0.006) compared with NC. These findings support the notion that microstructural dysfunction measured by DT-MRI in component regions of the FST circuit contribute to the pathophysiology in TS.

Tourette syndrome and tic disorders: a decade of progress

OBJECTIVE

This is a review of progress made in the understanding of Tourette syndrome (TS) during the past decade including models of pathogenesis, state-of-the-art assessment techniques, and treatment.

METHOD

Computerized literature searches were conducted under the key words "Tourette syndrome," "Tourette disorder," and "tics." Only references from 1996-2006 were included.

RESULTS

Studies have documented the natural history of TS and the finding that tics usually improve by the end of the second decade of life. It has also become clear that TS frequently co-occurs with attention-deficit/hyperactivity disorder), obsessive-compulsive disorder, and a range of other mood and anxiety disorders. These comorbid conditions are often the major source of impairment for the affected child. Advances have also been made in understanding the underlying neurobiology of TS using in vivo neuroimaging and neurophysiology techniques. Progress on the genetic front has been less rapid. Proper diagnosis and education (involving the affected child and his or her parents, teachers, and peers) are essential prerequisites to the successful management of children with TS. When necessary, modestly effective antitic medications are available, although intervening to treat the comorbid attention-deficit/hyperactivity disorder and/or obsessive-compulsive disorder is usually the place to start.

CONCLUSIONS

Prospective longitudinal studies and randomized clinical trials have led to the refinement of several models of pathogenesis and advanced our evidence base regarding treatment options. However, fully explanatory models are needed that would allow for more accurate prognosis and the development of targeted and efficacious treatments.

Plasma level-dependent effects of methylphenidate on task-related functional magnetic resonance imaging signal changes

RATIONALE

Methylphenidate (MPH) is a dopamine and noradrenaline enhancing drug used to treat attentional deficits. Understanding of its cognition-enhancing effects and the neurobiological mechanisms involved, especially in elderly people, is currently incomplete.

OBJECTIVES

The aim of this study was to investigate the relationship between MPH plasma levels and brain activation during visuospatial attention and movement preparation.

METHODS

Twelve healthy elderly volunteers were scanned twice using functional magnetic resonance imaging (fMRI) after oral administration of MPH 20 mg or placebo in a within-subject design. The cognitive paradigm was a four-choice reaction time task presented at two levels of difficulty (with and without spatial cue). Plasma MPH levels were measured at six time points between 30 and 205 min after dosing. FMRI data were analysed using a linear model to estimate physiological response to the task and nonparametric permutation tests for inference.

RESULTS

Lateral premotor and medial posterior parietal cortical activation was increased by MPH, on average, over both levels of task difficulty. There was considerable intersubject variability in the pharmacokinetics of MPH. Greater area under the plasma concentration-time curve was positively correlated with strength of activation in motor and premotor cortex, temporoparietal cortex and caudate nucleus during the difficult version of the task.

CONCLUSION

This is the first pharmacokinetic/pharmacodynamic study to find an association between plasma levels of MPH and its modulatory effects on brain activation measured using fMRI. The results suggest that catecholaminergic mechanisms may be important in brain adaptivity to task difficulty and in task-specific recruitment of spatial attention systems.