Karim N'Diaye

Background: Cocaine addiction is a global health issue with limited therapeutic options and a high relapse rate. Attentional bias towards substance-related cues may be an important factor for relapse. However, it has never been compared in former and current cocaine-dependent patients. Methods: Attentional bias towards cocaine-related words was assessed using an emotional Stroop task in cocaine-dependent patients ( N = 40), long-term abstinent former cocaine-dependent patients ( N = 24; mean abstinence: 2 years) and control subjects ( N = 28). Participants had to name the colour of cocaine-related words, neutral words and colour names. We assessed response times using an automatic voice-onset detection method we developed and we measured attentional bias as the difference in response times between cocaine-related and neutral conditions. Results: There was an overall group effect on attentional bias towards cocaine, but no group effect on the colour Stroop effect. Two-by-two comparis...

L'objectif de ce travail a ete d'explorer les bases neurales de la perception du temps chez l'humain en analysant les correlats electromagnetiques du jugement temporel par reconstruction des generateurs corticaux du signal de scalp electroencephalographique et magnetoencephalographique. Dans deux articles experimentaux, nous montrons qu’independamment de la modalite sensorielle, un reseau etendu d'aires corticales est implique dans la discrimination de durees circaseconde et que le decours temporel de l'activite au sein de ce reseau s'accorde mal avec le mecanisme de pacemaker-accumulateur du modele de temps scalaire. Nous proposons donc dans un article theorique, co-ecrit avec Warren Meck, de montrer en quoi le modele Striatal Beat Frequency offre un cadre biologiquement plus realiste permettant de rapprocher les mecanismes a l'oeuvre dans la memoire de travail et dans le traitement temporel.

Checking behavior is a natural and adaptive strategy for resolving uncertainty in everyday situations. Here, we aimed at investigating the psychological drivers of checking and its regulation by uncertainty, in non-clinical participants and controlled experimental settings. We found that the sensitivity of participants’ explicit confidence judgments to actual performance (explicit metacognition) predicted the extent to which their checking strategy was regulated by uncertainty. Yet, a more implicit measure of metacognition (derived from asking participants to opt between trials) did not contribute to the regulation of checking behavior. Meanwhile, how participants scaled on questionnaires eliciting self-beliefs such as self-confidence and self-reported obsessive–compulsive symptoms also predicted participants’ uncertainty-guided checking tendencies. Altogether, these findings demonstrate that checking behavior is likely the outcome of a core explicit metacognitive process operating ...

Lack of behavioral flexibility has been proposed as one underlying cause of compulsions, defined as repetitive behaviors performed through rigid rituals. However, experimental evidence has proven inconsistent across human and animal models of compulsive-like behavior. In the present study, applying a similarly-designed reversal learning task in two different species, which share a common symptom of compulsivity (human OCD patients and Sapap3 KO mice), we found no consistent link between compulsive behaviors and lack of behavioral flexibility. However, we showed that a distinct subgroup of compulsive individuals of both species exhibit a behavioral flexibility deficit in reversal learning. This deficit was not due to perseverative, rigid behaviors as commonly hypothesized, but rather due to an increase in response lability. These cross-species results highlight the necessity to consider the heterogeneity of cognitive deficits in compulsive disorders and call for reconsidering the rol...

Checking behavior is a natural and adaptive strategy in uncertain situations. Here, we aimed at investigating the psychological drivers of checking and its regulation by uncertainty, in non-clinical participants and controlled experimental settings. We found that the sensitivity of participants’ explicit confidence judgments to actual performance (explicit metacognition) predicted the extent to which their checking strategy was regulated by uncertainty. This was, however, not the case of how participants used confidence to guide subsequent decision-making (implicit metacognition). Meanwhile, how participants scaled on questionnaires eliciting self-beliefs such as self-confidence and self-reported obsessive-compulsive symptoms also predicted participants’ uncertainty-guided checking tendencies. Altogether, these findings demonstrate that checking is likely the outcome of a core metacognitive process operating at the scale of single decisions, while remaining influenced by general sel...

ABSTRACTBackgroundCompulsive behaviors, one of the core symptoms of Obsessive-Compulsive Disorder (OCD), are defined as repetitive behaviors performed through rigid rituals. The lack of behavioral flexibility has been as being one of the primary causes of compulsions, but studies exploring this dimension have shown inconsistencies in different tasks performed in human and animal models of compulsive behavior. The aim of this study was so to assess the involvement of behavioral flexibility in compulsion, with a similar approach across different species sharing a common symptom of compulsivity.Methods40 OCD patients, 40 healthy individually matched control subjects, 26 C57BL/6J Sapap3 KO mice and 26 matched wildtype littermates were included in this study. A similar reversal learning task was designed to assess behavioral flexibility in parallel in these two species.ResultsWhen considered as homogeneous groups, OCD patients and KO mice expressing compulsive behaviors did not significa...

