Electrophysiological Correlates of Proactive Control and Binding Processes during Task Switching in Tourette Syndrome.

The occurrence of tics in Tourette syndrome (TS) has often been linked to impaired cognitive control, but empirical findings are still inconclusive. A recent view proposes that tics may be the result of an abnormally strong interrelation between perceptual processes and motor actions, commonly referred to as perception-action binding. The general aim of the present study was to examine proactive control and binding effects in the context of task switching in adult human patients with TS and matched healthy controls. A cued task switching paradigm was employed in 24 patients (18 male, 6 female) and 25 controls while recording electroencephalography (EEG). Residue iteration decomposition (RIDE) was applied to analyze cue-locked proactive cognitive control and target-locked binding processes. Behavioral task switching performance was unaltered in patients with TS. A cue-locked parietal switch positivity, reflecting proactive control processes involved in the reconfiguration of the new task did not differ between groups. Importantly, target-locked fronto-central (N2) and parietal (P3) modulations, reflecting binding processes between perception and action, differed between groups. Underlying neurophysiological processes were best depicted after temporal decomposition of the EEG signal. The present results argue for unaltered proactive control but altered perception-action binding processes in the context of task switching, supporting the view that the integration of perception and action is processed differently in patients TS. Future studies should further investigate the specific conditions under which binding may be altered in TS and the influence of top-down processes, such as proactive control, on bindings.

Temporal discounting in adolescents and adults with Tourette syndrome.

Tourette syndrome is a neurodevelopmental disorder associated with hyperactivity in dopaminergic networks. Dopaminergic hyperactivity in the basal ganglia has previously been linked to increased sensitivity to positive reinforcement and increases in choice impulsivity. In this study, we examine whether this extends to changes in temporal discounting, where impulsivity is operationalized as an increased preference for smaller-but-sooner over larger-but-later rewards. We assessed intertemporal choice in two studies including nineteen adolescents (age: mean[sd] = 14.21[±2.37], 13 male subjects) and twenty-five adult patients (age: mean[sd] = 29.88 [±9.03]; 19 male subjects) with Tourette syndrome and healthy age- and education matched controls. Computational modeling using exponential and hyperbolic discounting models via hierarchical Bayesian parameter estimation revealed reduced temporal discounting in adolescent patients, and no evidence for differences in adult patients. Results are discussed with respect to neural models of temporal discounting, dopaminergic alterations in Tourette syndrome and the developmental trajectory of temporal discounting. Specifically, adolescents might show attenuated discounting due to improved inhibitory functions that also affect choice impulsivity and/or the developmental trajectory of executive control functions. Future studies would benefit from a longitudinal approach to further elucidate the developmental trajectory of these effects.

Local and Global Changes in Brain Metabolism during Deep Brain Stimulation for Obsessive-Compulsive Disorder.

Recent approaches have suggested that deep brain stimulation (DBS) for obsessive-compulsive disorder relies on distributed networks rather than local brain modulation. However, there is insufficient data on how DBS affects brain metabolism both locally and globally. We enrolled three patients with treatment-refractory obsessive-compulsive disorder with ongoing DBS of the bilateral ventral capsule/ventral striatum. Patients underwent resting-state 18F-fluorodeoxyglucose and positron emission tomography in both stimulation ON and OFF conditions. All subjects showed relative hypometabolism in prefronto-basal ganglia-thalamic networks compared to a healthy control cohort when stimulation was switched OFF. Switching the stimulation ON resulted in differential changes in brain metabolism. Locally, volumes of activated tissue at stimulation sites (n = 6) showed a significant increase in metabolism during DBS ON compared to DBS OFF (Mean difference 4.5 % ± SD 2.8; p = 0.012). Globally, differential changes were observed across patients encompassing prefrontal increase in metabolism in ON vs. OFF condition. Bearing in mind limitations of the small sample size, we conclude that DBS of the ventral capsule/ventral striatum for obsessive-compulsive disorder increases brain metabolism locally. Across distributed global networks, DBS appears to exert differential effects, possibly depending on localization of stimulation sites and response to the intervention.

Neuronal correlates of delay discounting in healthy subjects and its implication for addiction: an ALE meta-analysis study.

BACKGROUND: Delay discounting (DD) describes the phenomenon of devaluing future rewards in favor of immediate rewards. Increased DD is a key behavioral marker of addiction, and has been suggested as a target for interventions to alleviate addiction symptoms (e.g., preference for immediate drug use over larger-and-later rewards, and relapses) in patients with substance use disorders (SUD). OBJECTIVES: Performed a meta-analysis on neuroimaging results of DD regarding specific contrasts in healthy participants. Reviewed the results of existing patient studies in light of the meta-analyses results. METHODS: We conducted activation likelihood estimation meta-analyses on DD neuroimaging studies (25 studies, n = 583; 354 males and 229 females) regarding six analytic strategies. RESULTS: The meta-analyses revealed various subdivisions of the cortical-basal ganglia circuits that are associated with different aspects of DD in healthy subjects. By comparing the meta-analyses results and patients' studies regarding each contrast, we highlighted three brain regions that may underlie excessive DD in patients. Decreased left inferior frontal gyrus (IFG) activity was related to less preference for delayed choices; reduced ventral striatum (VS) activity was associated with impaired valuation processes; and declined anterior cingulate cortex (ACC)/medial prefrontal cortex (mPFC) activity was associated with alterations in processing difficult choices. CONCLUSIONS: We propose that neuromodulation (e.g. deep brain simulation) or behavioral interventions (e.g. episodic future imagination) targeting these key brain regions (IFG, VS, ACC/mPFC) may be effective for improving DD function in patients with SUD, enhancing valuations of future rewards and helping to resist the temptation of immediate drug use.