Mémoire de source – présentation générale et revue des études dans la schizophrénie. [Source monitoring: general presentation and review of literature in schizophrenia]

International audienceSOURCE MONITORING FRAMEWORK: Source monitoring refers to the ability to remember the origin of information. Three source monitoring processes can be distinguished: external source monitoring, internal or self-monitoring and reality monitoring (i.e. discrimination between internal and external sources of information). Source monitoring decisions are based on memory characteristics recorded such as perceptions, contextual information or emotional reactions and heuristic or more controlled judgement processes. BRAIN STRUCTURES: Several studies suggested that specific structures in the prefrontal and the mediotemporal lobes are the main areas implicated in source monitoring. ASSESSMENT: A typical source monitoring paradigm includes an items generation stage and a second stage of recognition of items (old versus new) and identification of their sources: external (usually the examiner) or internal (the subject). Several indices can be calculated based on the raw data such as the number of false alarms, attribution biases or discrimination indexes. To date, there is no standardized source monitoring task and differences in the type of items used (words, pictures), in the cognitive or emotional effort involved or in the delay between the two test stages, contribute to the heterogeneity of results. FACTORS INFLUENCING SOURCE MONITORING: Factors such as age (either very young or very old) and emotions influence source monitoring performances. Influence of gender was not properly explored, whereas the role of IQ and selective attention is still debated. SOURCE MONITORING DEFICITS IN NEUROLOGICAL DISORDERS: Source monitoring deficits are observed mainly in disorders affecting frontotemporal areas, such as frontal trauma, Alzheimer's disease or frontotemporal dementia. SOURCE MONITORING AND SCHIZOPHRENIA: Source monitoring errors (e.g. external misattribution of self-generated information) are observed in schizophrenia and seem to correlate with positive symptomatology, in particular auditory hallucinations, thought intrusion and alien control symptoms. These results are of particular interest in clinical research because source monitoring is one of the rare cognitive tests showing a correlation with the positive dimension. Source monitoring deficits have been proposed as a potential explanation for the positive symptoms and some, but not all studies lent support to this hypothesis. Heterogeneity of studied samples, in particular different criteria to define hallucinating subjects (e.g. currently versus anytime during their lives), could explain the discordant results. SOURCE MONITORING IN PSYCHIATRIC DISORDERS WITHIN THE SCHIZOPHRENIC SPECTRUM: Source monitoring impairments were observed in pharmacological models of psychosis, in first degree relatives of schizophrenic patients, and also in the general population associated with schizotypal dimensions. These results support a relationship between source monitoring deficits and some of the symptomatic dimensions of the schizophrenic spectrum but still await replication. SOURCE MONITORING AND OTHER PSYCHIATRIC DISORDERS: Some studies found source monitoring deficits in other psychiatric conditions such as mania or obsessive-compulsive disorder. Thus, those studies suggest that source monitoring deficits may be not specific to schizophrenia. CONCLUSION: Source monitoring competencies are critical for good (i.e. adapted) everyday functioning. Source monitoring deficits have been suggested as a potential explanation for some (or all) positive psychotic symptoms. However, to date, methodological inconsistencies (especially with regard to test design and choice of subjects' samples) have precluded firm, definite conclusions

Phase equilibria in metastable regime in the (C8H12NO)2[ZnCl4] ferroelectric system

(C8H12NO)2[ZnCl4] is an interesting ferroelectric organic-inorganic hybrid compound that shows a complex structural phase diagram, investigated in this work by X-ray diffraction and differential scanning calorimetry, characterized by an irreversible transition occurring on heating at 390 K, and coupled with successive transformations taking place on cooling in a metastable regime. The basic structural transition, leading from a monoclinic P21to an orthorhombic P212121symmetry and involving the doubling of the unit cell volume, is associated with an order-disorder transformation of the 4-methoxybenzylammonium cations coupled with a reorientation of tetrachloridozincate anions. During cooling, the cationic order and the monoclinic symmetry are progressively restored, but the doubling of the original cell volume is maintained by the alternate canting of adjacent cationic layers. It is noteworthy that all the polymorphs preserve the non-centric nature of the structure, but the ferroelectric behavior, characterized by high saturation polarization PS= 17 μC cm-2and relatively low coercive field EC= 8 kV cm-1, is lost in the transition on heating and not recovered at low temperature when the original polar P21symmetry is restored