Body Image Distortion and Cardio-Visual Integration in Anorexia Nervosa

Individuals diagnosed with anorexia nervosa (AN) often experience a distorted perception of their body size, known as body image distortion (BID). Despite its prevalence, the exact mechanisms underlying BID remain unclear, hampering the development of effective interventions. The allocentric lock hypothesis suggests that individuals with AN are locked in negative body memories due to inadequate integration of external sensory cues and internal body signals. While studies consistently highlight deficits in internal body perception (visceroception) among AN patients, the integration of visceroceptive and exteroceptive information remains insufficiently explored. This research project explores cardio-visual integration as a potential mechanism contributing to BID in AN. The first two studies investigated cardio-visual integration in a sample of AN patients. Study 1 examined the relative importance of visceral perception compared to cardio-visual integration in BID. Participants performed the heartbeat counting task to assess visceroception and the heartbeat discrimination task to indicate cardio-visual integration. Additionally, participants performed a metric body size estimation (BSE) task, estimating the circumference of their shoulders, waist, and hips. Contrary to expectations, results revealed no significant difference in BSE and heartbeat perception in both heartbeat perception tasks in AN patients compared to healthy controls. Cardio-visual integration was associated with BID in healthy controls but not in AN patients. Study 2 explored the impact of cardio-visual feedback on the visual processing of body images in AN patients and healthy controls. It was hypothesized that presenting body images synchronized with participants' heartbeats would influence visual event-related potentials (ERPs) recorded through electroencephalogram (EEG). The body-sensitive N170 component was expected to show differential mean amplitude between groups, picture orientation (intact and scrambled), and cardio-synchronicity (pictures presented synchronously vs delayed to participants' heartbeats). However, contrary to expectations, cardiac information did not modulate the visual processing of body images, and no group differences in vERPs were observed. Additionally, no difference in BID was found between AN patients and HCs, and cardio-visual vERPs were not associated with BID in either group. Study 3 explored the causal relationship between cardio-visual integration and BID using a cardio-visual full-body illusion in healthy adult women. Participants saw their own 3D body scan in virtual reality, flashing with an early (230ms) or late (530ms) delay after the participants' heartbeat or not flashing at all. A 3D object with the same three flashing conditions served as control conditions. Participants performed both a metric and a depictive BSE task before and after each illusion condition. EEG was recorded to measure to cortical processing of the heartbeat (HEP) as a potential mechanism to explain BSE change. Results indicated that body ownership was experienced in all body conditions regardless of cardiac feedback, while no body ownership was experienced in object conditions. Metric BSE improved after all illusion conditions, while depictive BSE remained stable and accurate. A reduced HEP amplitude was observed in both early delay conditions (body and object). However, whether the metric BSE changes resulted from the cardio-visual full-body illusion is questionable, as they were evident in all body and object conditions. In summary, the findings from the three studies do not support cardio-visual integration as an underlying mechanism of BID. Further investigation of multisensory integration across different sensory modalities and measurement levels in AN and its association with BID is warranted to develop a more precise understanding of BID and inform targeted intervention methods to improve prognosis in AN.