La lésion fonctionnelle dans la conversion hystérique : des aliénistes à l’imagerie cérébrale

Abstract

Recent progress in functional imagery confirmed the intuition of the 19th century French alienists who introduced, before Charcot, the concept of “functional lesion” applied to hysterical conversion. Neural mechanism underlying conversion paralysis has been more particularly studied in recent years using these new tools. Distinct patterns of brain activation have been elicited in healthy subjects simulating weakness and conversion paralysis. Several brain areas are over-activated in conversion paralysis when compared to healthy subjects: prefrontal cortex, precuneus, anterior cingulate cortex, amygdala. These results, not only confirm that conversion must be distinguished from malingering, they also provide new insights on the neural mechanisms of conversion paralysis. The activation of regions associated to the default mode network such as the precuneus and the ventral prefrontal cortex could reflect an increase in self-monitoring or motor imagery. The involvement of limbic regions like the anterior cingulate cortex and the amygdala suggest disturbed influence of emotional processes over motor execution. In the second part of this study, we report the results of brain structural and functional explorations performed in a case of chronic left conversion paralysis. The abnormal involvement of the precuneus is discussed together with the possible transition from functional to organic lesion in chronic paralysis. Simultaneous presence of sensory impairment and more remarkably left spatial neglect emphasize the singularity of each case and the necessary caution that should be taken for the interpretation of brain images. From a therapeutic point of view, these data could provide some new theoretical basis for rehabilitation and the use of brain stimulation techniques.