De l'autotopoagnosie à un modèle de représentations des connaissances du corps

Abstract

Body knowledge can break down in a variety of ways after brain damage. In this article some of these disruptions traditionally associated with left parietal lesion are reviewed. At the beginning of the 20th century, Pick first described autotopoagnosia as an inability to indicate parts of the own body whereas the ability to denominate is preserved. Some years later, Gerstmann introduced the notion of finger agnosia which is the main element of Gerstmann's syndrome (finger agnosia, agraphia, acalculia and left-right confusion). More recently, heterotopoagnosia has been defined as a selective inability to point to another person's body parts while the capacity to point to one's own is intact. Clinical manifestations, cognitive performances and neuroanatomical correlations are exposed and linked.These perturbations are very rare, at least in the pure form (without anomia, apraxia, visuo-spatial or global cognitive dysfunction).They are constant, affecting bilateral parts of the body, without any impact on the daily living. Based on the cases in the literature, the specificity of autotopoagnosia is discussed across different hypotheses. Autotopoagnosia has either been attributed to pure fiction or to a language impairment or to the inability to analyse a whole into its parts. During the last 20 years, further single case studies with circumscribed lesion without aphasia have reported that autotopoagnosia cannot be reduced to a non-specific cognitive disorder. Several accounts propose that autotopoagnosia reflects a human body-specific knowledge impairment. Moreover, implications from the dissociation of disturbed designation and preserved lexico-semantic representations in autotopoagnosia are integrated in a model of the organisation of the body knowledge with multiple levels of representations. The first contains semantic and lexical information about body parts, such as names and functional relationships, strongly linked to the verbal system. The second contains the category-specific visuospatial representations of bodies, such as the structural description of the body, the position and the proximity of the body parts, more strongly linked to the non-verbal visual and somatic sensory systems. The third is a body-reference system that provides a dynamic and actual body image, emerging from various sources of sensory afferences. Finally, motor representations participate to the construction and maintenance of the somatosensory representations. It is proposed that autotopoagnosia is an impairment which predominantly affects body-specific visuospatial representations. Finally, neuroimaging data are suggestive of dysfunction originating in the left dominant parietal regions.