cnn.com reports:

Your brain consists of two types of tissue, gray matter and white matter. In your first decade of life, the gray matter grows and expands rapidly as many new synapses, or connections between nerves, are being made. The gray matter grows as you learn and are exposed to new experiences as a child.

Then, as your body prepares for puberty, your brain starts to prune back some of that gray matter and amp up its production of white matter, which allows different parts of the brain to share information better and faster, said Dr. Jess Shatkin, a child and adolescent psychiatrist at the Child Study Center at NYU Langone Medical Center….”The brain volume, the total volume, doesn’t really change, but we lose about 1% of gray matter starting around 13 and we gain about 1% of white matter at the same time, and that trade off keeps going,” Shatkin said.

However it seems that in both autism and schizophrenia, this process goes wrong, with autistics ending up with not enough white matter and schizophrenics ending up with not enough gray matter.

Webb MD states:

Researchers say white and gray matter are both necessary for general intelligence, but they perform different functions. Gray matter represents information processing centers in the brain, and white matter represents the network or connections between those processing centers.

The lack of white matter might explain why autistics tend to have narrow interests. If white matter allows different brain parts to share information, which is needed for broad interests, those lacking this may be forced to focus on a single topic.

This may also explain why autistics lack social skills. Reading people requires integrating verbal and non-verbal cues and thus using different parts of the brain at once.

Perhaps this research also reveals why autistics tend to come from high IQ families (or at least higher class ones) or why high people often show a dash of autism. Having a lot of gray matter is linked to high IQ, but if your kid inherits only your gray matter genes without the developmental timing to prune that gray to make room for white matter, he might be severely autitsic.

Meanwhile the high white to gray ratio of schizophrenics may help explain their delusions. Sharing information between unrelated brain parts might lead to a lot of creative theories, but if you lack the gray matter to test these theories with logic, you soon could lose contact with reality.

Research into gray and white matter is further evidence of Crespi and Badcock’s theory that autism is the opposite of schizophrenia.

It also supports Simon Barron Cohen’s extreme male brain theory of autism, in that males tend to have higher gray/white matter ratios than females.