Body image during adolescence : behavioural and neuroimaging studies

The primary objective of this thesis was to investigate body image at both the behavioural and neural levels. We describe three studies aimed at: (1) developing a novel digital methodology with which to assess perceptual aspects of body image during adolescence; (2) investigating perceptual accuracy and sensitivity to changes in the size/shape of body images among healthy adolescents; and (3) identifying the neural mechanisms of body perception using functional magnetic resonance imaging (fMRI). A novel library of digital images of adolescent bodies was created and used to characterize natural covariations in body size and shape using principal components analysis. Identified principal components were used to morph body images in a realistic manner to generate larger or smaller bodies. These morphed body-image stimuli were then used in a behavioural investigation of self body-image perception among adolescents. Male and female adolescents overestimated the size of their bodies. When compared with males, females overestimated their body size to a greater extent and showed greater sensitivity in detecting changes in body size. Overestimation of body size and detection sensitivity increased with subject age. Detection sensitivity decreased as a function of subjects' body mass index (BMI). In order to identify the underlying neural mechanisms of these effects, functional block-design and fMR-adaptation experiments were completed in healthy young adults. During both experiments, females, and not males, showed greater fMR signal in the right versus left hemisphere in the extrastriate body area (EBA) and fusiform body area (FBA). During the block-design experiment, females also demonstrated greater right EBA response compared with males. Observer BMI modulated the EBA hemispheric effect in both experiments. A significant recovery from adaptation was found in EBA and FBA with body-image morphing, indicating that both regions were sensitive to body-size changes. Ultimately, we demonstrated the successful use of a novel body-morphing method for the assessment of body image, established that sex, age, and BMI modulate accuracy of self body-size estimation and detection of changes in body size, and described evidence of EBA and FBA as the likely neural substrates of these behavioural effects