Anorexia nervosa (AN) is one of the deadliest mental illnesses, with the highest mortality rate of any psychiatric disorder (Morris & Twaddle, 2007). It is an eating disorder characterized by immensely low body weight that results from placing extreme value on weight and physical shape. AN also leads to distorted body perception, as the continuous cycle of harmful, obsessive behaviors stems from a never-ending desire to be thin (Garner & Garfinkel, 1981-82). AN displays similar patterns to that of Body Dysmorphic Disorder (BDD), an increasingly common mental disorder, in which individuals excessively perceive themselves as flawed in appearance (Phillips, 2004). Both AN and BDD involve individual perceptions of body image, and recent research delving into this connection has discovered brain patterns linkages that may have significant implications for the future.
The way we perceive our world is largely due in part to the integration of various sensory signals in the brain to survive in our respective environments (Harris et al., 2015). The Weber Illusion explores the relationship between touch and vision, as well as the mental image of one’s body, and suggests that the density of receptors in an area plays a critical role in tactile stimulation. When testing the sensation of touch over equal distances, areas with high-density actually measured the same distances to be greater than low-density areas in addition to greater acuity for specific points of stimuli (Longo, Cardozo, & Haggard, 2008). However, receptor density is not consistent throughout the human body. This can be visually mapped out into a sensory homunculus, which acts as a neurological representation of receptor densities on the somatosensory cortex. Given that much of the sensations come from the upper part of the body, this is one of the many correlations between the abundant amounts of sensation from receptor density and the disproportionate predisposition of humans to view themselves as “top-heavy” (Fuentes, Longo, & Haggard, 2013). These complexities within the human body and its specific functions allude to the intricacies of studying visually-based disorders as AN and BDD.
Several lines of evidence suggest imbalances in the visual processing of individuals with AN and BDD, but there have been few direct comparisons of the neural reactions. A recent study attempted to look at brain activation and connectivity patterns in AN and BDD versus healthy individuals when looking at others’ bodies (Moody et al., 2020). There were 64 females between the ages of 13-30: 20 weight-restored AN, 23 BDD, and 21 healthy controls, all of which underwent the Mini International Neuropsychiatric Interview, a structured diagnostic interview to assess common mental health disorders, and BDD Diagnostic Module, a clinician-administered screening tool.
The research focused on 3 main networks: the dorsal visual network, a parietal network, and the striatal network. These are used in global image processing, body perception, and the reward system, respectively. While other systems are interconnected in visual processing, these three networks were selected due to previously studied connections with AN and BDD. The study also utilized different methods such as completing a “Bodies Task” that involved matching photos versus shapes, MRI echo-planar images, linear models to evaluate patterns, and independent components analysis to specifically gauge the temporally-related neuronal activation patterns.
The results can be categorized into activation and connectivity. Some of the shared patterns suggest that these disorders may be linked in ways that lead to anomalies in visual sensory processing and integrative systems. The dorsal visual and parietal networks used in visual processing of the body drastically differed in AN and BDD activation patterns, as BDD tended to show lower levels than controls, but there were regions with both greater and less activation than AN. This suggests that people with BDD tend to have reduced abilities to holistically integrate the senses and processing of spatial relationships. On the other hand, more similarities were found when it came to connectivity. While it’s difficult to straightforwardly interpret results, the lower activation and connectivity levels for AN compared to BDD point to AN being more consistent and having a greater intensity of body disorder symptoms.
Ultimately, the partially overlapping data in the networks of AN and BDD have great potential and clinical implications. Although nosological systems distinguish AN and BDD as separate disorders, the results of the study alongside previous studies continue to suggest partial similarities in the neurobiological processing of visual stimuli. The data also further supports the idea that visual processing aberrancies occur when those with AN and BDD view not just their own bodies, but also others as well. The combination of disorder-specific symptoms and similar neural patterns illustrate the complexities within neural activity and connectivity that may be the foundation for distorted perceptions. As research continues within the field of body dysmorphia and related diseases, we may be able to get closer to improving treatment and those affected by these deadly disorders.
Edited by Nivetha Aravind
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