Corollary Discharge Failure in an Oculomotor Task Is Related to Delusional Ideation in Healthy Individuals

International audiencePredicting the sensory consequences of saccadic eye movements likely plays a crucial role in planning sequences of saccades and in maintaining visual stability despite saccade-caused retinal displacements. Deficits in predictive activity, such as that afforded by a corollary discharge signal, have been reported in patients with schizophrenia, and may lead to the emergence of positive symptoms, in particular delusions of control and auditory hallucinations. We examined whether a measure of delusional thinking in the general, non-clinical population correlated with measures of predictive activity in two oculomotor tasks. The double-step task measured predictive activity in motor control, and the in-flight displacement task measured predictive activity in trans-saccadic visual perception. Forty-one healthy adults performed both tasks and completed a questionnaire to assess delusional thinking. The quantitative measure of predictive activity we obtained correlated with the tendency towards delusional ideation, but only for the motor task, and not the perceptual task: Individuals with higher levels of delusional thinking showed less self-movement information use in the motor task. Variation of the degree of self-generated movement knowledge as a function of the prevalence of delusional ideation in the normal population strongly supports the idea that corollary discharge deficits measured in schizophrenic patients in previous researches are not due to neuroleptic medication. We also propose that this difference in results between the perceptual and the motor tasks may point to a dissociation between corollary discharge for perception and corollary discharge for action

Preserved subliminal processing and impaired conscious access in schizophrenia.

BACKGROUND: Studies of visual backward masking have frequently revealed an elevated masking threshold in schizophrenia. This finding has frequently been interpreted as indicating a low-level visual deficit. However, more recent models suggest that masking may also involve late and higher-level integrative processes, while leaving intact early bottom-up visual processing. OBJECTIVE: To test the hypothesis that the backward-masking deficit in schizophrenia corresponds to a deficit in the late stages of conscious perception, whereas the subliminal processing of masked stimuli is fully preserved. DESIGN: Twenty-eight patients with schizophrenia and 28 normal control subjects performed 2 backward-masking experiments. We used Arabic digits as stimuli and varied quasi-continuously the interval with a subsequent mask, thus allowing us to progressively unmask the stimuli. We finely quantified their degree of visibility using objective and subjective measures to evaluate the threshold duration for access to consciousness. We also studied the priming effect caused by the variably masked numbers in a comparison task performed on a subsequently presented and highly visible target number. RESULTS: The threshold delay between the digit and mask necessary for the conscious perception of the masked stimulus was longer in patients compared with controls. This higher consciousness threshold in patients was confirmed by an objective and a subjective measure, and both measures were highly correlated for the patients and controls. However, subliminal priming of masked numbers was effective and identical in patients and controls. CONCLUSIONS: Access to conscious report of masked stimuli is impaired in schizophrenia, whereas fast bottom-up processing of the same stimuli, as assessed by subliminal priming, is preserved. These findings suggest a high-level origin of the masking deficit in schizophrenia, although they leave open for further research its exact relation to previously identified bottom-up visual processing abnormalities

Brain Dynamics Underlying the Nonlinear Threshold for Access to Consciousness

When a flashed stimulus is followed by a backward mask, subjects fail to perceive it unless the target-mask interval exceeds a threshold duration of about 50 ms. Models of conscious access postulate that this threshold is associated with the time needed to establish sustained activity in recurrent cortical loops, but the brain areas involved and their timing remain debated. We used high-density recordings of event-related potentials (ERPs) and cortical source reconstruction to assess the time course of human brain activity evoked by masked stimuli and to determine neural events during which brain activity correlates with conscious reports. Target-mask stimulus onset asynchrony (SOA) was varied in small steps, allowing us to ask which ERP events show the characteristic nonlinear dependence with SOA seen in subjective and objective reports. The results separate distinct stages in mask-target interactions, indicating that a considerable amount of subliminal processing can occur early on in the occipito-temporal pathway (<250 ms) and pointing to a late (>270 ms) and highly distributed fronto-parieto-temporal activation as a correlate of conscious reportability

