>It still frustrates me to no end that almost every neuroimaging study you read by default excludes those with IQs less than 80, while our cohort has managed, through very hard work, managed to image individuals with IQs in the 20-60 range with regular success.

I appreciate the effort it takes to include that group. My brother has severe/low functioning autism and he also has very limited language capability (limited vocabulary with simplified grammatical constructions, mix of ASL/SEE signs and spoken words, difficulty producing certain sounds). I've always found it odd that even studies that mainly use data gathered by imaging or other medical tests that don't rely on the subject's mental capacity to participate almost always have no subjects that resemble him at all. I've always assumed it's because it's significantly harder to manage such subjects and probably also very likely for their families to be unable to bring them in for testing in studies that span years.