As far as general wiring goes, the brains of neurotypical individuals is fairly standardized. This is not the case for those diagnosed with Autism Spectrum Disorder (ASD). Some studies have found that ASD brains have higher connectivity, while conflicting studies have concluded that they have fewer connections. A new study might be able to reconcile those opposing results, as it has found that ASD brains are not only wired differently from neurotypical brains, but have a number of idiosyncrasies when compared to one another as well. This could help explain behaviors at different points on the autism spectrum. Avital Hahamy of the Weizmann Institute of Science in Israel is lead author of the paper, which was published in Nature Neuroscience.
The study utilized functional magnetic resonance imaging (fMRI) scans of resting individuals who were either neurotypical or diagnosed with ASD. The researchers drew on five large data sets obtained from the Autism Brain Imaging Data Exchange (ABIDE) database. The scans revealed the relative inter-hemispheric connectivity of different brain regions; that is, connections spanning both halves of the brain.
"Resting-state brain studies are important because that is when patterns emerge spontaneously, allowing us to see how various brain areas naturally connect and synchronize their activity,” Hahamy said in a press release.
The inter-hemispheric connectivity for different regions of neurotypical brains appeared to be standardized. The frontal and temporal cortices, responsible for executive decision making, generally had reduced connectivity. Connectivity across the brain is increased in the occipital and sensorimotor cortices, where the majority of sensory and motor processing occurs. Scan after scan, the neurotypical brains showed uniform patterns in relative connectivity.
Examining the ASD brains, however, was not as straightforward. While they all had some areas with over- or under-connectivity compared to the neurotypical brains, the regions where these occurred varied for every individual. There wasn’t much of a pattern when the scans were looked at as a group, but when an individual’s scan was compared to their list of ASD-related symptoms, very clear correlations were seen.
“The magnitude of an individual's pattern distortion in homotopic inter-hemispheric connectivity correlated significantly with behavioral symptoms of ASD,” the authors wrote in the paper. “We propose that individualized alterations in functional connectivity organization are a core characteristic of high-functioning ASD, and that this may account for previous discrepant findings [of previous studies].”
Furthermore, this divergence from neurotypical patterning might have been sparked by ASD, and then solidified by a sort of positive feedback loop.
"From a young age, the average, typical person's brain networks get molded by intensive interaction with people and the mutual environmental factors,” Hahamy continued. “Such shared experiences could tend to make the synchronization patterns in the control group's resting brains more similar to each other. It is possible that in ASD, as interactions with the environment are disrupted, each one develops a more uniquely individualistic brain organization pattern.”
The research is still early and the issue needs to be investigated much more thoroughly before connections to the individualized anomalies and symptoms can be discussed with any authority. In the future, this could be used as a diagnostic tool for early intervention, or possibly lead to new treatments.