Abnormal lateralization of fine motor actions in Tourette syndrome persists into adulthood.

Youth with Tourette syndrome (TS) exhibit, compared to healthy, abnormal ability to lateralize digital sequential tasks. It is unknown whether this trait is related to inter-hemispheric connections, and whether it is preserved or lost in patients with TS persisting through adult life. We studied 13 adult TS patients and 15 age-matched healthy volunteers. All participants undertook: 1) a finger opposition task, performed with the right hand (RH) only or with both hands, using a sensor-engineered glove in synchrony with a metronome at 2 Hz; we calculated a lateralization index [(single RH-bimanual RH)/single RH X 100) for percentage of correct movements (%CORR); 2) MRI-based diffusion tensor imaging and probabilistic tractography of inter-hemispheric corpus callosum (CC) connections between supplementary motor areas (SMA) and primary motor cortices (M1). We confirmed a significant increase in the %CORR in RH in the bimanual vs. single task in TS patients (p<0.001), coupled to an abnormal ability to lateralize finger movements (significantly lower lateralization index for %CORR in TS patients, p = 0.04). The %CORR lateralization index correlated positively with tic severity measured with the Yale Global Tic Severity Scale (R = 0.55;p = 0.04). We detected a significantly higher fractional anisotropy (FA) in both the M1-M1 (p = 0.036) and the SMA-SMA (p = 0.018) callosal fibre tracts in TS patients. In healthy subjects, the %CORR lateralization index correlated positively with fractional anisotropy of SMA-SMA fibre tracts (R = 0.63, p = 0.02); this correlation was not significant in TS patients. TS patients exhibited an abnormal ability to lateralize finger movements in sequential tasks, which increased in accuracy when the task was performed bimanually. This abnormality persists throughout different age periods and appears dissociated from the transcallosal connectivity of motor cortical regions. The altered interhemispheric transfer of motor abilities in TS may be the result of compensatory processes linked to self-regulation of motor control.

"De-novo" consultation: Evaluation of an outpatient's clinic dedicated to early diagnosis of parkinsonian syndromes.

INTRODUCTION: In the absence of specific clinical signs, imaging or biomarkers, the differential diagnosis of degenerative parkinsonian syndromes may be difficult at early stages of the disease. To reduce the risk of misdiagnosis or delayed diagnosis and referral to multiple medical centers at disease onset, easier access to expert centers should be available. To improve the initial care of parkinsonian patients, the Parkinson's disease Expert Center (PEC) at Pitié-Salpêtrière Academic Hospital has set up a specific outpatients clinic with short waiting times dedicated to the diagnosis of early Parkinson's disease and related disorders. METHODS: The PEC setup first identifies requests for diagnostic confirmation of parkinsonian syndromes, then specific outpatients clinic visits are scheduled weekly, with examinations carried out by neurologists at the PEC on a rotating schedule. Data from the first year of the new procedure were analyzed retrospectively through self-administered questionnaires sent to patients seen during this period. The main outcomes were to confirm the ability to keep to short delays for patients' examinations and to assess patients' satisfaction with the setup. RESULTS: Both study outcomes were achieved. The creation of an outpatients clinic dedicated to the early diagnosis of parkinsonian syndromes allowed shorter delays before the first examination of 5 weeks instead of several months. Keeping to the weekly schedule and limited time taken for each visit was also achieved. Following this initial outpatients visit, diagnosis of a parkinsonian syndrome was clinically confirmed or further specified in 80% of cases. A survey of patients' satisfaction showed a rate of over 91% in terms of the timing and course of clinical examinations at our PEC. DISCUSSION/CONCLUSION: This study of our quality-improvement program for Parkinson's disease management has shown that specific consultations with shorter waiting times aiming to allow early specialized assessment of parkinsonian syndromes is beneficial for patients and reduces the risk of delayed diagnoses.

Valence-dependent influence of serotonin depletion on model-based choice strategy.

Human decision-making arises from both reflective and reflexive mechanisms, which underpin goal-directed and habitual behavioural control. Computationally, these two systems of behavioural control have been described by different learning algorithms, model-based and model-free learning, respectively. Here, we investigated the effect of diminished serotonin (5-hydroxytryptamine) neurotransmission using dietary tryptophan depletion (TD) in healthy volunteers on the performance of a two-stage decision-making task, which allows discrimination between model-free and model-based behavioural strategies. A novel version of the task was used, which not only examined choice balance for monetary reward but also for punishment (monetary loss). TD impaired goal-directed (model-based) behaviour in the reward condition, but promoted it under punishment. This effect on appetitive and aversive goal-directed behaviour is likely mediated by alteration of the average reward representation produced by TD, which is consistent with previous studies. Overall, the major implication of this study is that serotonin differentially affects goal-directed learning as a function of affective valence. These findings are relevant for a further understanding of psychiatric disorders associated with breakdown of goal-directed behavioural control such as obsessive-compulsive disorders or addictions.

Motivation and value influences in the relative balance of goal-directed and habitual behaviours in obsessive-compulsive disorder.

