The New York Times Magazine recently ran a cover article about mapping the connectome, all of the connections that link all of the neurons in someone's brain. Many of these connections are formed and reinforced as a result of our experiences, and their sum total constitutes everything about our personalities: the memories we've formed, the skills we've learned, the passions that drive us.

There is even data suggesting that some neurological disorders are in fact "connectopathies," characterized by either aberrant connections or an unusual extent of connections among neurons. Some studies have found that autism spectrum disorder (ASD) is associated with decreased functional connectivity in the brain, but other experiments have found increased connectivity in autistic brains. A new study may have reconciled these contradictory findings. Researchers at the Weizmann Institute of Science in Israel determined that brain regions with high interconnectivity in controls have reduced connectivity in ASD, and regions with lower connectivity in controls have elevated connectivity in people with ASD.

The scientists analyzed fMRI scans from high functioning autistic adults and controls, obtained from five different data sets. When the scans from the controls were superimposed upon each other, a typical, canonical template of connectivity was clear. Certain regions had high inter hemispheric (between the right and left sides) connectivity: primary sensory-motor regions like the sensorimotor cortex and the occipital cortex. Others showed low interhemispheric connectivity: regions like the frontal cortex and temporal cortex, which are involved in higher order association. Overall, the control brain scans looked pretty much the same as each other.

Autistic brains, in contrast, were all different. Each had regions of high and low connectivity, and there were regions whose connectivity was increased relative to controls and those that were decreased. But no standard template emerged; when these scans were superimposed one atop the another, no distinct areas of high and low connectivity were discernible.

This comparison of grouped brain scans, rather than just the individual ones, revealed that the unusual pattern in the connectivity of ASD brains is due to the topology of their connectivity patterns and not necessarily the strength or weakness of any given connections. It also revealed that people with ASD have more individualized, idiosyncratic connectivity patterns than controls do. Each autistic brain differed from the norm, but each did so in its own way. The researchers couldn't even find subgroups of ASD brains that were similar to each other, although they noted that larger data sets might uncover some of these.

Autism is diagnosed not by anatomical criteria, but by deficits in social and language abilities and excessive repetitive behaviors. When the researchers checked if the level of disturbance in the connectivity pattern correlated with an individual's behavioral symptoms, they found that this was precisely the case.

This effect, just like the degree of connectivity pattern distortion, was most pronounced for homotopic interhemispherical connections—those that went from a specific location on one side of the brain to the corresponding location in the other hemisphere. But it was seen to a lesser extent for connections between different regions of the brain, whether on the same or different sides. This connectivity pattern distortion, in contrast, did not correlate with IQ scores.

Since the study did not include children, the authors were not sure when or how these effects might develop—if they have developmental origins, or are some sort of compensatory mechanisms that occurs later in life. They did note that the idiosyncrasies did not seem to stem from anatomical differences in autistic brains, as they did not have significantly atypical shapes or significantly asymmetrical hemispheres.

An intriguing possibility is that, because neural connections are shaped by the routine behaviors and experiences that we have every day, people with ASD each exhibit idiosyncratic connectivity patterns in their brains because they each experience the world and interact with their environment in an idiosyncratic way. Their idiosyncratic behaviors prevent them from engaging in the typical interactions that create typical brain scans.

Nature Neuroscience, 2014. DOI: 10.1038/nn.3919 (About DOIs).