Study: fMRI reveals functional differences in autistic patients
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| Functional MRI scans show activations associated with motor imagery as compared with spatial imagery tasks. Image source: New England Journal of Medicine |
“We know the two hemispheres must work together for many brain functions,” explained lead author Jeffery S. Anderson, MD, PhD, from the department of neuroradiology at the University of Utah School of Medicine in Salt Lake City. “We used MRI to look at the strength of these connections from one side to the other in autism patients,” he said, theorizing that reduced long-range functional connectivity may point to autism.
Anderson and colleagues used fMRI to construct spatial maps of the right and left hemispheres of 53 adolescent and young adult males diagnosed with high-functioning autism spectrum disorder (ASD). The authors matched these patients to a control group of 39 typically developing males of the same age group. Resting-state blood oxygen levels of all subjects were examined and cross-correlation curves of pairs of corresponding voxels in each hemisphere were constructed.
The researchers determined that interhemispheric correlation specific to regions with functional relevance to autism was significantly reduced in patients with ASD. The researchers observed significant connectivity differences in the sensorimotor cortex, anterior insula, fusiform gyrus, superior temporal gyrus and superior parietal lobule, which are associated with functions such as motor skills, attention, facial recognition and social functioning. The mean correlation between the connected voxels in the control group was .253, while the mean for the ASD cohort scored significantly lower at .232 (p=.023).
Unlike in ASD, covariate analyses controlling for subjects’ handedness, language skills, IQ and other neuropsychological metrics revealed no significant differences in interhemispheric connectivity. The authors suggested that structural and functional metrics measured different aspects of interhemispheric connectivity, as no direct relationship was observed between corpus callosal volume and gray matter interhemispheric connectivity, despite both being significantly reduced in patients with autism.
The authors also discovered that interhemispheric correlation connectivity decreased with age in the typically developing group. For the autistic group, developmental differences in interhemispheric connectivity continued into early adulthood.
The authors acknowledged that limiting their study to high-functioning young autistic males restricted their findings from being extended to females, younger children or lower-function ASD patients. Nevertheless, Anderson and colleagues emphasized that “Our finding adds to growing evidence that abnormalities of interhemispheric connectivity in autism are widespread but regionally specific and related to cognitive and neurological impairments commonly found in the disorder.”
The authors posited that their findings highlight MRI as a potential tool to assist physicians in diagnosing and treating autism.