Dewi Guardia, Aurélie Carey, Olivier Cottencin, Pierre Thomas, Marion Luyat

In anorexia nervosa (AN), body distortions have been associated with parietal cortex (PC) dysfunction. The PC is the anatomical substrate for a supramodal reference framework involved in spatial orientation constancy. Here, we sought to evaluate spatial orientation constancy and the perception of body orientation in AN patients. In the present study, we investigated the effect of passive lateral body inclination on the visual and tactile subjective vertical (SV) and body Z-axis in 25 AN patients and 25 healthy controls. Subjects performed visual- and tactile-spatial judgments of axis orientations in an upright position and tilted 90° clockwise or counterclockwise. We observed a significant deviation of the tactile and visual SV towards the body (an A-effect) under tilted conditions, suggesting a multisensory impairment in spatial orientation. Deviation of the Z-axis in the direction of the tilt was also observed in the AN group. The greater A-effect in AN patients may reflect reduced interoceptive awareness and thus inadequate consideration of gravitational inflow. Furthermore, marked body weight loss could decrease the somatosensory inputs required for spatial orientation. Our study results suggest that spatial references are impaired in AN. This may be due to particular integration of visual, tactile and gravitational information (e.g. vestibular and proprioceptive cues) in the PC.