So, a study just published in the Proceedings of the National Academy of Sciences uses fMRI to compare the neural response to biological motion in three groups of subjects: people with autism, unaffected siblings of people with autism, and a control group, who have neither autism nor family members with autism. This is a fairly standard sort of thing to do when people study disorders that, like autism, have high heritability, and therefore presumably a significant genetic component. There were some interesting findings in this paper, though, that make it stand out. In particular, the authors identify a set of brain regions that show elevated activity specifically in the group of unaffected siblings, and call these “compensatory” regions.
The idea is this. People with autism have a set of genetic variants that give them a predisposition for developing autism. Straightforward, right? Presumably, the siblings of people with autism carry many of these same genetic variants, but there is some reason why they don’t develop the disorder. Of course, one possibility is that they do not, in fact, carry the autism-causing genetic variants. Another possibility, raised by this paper, is that they do have genes that predispose them to autism, but that some compensatory mechanism has maintained normal neural development in the face of this genetic predisposition. This compensation could be developmental – in that some sort of canalization mechanism sets in when it somehow senses that brain development is going off track. Or, it could be genetic, in that the unaffected siblings also possess genetic variants (presumably at other genetic loci) that shift them back towards normal development.
Here’s Figure 3 from the paper. The top panel shows the “state” regions. Those are brain regions that show differential activation in the autism group (reduced activity in response to viewing biological motion). The middle panel shows the “trait” regions, which are the regions with reduced activity in both the autism group and the group of unaffected siblings. The bottom panel shows the “compensatory” regions, which show elevated activity specifically in the group of unaffected siblings.
The brain regions identified as “state” regions are those that are typically identified as regions of reduced activity in autism – a nice validation. The two “compensatory” regions are the right posterior superior temporal sulcus (pSTS) and ventromedial prefrontal cortex (vmPFC). Both of these regions have been associated with social perception and cognition. Note that both of these regions also appear in the “state” category.
So what does that mean? Well, that means that there are certain regions within these two structures that show reduced activity in cases of autism. There are other regions within the same two structures that are not impaired in autism, but show enhanced activity in unaffected siblings.
Like much of the most interesting science, this paper raises more questions than it answers, and there are many conceivable explanations of these patterns. The results suggest a number of interesting avenues for future research, however.
The paper can be found here. It is an open-access article, so you don’t need a subscription to PNAS to get it.
Update: Full citation
Kaiser MD, Hudac CM, Shultz S, Lee SM, Cheung C, Berken AM, Deen B, Pitskel NB, Sugrue DR, Voos AC, Saulnier CA, Ventola P, Wolf JM, Klin A, Vander Wyk BC, & Pelphrey KA (2010). Neural signatures of autism. Proceedings of the National Academy of Sciences of the United States of America PMID: 21078973