Peripersonal Space representation in Anorexia Nervosa: an experimental evaluation

Background and aim of the study Anorexia nervosa (AN) is a complex psychiatric disorder characterized by body image distortion and fear of gaining weight, with multifactorial causes, including genetic and psychological factors. Body image distortion is central to AN, with perceptual and cognitive-affective components. Peripersonal space (PPS), the area surrounding the body, is influenced by multisensory information and individual factors. This study investigates the relationship between AN and PPS, examining whether alterations in body perception in AN are reflected in PPS representation. The aim is to measure the Facilitation Index, assessing differences in the processing of multimodal stimuli and the correlation with clinical variables, including the relationship between PPS and BMI. Methods The study recruited 39 women with AN and 54 healthy women. Participants completed questionnaires and tests, including the Eating Disorder Examination Questionnaire (EDE-Q), the Liebowitz Social Anxiety Scale (LSAS), the Figure Rating Scale (FRS), and the Preferred Interpersonal Distance Scale. They then performed a virtual reality PPS task using a VR headset and ExpyVR software. Participants responded to tactile stimuli while viewing visual stimuli approaching (cubes or faces). Reaction rates (RT) were measured in different conditions (bimodal, unimodal tactile, unimodal visual). For the analysis of PPS data, outliers in RT were excluded. A multisensory facilitation index was calculated by subtracting the mean unimodal RT from the mean bimodal RT for each distance. For statistical analysis, R study and independent samples t-test were used to compare groups and repeated measures ANOVA was used to assess PPS. Spearman correlations were also performed to analyze the relationships between clinical variables and PPS. Results Repeated measures ANOVA analysis revealed a significant main effect of distance (F = 110.47, p < .001), indicating that reaction times increase with increasing distance. However, no significant differences were found between the AN and HC groups, nor between the stimulus presentation conditions. Correlation analyses, conducted using the mean slope and intercept values across neutral and social conditions, revealed that height was not correlated with PPS, as expected. In healthy controls, a negative correlation was observed between BMI, weight, and PPS, indicating that as weight increases, PPS tends to “shrink.” Furthermore, in controls, subjectively perceived BMI showed the same negative correlation with PPS. In contrast, in AN patients, only perceived BMI correlated with PPS, but in the opposite direction compared to controls. AN patients who reported higher perceived BMI, greater body distortion, and greater body dissatisfaction showed higher slope values, indicative of less segregation between peripersonal and extrapersonal space. These associations differed significantly from those observed in the control group, which exhibited an opposite pattern across all these variables and a significant negative correlation between body dissatisfaction and slope. Healthy controls also showed a positive association between their actual BMI and the intercept, hence participants with higher BMI had a less extensive PPS. Conclusions In conclusion, the study suggests that distorted body perception in AN is associated with an altered representation of PPS, indicating a link between self-perception and the representation of surrounding space. This study represents a starting point toward a greater understanding of the relationships between AN, PPS, and body perception. Therefore, further research is needed in the future to further explore these findings investigate the underlying neurobiological mechanisms, and determine how therapeutic interventions targeting body perception may also influence the representation of peripersonal space.