This increased quantity of nerve cells must result from something that occurred prenatally, like an infection or genetic abnormality
A small study looking at the brains of children with autistic spectrum disorder who have died has shown that the autistic children have more neurons in a certain region of the brain than their normally-developing peers. This region, called the prefrontal cortex, is known to be involved in social, emotional, and thinking skills.
Since the number of cortical neurons is determined before birth, this increased quantity of nerve cells, the researchers maintain that it must have resulted from something that occurred prenatally. An infection, a toxic exposure, a genetic abnormality, a dysregulation of cell growth, or other mechanism may be the agent responsible.
In a painstaking process, the researchers studied the brains of seven autistic children and six non-autistic children who had died. They measured the weights of the brains, examined the brain tissue, and counted the neurons in the brain regions of interest. The diagnosis of autism in the deceased children was established by a rigorous questionnaire administered to a parent or guardian of the child.