Neuroimagerie de l’insight dans la schizophrénie : revue de la littérature

RésuméLe concept d’insight en psychiatrie a soulevé de nombreuses réticences et a fait l’objet d’approches diverses tant d’un point de vue conceptuel que méthodologique. De grands progrès ont été effectués suite à la mise au point d’échelles psychométriques spécifiques qui permettent une évaluation plus précise et quantifiée de la notion. Dans la schizophrénie, l’altération de l’insight est considérée comme l’une des caractéristiques les plus fréquentes qui conditionne la prise en charge diagnostique et thérapeutique du patient. Une meilleure compréhension de la neurobiologie du déficit d’insight pourrait aider au développement de nouvelles stratégies thérapeutiques ciblant l’insight. Les progrès de la recherche en neuroscience sur les corrélats cérébraux de l’insight sont avérés utiles pour sa compréhension. Dans cette perspective, la neuroanatomie de l’insight dans la schizophrénie, les détails de la connectivité anatomique et fonctionnelle par rapport à différentes dimensions de l’insight commencent à produire des résultats importants. Un regard exhaustif de la littérature de la neuroimagerie de l’insight dans la schizophrénie est un but majeur de cette revue. Les recherches en imagerie structurelle ont permis dans un premier temps le repérage des anomalies macroscopiques en relation avec le déficit d’insight dans différentes aires cérébrales, en particulier les aires frontales, temporales et pariétales, et on mit en évidence par la suite une asymétrie hémisphérique en relation avec le déficit d’insight dans la schizophrénie (la plupart des anomalies cérébrales concernent la partie droite). D’autres études témoignent aussi de l’importance du cortex préfrontal surtout dorsolatéral, du cortex cingulaire, de l’insula, du précuneus et du cervelet dans l’accès à l’insight chez les patients schizophrènes. Il faut cependant noter que la représentation cérébrale des différentes dimensions de l’insight pourrait avoir un support commun mais aussi un support particulier, comme le suggèrent certains auteurs. Toutes ces données sont en faveur d’une étiologie neurologique de l’insight dans la schizophrénie. Il est à signaler que le déficit d’insight cognitif n’a bénéficié que de deux investigations en imagerie cérébrale et qui ont montré l’implication du cortex préfrontal dorsolatéral et de l’hippocampe. Par conséquent, il apparaît prématuré de proposer un modèle anatomique de l’insight cognitif dans la schizophrénie. Des études supplémentaires demeurent nécessaires pour mieux comprendre les relations causales entre les anomalies cérébrales et la dégradation de l’insight dans la schizophrénie.

ObjectivesInsight in psychiatry has been defined and conceptualized in a number of ways but none of them was found to be self-explanatory. There has been an exponential rise in studies of insight, in part accelerated by the availability of several psychometric scales for measuring insight. Lack of insight has been associated in schizophrenia with low treatment adherence, a high number of relapses, increased number of hospital admissions, and subsequently poorer psychological and cognitive functioning. For this reason, there is considerable interest in understanding the underlying neural mechanisms of insight, which may have important implications for the development of future insight-oriented neuro-psychiatric treatment. Neuroimaging may be considered an important technique to help understand the anatomical, functional and metabolic neurocircuitry underlying poor insight in schizophrenia. Growing neuroimaging research provides evidence for underlying brain impairment in insight deficits in schizophrenia. In order to expose a panoramic view to the readers, this article reviews the neuroimaging studies conducted to date, which have investigated the neural bases of insight in schizophrenia.MethodsElectronic searches were performed in PubMed, PsycINFO, Sciencedirect and Web of Science databases, using the following keywords: Imaging; neuroimaging; Positron Emission Tomography (PET); spectroscopy; functional Magnetic Resonance Imaging (fMRI); structural Magnetic Resonance Imaging (MRI); Single Photon Emission Computed Tomography (SPECT); Voxel Based Morphometry (VBM); Diffusion Tensor Imaging (DTI); Computed Tomography (CT); Insight; schizophrenia; awareness of illness. Searches were also performed from the references of the systematic review articles on neurobiological correlates of insight in schizophrenia. Animal studies and single case reports were excluded. Twenty-five articles were selected for the present review. From these; 12 used structural MRI; 6 used VBM; 3 used fMRI; 2 used CT; 1 used DTI and 1 used VBM combined to DTI.ResultsThe search showed that studies in this area were published recently and that the neuroanatomic substrate of insight in schizophrenia has not yet been consolidated. This inconsistency could arise from the complex nature of insight and the use of a variety of insight assessments. Most of the studies analyzed in this review used structural neuroimaging techniques to assess brain abnormalities associated with poor insight. The functional neuroanatomy of insight has only recently been investigated and to our knowledge, there are only 3 studies that have examined brain activity with fMRI in relation to insight in schizophrenia.ConclusionThis review investigated the neural deficiencies underlying poor insight in schizophrenic patients. In spite of methodological differences among studies, results provide evidence of structural and functional brain abnormalities in frontal, parietal and temporal region related to insight deficits. Some studies have found a hemispheric asymmetry in relationship to poor in insight (the majority of brain abnormalities concern the right hemisphere). In addition, growing research indicated that the prefrontal cortex, particularly the dorsolateral prefrontal cortex, the anterior cingulated cortex, the insula, the precuneus and the cerebellum can also underlying insight in schizophrenia. It is interesting to mention that some authors have suggested that each dimension of insight can be specifically linked to certain brain structures. Taking together, data on the neuropsychological and neuroanatomical correlates of clinical insight suggested that lack of insight in schizophrenia could be conceived as a neurocognitive deficit, analogously to anosognosia in brain injury and dementia. On the contrary, to date, the neuroanatomical correlates of cognitive insight have been scarcely studied. Only two studies reported that Self-reflectiveness was positively related to gray matter volume of the right ventro-lateral prefrontal cortex, the BCIS composite index was positively correlated with total left hippocampal volume, and Self-certainty was inversely correlated with bilateral hippocampal volumes. However, it is important to note that neuroimaging research on cognitive insight in schizophrenia is in a preliminary, and the results on this are inconclusive. Further research is needed to better understand the causal relationships between brain abnormalities and degradation of insight in schizophrenia.