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Published on: October 4, 2011
Functional Brain Mapping of Body Size Estimation Using a 3D Avatar
Hayden J Peel1,2, Joel P Diaz-Fong1,3,4, Sameena Karsan1
1Brain Health Imaging Centre, Centre for Addiction and Mental Health, Toronto, Ontario, Canada.
Background:
Body size estimation-the ability to judge the size and shape of one's own body-is a key perceptual component of body image. However, its neural basis, and the basis for inter-individual differences in accuracy, remain poorly understood, partly due to limitations in existing assessment tools.
Methods:
We developed Somatomap 3D, an interactive fMRI-compatible task allowing participants to manipulate a rotatable 3D avatar by adjusting the size and shape of 26 individual body parts to match their perceived body. Twenty-eight healthy male and female adults completed the task during fMRI. Brain activity in a priori regions of interest from previous studies of body processing was modeled using a general linear model incorporating event-specific parameters and parametric modulators related to task performance. Inter-individual differences in body size estimation accuracy were calculated using multidimensional scaling of body part estimation errors, and scores were correlated with BOLD signal eigenvariates from regions of interest.
Results:
Task engagement was associated with significant activation in hypothesized body-selective and multisensory regions, including bilateral extrastriate body area, right fusiform body area, right superior parietal lobule, and bilateral premotor cortex. Multidimensional scaling identified a primary subdimension reflecting distortions in body part girths, which was significantly associated with neural responses in the superior parietal lobule. No other brain regions showed significant associations with inter-individual differences in estimation accuracy.
Conclusions:
These results suggest that body size estimation engages a distributed network of visual, motor, and parietal regions. Among these, only the superior parietal lobule showed a significant association with inter-individual variation in body size estimation accuracy for body part girths, supporting its role as a candidate neural substrate for altered body representation in psychiatric conditions such as eating disorders and body dysmorphic disorder.