Anomalies de l'accès à la conscience dans la schizophrénie (étude d'un paradigme de masquage visuel rétrograde)

La schizophrénie est une pathologie psychiatrie invalidante du sujet jeune dont la complexité des manifestations cliniques et les mécanismes étiopathogéniques demeurent encore une énigme pour la connaissance médicale. Le développement récent des neurosciences cognitives a permis l'exploration de cette pathologie à partir d'autres points de vue, complémentaires des approches neurobiologiques et de celles plus classiques de la psychiatrie fondées sur la classification clinique. Déterminer la localisation et le niveau des anomalies existant dans la schizophrénie est un objectif essentiel de ce nouveau champ de recherche. Des anomalies sensorielles précoces de " bas niveau " ont notamment été postulées : celles-ci pourraient avoir pour conséquence des dysfonctionnements cognitifs à un niveau plus tardif et intégratif. En particulier, les études du masquage rétrograde visuel révélant un seuil de conscience plus élevé dans la schizophrénie ont été interprétées comme indicatives d'un déficit visuel précoce. Néanmoins, des approches théoriques et expérimentales plus récentes suggèrent que le processus de masquage visuel pourrait également être lié à des processus attentionnels de plus haut niveau. Nous décrivons ici les résultats d'une expérience originale de psychologie expérimentale réalisée chez 28 patients schizophrènes montrant un seuil d'accès à la conscience plus élevé chez les patients que chez les sujets contrôles alors que l'amorçage subliminal des stimuli masqués était identique dans les deux groupes. Ces résultats suggèrent que ce déficit de masquage dans la schizophrénie pourrait correspondre à un déficit des étapes tardives de la perception consciente alors que les étapes visuelles précoces non conscientes des stimuli masqués sont préservées. Ces données sont compatibles avec un déficit plus général dans la schizophrénie du contrôle et de l'intégration consciente, potentiellement en rapport avec des anomalies de connectivité neuronale à longue distance.PARIS7-Xavier Bichat (751182101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

L' accès à la conscience et ses perturbations dans la schizophrénie (étude des mécanismes cognitifs et cérébraux du masquage visuel rétrograde)

PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Délire et toxoplasmose (revue de la bibliographie)

La physiopathologie des schizophrénies (sens anglo-saxon) demeure à ce jour méconnue, et l'existence de cas de psychoses apparaissant secondairement à des pathologies cérébrales organiques peut constituer un éclairage intéressant sur la physiopathologie des schizophrénies primaires. Dans le groupe hétérogène des psychoses organiques, la revue de la littérature rapporte quelques spécificités sémiologiques, l'existence de lésions cérébrales comme étiologie et les lobes temporaux comme localisation préférentielle. Un cas clinique présentant un syndrome délirant paranoïaque contemporain d'une toxoplasmose cérébrale est détaillé. Seul le traitement antiparasitaire, associé aux psychotropes, a permis un enkystement du délire. Des modifications comportementales en lien avec la toxoplasmose sont connues chez la souris, ayant pour probable origine une modulation de la neurotransmission (notamment Toxoplama Gonddi produit une enzyme très proche de la tyrosine hydroxylase), la localisation cérébrale des kystes et la modulation immunitaire. Par ailleurs, on décrit une forte séroprévalence à Toxoplama Gondii chez les patients schizophrènes et certains auteurs évoquent que le parasite puisse faire partie des facteurs étiologiques de la maladie.PARIS13-BU Serge Lebovici (930082101) / SudocSudocFranceF

Illusory displacement due to object substitution near the consciousness threshold

A briefly presented target shape can be made invisible by the subsequent presentation of a mask that replaces the target. While varying the target–mask interval in order to investigate perception near the consciousness threshold, we discovered a novel visual illusion. At some intervals, the target is clearly visible, but its location is misperceived. By manipulating the mask’s size and target’s position, we demonstrate that the perceived target location is always displaced to the boundary of a virtual surface defined by the mask contours. Thus, mutual exclusion of surfaces appears as a cause of masking