Pointing to body parts: a double dissociation study.

Since Pick's seminal studies on autotopagnosia dating back to the beginning of last century, no agreement has been reached regarding the nature of the putative representations underlying the act of pointing to body parts. One influential account proposed the existence of a meta-representation, eventually organised as a module, specifically engaged in encoding spatial relationships of bodies. This body-specific representational level has been supposed to be equally involved in processing other persons' bodies as well as one's own. Here, we report two patients with dissociated performances in pointing to human body parts, thereby providing an interesting opportunity to discuss current models of body organisation. JR exhibited a selective deficit in pointing to his own body parts and a preserved ability to point to the parts of others. In contrast, AP demonstrated a selective inability to point to another person's body parts while her capacity to point to her own was intact. To further evaluate the level of body-specificity of AP's impairment, she underwent additional pointing tasks using non-human and human representations. AP's performances were close to those of control subjects across experiments, supporting the idea that processing the spatial layout of another person's body relies on a specific representational and neural system. Based on available data in the literature and the putative areas of lesion evidenced by cerebral blood flow studies in our two subjects, we hypothesise that left superior and inferior parietal regions are parts of networks involved in the respective processing of somatosensory and visuospatial representations of bodies.