Metacognition is the high-level psychological processes that enable to monitor and control one’s own cognitive functioning, e.g. the confidence one has in a perceptual decision. Despite “pathological doubt” being a core feature of obsessive-compulsive disorder and repetitive checking, a common OCD symptom, being conceivable as an ill-founded attempt to accumulate evidence to restore confidence in one’s decisions, little is known on metacognition in OCD and how these processes may evolve through therapeutical interventions. In the present study, we explored metacognitive monitoring of perceptual decisions in severe resistant OCD patients, both in terms of quantitative behavioral markers, and in terms of their neural bases. We capitalized on a clinical trial assessing the efficacy of high-frequency deep brain stimulation of the subthalamic nucleus and the striatum to longitudinally assess patients on their metacognitive monitoring performance as they went through a cross-over design w...

Le trouble obsessionnel compulsif (TOC) est une pathologie fréquente, touchant 2 à 3 % de la population [1].L’implication de structures cortico-striato-thalamiques dans la symptomatologie du TOC est consensuellement reconnue [2]. Parmi elles, le cortex orbitofrontal (OFC), le cortex cingulaire antérieur (ACC) et le striatum ventral sont des structures d’un intérêt particulier dans les mécanismes de prises de décision associés au TOC.La mesure de la connectivité fonctionnelle basée sur l’IRM fonctionnelle (IRMf) permet d’étudier les liens fonctionnels entre plusieurs régions cérébrales [3]. Les études précédentes fournissant des résultats contradictoires sur la connectivité fonctionnelle dans le TOC entre le striatum ventral, l’OFC et le ACC [4], nous étudions la connectivité fonctionnelle basée sur l’IRMf chez 12 patients atteints de TOC de vérification (YBOCS > 16) contrastés avec 11 témoins enregistrés en « état de repos » (resting state) avec une séquence EPI sur une IRM 3 T (...

Le trouble obsessionnel compulsif (TOC) est une pathologie fréquente, touchant 2 à 3 % de la population [1].L’implication de structures cortico-striato-thalamiques dans la symptomatologie du TOC est consensuellement reconnue [2]. Parmi elles, le cortex orbitofrontal (OFC), le cortex cingulaire antérieur (ACC) et le striatum ventral sont des structures d’un intérêt particulier dans les mécanismes de prises de décision associés au TOC.La mesure de la connectivité fonctionnelle basée sur l’IRM fonctionnelle (IRMf) permet d’étudier les liens fonctionnels entre plusieurs régions cérébrales [3]. Les études précédentes fournissant des résultats contradictoires sur la connectivité fonctionnelle dans le TOC entre le striatum ventral, l’OFC et le ACC [4], nous étudions la connectivité fonctionnelle basée sur l’IRMf chez 12 patients atteints de TOC de vérification (YBOCS > 16) contrastés avec 11 témoins enregistrés en « état de repos » (resting state) avec une séquence EPI sur une IRM 3 T (CENIR, Institut du Cerveau et de la Moelle épinière, Paris). Notre analyse utilise l’OFC, le ACC et le striatum ventral comme régions d’intérêt (ROI), à partir de coordonnées définies dans une étude en IRMf précédemment menée dans notre laboratoire. Nous avons étudié la différence de connectivité entre ces régions deux à deux (ROI-to-ROI analysis) et entre ces régions et le reste du cortex (seed-voxel analysis).Nous souhaitons également étudier la corrélation entre la connectivité entre ces régions et la sévérité du TOC, mesurée avec l’échelle YBOCS.Nos données sont en cours d’analyse, mais des résultats préliminaires montrent une hypoconnectivité entre le striatum ventral droit et l’ACC chez les patients (p < 0,05). Ces résultats préliminaires nous orientent vers une poursuite de l’étude de la connectivité fonctionnelle dans le TOC, et notamment l’analyse de l’influence de différents paramètres cliniques (début des troubles, durée de la maladie, sous-type de TOC) sur cet aspect de la physiopathologie.