Our decisions are based on parallel and competing systems of goal-directed and habitual learning, systems which can be impaired in pathological behaviours. Here we focus on the influence of motivation and compare reward and loss outcomes in subjects with obsessive-compulsive disorder (OCD) on model-based goal-directed and model-free habitual behaviours using the two-step task. We further investigate the relationship with acquisition learning using a one-step probabilistic learning task. Forty-eight OCD subjects and 96 healthy volunteers were tested on a reward and 30 OCD subjects and 53 healthy volunteers on the loss version of the two-step task. Thirty-six OCD subjects and 72 healthy volunteers were also tested on a one-step reversal task. OCD subjects compared with healthy volunteers were less goal oriented (model-based) and more habitual (model-free) to reward outcomes with a shift towards greater model-based and lower habitual choices to loss outcomes. OCD subjects also had enhanced acquisition learning to loss outcomes on the one-step task, which correlated with goal-directed learning in the two-step task. OCD subjects had greater stay behaviours or perseveration in the one-step task irrespective of outcome. Compulsion severity was correlated with habitual learning in the reward condition. Obsession severity was correlated with greater switching after loss outcomes. In healthy volunteers, we further show that greater reward magnitudes are associated with a shift towards greater goal-directed learning further emphasizing the role of outcome salience. Our results highlight an important influence of motivation on learning processes in OCD and suggest that distinct clinical strategies based on valence may be warranted.

Impulsivity in disorders of food and drug misuse.

BACKGROUND: Evidence suggests some overlap between the pathological use of food and drugs, yet how impulsivity compares across these different clinical disorders remains unclear. Substance use disorders are commonly characterized by elevated impulsivity, and impulsivity subtypes may show commonalities and differences in various conditions. We hypothesized that obese subjects with binge-eating disorder (BED) and abstinent alcohol-dependent cohorts would have relatively more impulsive profiles compared to obese subjects without BED. We also predicted decision impulsivity impairment in obesity with and without BED. METHOD: Thirty obese subjects with BED, 30 without BED and 30 abstinent alcohol-dependent subjects and age- and gender-matched controls were tested on delay discounting (preference for a smaller immediate reward over a larger delayed reward), reflection impulsivity (rapid decision making prior to evidence accumulation) and motor response inhibition (action cancellation of a prepotent response). RESULTS: All three groups had greater delay discounting relative to healthy volunteers. Both obese subjects without BED and alcohol-dependent subjects had impaired motor response inhibition. Only obese subjects without BED had impaired integration of available information to optimize outcomes over later trials with a cost condition. CONCLUSIONS: Delay discounting appears to be a common core impairment across disorders of food and drug intake. Unexpectedly, obese subjects without BED showed greater impulsivity than obese subjects with BED. We highlight the dissociability and heterogeneity of impulsivity subtypes and add to the understanding of neurocognitive profiles across disorders involving food and drugs. Our results have therapeutic implications suggesting that disorder-specific patterns of impulsivity could be targeted.

Disorders of compulsivity: a common bias towards learning habits.

Why do we repeat choices that we know are bad for us? Decision making is characterized by the parallel engagement of two distinct systems, goal-directed and habitual, thought to arise from two computational learning mechanisms, model-based and model-free. The habitual system is a candidate source of pathological fixedness. Using a decision task that measures the contribution to learning of either mechanism, we show a bias towards model-free (habit) acquisition in disorders involving both natural (binge eating) and artificial (methamphetamine) rewards, and obsessive-compulsive disorder. This favoring of model-free learning may underlie the repetitive behaviors that ultimately dominate in these disorders. Further, we show that the habit formation bias is associated with lower gray matter volumes in caudate and medial orbitofrontal cortex. Our findings suggest that the dysfunction in a common neurocomputational mechanism may underlie diverse disorders involving compulsion.

[Basal ganglia and psychiatric disorders: an experimental validation]. / Troubles psychiatriques et ganglions de la base : une validation expérimentale.

Abnormal movements and behavioral disorders are characteristic manifestations observed in certain neuropsychiatric diseases such as Tourette's syndrome or Huntington Disease. Together with brain imaging findings, the clinical data could suggest a relationship with basal ganglia dysfunction. In the first part of this review, we recall the anatomic relationships existing, via segregated cortico-cortical circuits, between these structures and the cortical areas having motor and cognitive or motivational-emotional attributes. This structure suggests that in pathologies like Parkinson's or Huntington disease cognitive and motivational-emotional disorders as well motor disturbances could be related to lesions or dysfunctions involving individual or combined zones of the basal ganglia. The second part of the paper focuses on a description of the various methodologies used to explore these relationships: behavioral, anatomic and brain imaging methods are used in non-human primate models in order to reproduce motor and behavioral disturbances and to determine the neuronal circuits involved. Microinjection of bicucullin into the external globus pallidus has been found to induce localized and reversible neuronal activation. Abnormal movements can be obtained from the motor territory of the external globus pallidus whereas hyperactivity with attentional deficit or stereotypies have been obtained from the associative or limbic territory of the same structure. In the striatum, the same pharmacological activation can induce either abnormal movements from motor and associative functional territories or behavioural changes with hyperactivity or, on the contrary, hypoactivity from associative functional territory with stereotyped behavior and sexual manifestations when the microinjections were done in the limbic striatum. Anatomic studies as well as brain imaging using PET confirm the involvement of segregated anatomic pathways through the basal ganglia in behavioral as well as motor disorders.