Differences in Frontal-Posterior Activity during Mental Rotation of Body-Related Stimuli in Autism Spectrum Disorders

Background: Cognitive and behavioral studies in recent years have identified visuospatial processing as a generally intact area of functioning in individuals with autism spectrum disorders (ASD). Previous research suggests that this advantage may be reflected in tasks, such as mental rotation. However, mental rotation of body-related stimuli in ASD has received little attention relative to rotation of objects and shapes.

Objectives: This study investigates (a) the neural mechanisms underlying mental rotation of sensorimotor stimuli and (b) the extent to which autistic traits and symptomology play a role in processing mental rotation.

Methods: Thirteen children and adolescents with ASD and 15 age-and-IQ-matched typically developing (TD) control participants took part in this fMRI study. Participants completed a mental rotation task while fMRI data were acquired using a Siemens 3.0 Tesla Allegra head-only scanner. In this task, images of two hands appeared on a computer screen, one on the left and one on the right side of a crosshair. Participants were asked to press a button if the rotated hand on the right panel (rotated either 45° or 90°) was the same hand as the hand shown on the left panel. Imaging analysis included brain activation, change in percent signal intensity, and functional connectivity, along with correlation analyses involving these measures and behavioral assessment and self-report scores.

Results: Preliminary analyses indicate that the ASD group was significantly more accurate, relative to TD group, in mental rotation [F(1,696) = 31.75, p<0.01], although this effect was related to their spatial skills, measured by performance IQ. When 45° rotation was contrasted with that of 90° rotation, the ASD group showed greater activation, relative to TD group, in the right fusiform gyrus (FG), left and right middle occipital lobe, and right precuneus. The TD group, on the other hand, showed greater activation in left inferior frontal gyrus (LIFG), left medial prefrontal cortex (MPFC), left supplementary motor area (LSMA), and left anterior cingulate cortex (ACC) (p<0.005, k=144). ASD participants also showed intact functional connectivity during this mental rotation task.

Conclusions: While participants with autism performed the mental rotation task as well as or better than the TD controls, it was accompanied by differences in brain activity. The ASD participants seem to have relied more on visuospatial and body related areas (increased activity in FG, occipital, and precuneus), whereas TD participants recruited frontal areas (increased activity in MPFC, SMA, LIFG). It is possible that there is strategic difference between the groups in approaching this task, perhaps bottom-up versus top-down processing. This variation in approach may underlie difficulties observed in individuals with ASD when faced with more complex social stimuli requiring visual-perspective taking or full-body rotations and warrants continued and future investigations.