Contexte La thérapie cognitive et comportementale (TCC) est un traitement efficace pour soigner le trouble obsessionnel compulsif (TOC). Elle est connue pour induire des changements dans le métabolisme cérébral, mais la dynamique de ces changements et leur relation avec l’évolution clinique restent encore largement inconnues. Leur caractérisation représente une étape cruciale vers l’identification de biomarqueurs individualisés de réponse au traitement. Methods Nous avons procédé à l’évaluation clinique et à l’examen en IRMf de 35 patients atteints de TOC avant une TCC, à mi-thérapie (1,5 mois), à la fin (3 mois), ainsi que 6 mois après la fin de la thérapie. Pendant les examens en IRMf, nous avons utilisé une tâche originale d’exposition aux symptômes en utilisant trois types d’images : des images neutres, des images génériques induisant des obsessions et des images personnalisées induisant des obsessions. Résultats La TCC a entraîné une amélioration significative des symptômes obsessionnels compulsifs. La réponse à mi-thérapie s’est avérée être prédictive de l’amélioration finale (r2 = 0,67, p < 0,001). Initialement, les patients étaient plus sensibles aux images personnalisées qu’aux images génériques et neutres, ce en proportion avec de plus fortes activations dans le cortex cingulaire antérieur, le cortex orbitofrontal et pariétal. Dans le groupe de patients hauts-répondeurs (ΔYBOCS > 45 %), la sensibilité a été réduite à l’issue de la thérapie pour les images génériques et encore plus pour les images personnalisées. L’amélioration clinique a été associée avec une baisse de l’activité dans le cortex cingulaire antérieur et dans le cortex orbitofrontal gauche. Conclusion L’utilisation d’une tâche d’exposition novatrice et hautement sensible en IRMf montre que les symptômes et les marqueurs métaboliques ont des évolutions parallèles au cours de la TCC. Nos résultats, qui suggèrent que les premières séances de TCC sont cruciales, nous incitent à étudier les modifications anatomofonctionnelles qui sous-tendent les premières étapes de la thérapie.

IntroductionCognitive and Behavioral Therapy (CBT) is one of the two treatments recognized as most efficient to improve Obsessive Compulsive Disorder (OCD) symptoms.ObjectivesThe major aim of this study is to facilitate CBT for OCD checkers. To this purpose, we developed a new psycho-pedagogic tool to be used during CBT sessions and assessed its objective efficacy and the patients’ perception of their therapy.MethodologyExperimental CBT sessions included a “checking task”, composed of a “matching task” followed by a “checking phase” during which subjects were given the opportunity to check or to confirm their prior answer. This tool was appended to a classical CBT (as described in the literature).30 OCD patients with checking compulsions each followed 15 individual CBT sessions with a psychologist. They were randomized in two groups: a “reference CBT” (CBT classically described in literature) and an “experimental CBT” (reference CBT + checking task) group. Symptom severity was asses...

... temps Thèse présentée par Karim N'Diaye en vue de l'obtention du titre de ... Assessing the functional components of temporal processing through spatiotempo-ral imaging of cortical activity. Karim N'Diaye, Line Garnero, Viviane Pouthas. En préparation. ...

Background. Cognitive behavioural therapy (CBT) is a successful treatment of obsessive compulsive disorder (OCD). It is known to induce changes in cerebral metabolism; however, the dynamics of these changes and their relation to clinical change remain largely unknown, precluding the identification of individualized response biomarkers.
Method. In order to study the dynamics of treatment response, we performed systematic clinical and functional mag- netic resonance imaging (fMRI) evaluation of 35 OCD patients immediately before a 3-month course of CBT, halfway through and at its end, as well as 6 months after. To sensitize fMRI probing, we used an original exposure task using neutral, generic and personalized obsession-inducing images.
Results. As expected, CBT produced a significant improvement in OCD. This improvement was continuous over the course of the therapy; therefore, outcome could be predicted by response at mid-therapy (r2=0.67, p<0.001). Haemodynamic response to the task was located in the anterior cingulate and orbitofrontal cortices and was stronger during exposure to personalized obsession-inducing images. In addition, both the anxiety ratings and the haemo- dynamic response to the obsession-inducing images in the anterior cingulate and the left but not the right orbitofrontal clusters decreased with symptom improvement. Interestingly, haemodynamic activity continued to decrease after stabil- ization of clinical symptoms.
Conclusions. Using an innovative and highly sensitive exposure paradigm in fMRI, we showed that clinical and haemo- dynamic phenotypes have similar time courses during CBT. Our results, which suggest that the initial CBT sessions are crucial, prompt us to investigate the anatomo-functional modifications underlying the very first weeks of the therapy.

Facial expressions can be systematically coded using the Facial Action Coding System (FACS) that describes the specific action unit (AU) or combination of AUs elicited during different kinds of expressions. This study investigated the thermal patterns concomitant to specific action units performance. As thermal imaging can track dynamic patterns in facial temperature at any distance (>; 0.4 m), with high temporal (<; 20 m) and thermal (<; 20 mK@300 K) resolutions, this noninvasive technique was tested as a method to assess fluctuations of facial heat patterns induced by facial muscles contractions. Four FACS-trained coders produced nine different AUs or combination of AUs at various speeds and intensities. Using a spatial pattern approach based on PCA decomposition of the thermal signal, we showed that thermal fluctuations are specific to the activated AUs and are sensitive to the kinetics and intensities of AU production. These results open new avenues for studying patterns of facial muscle activity related to emotion or other cognitively induced activities, in a noninvasive manner, avoiding potential lighting issues.