A new autism study reveals that autistic children have many more brain cells than their typically developing peers, with brain heaviness seen while the baby is still in the womb.

Scientists at the University of California, San Diego Autism Center of Excellence studied the brains of 13 boys, seven with autism and six who were developing normally. They found the autistic children had a whopping 67 percent more brain cells than their average counterparts, as well as having brains that were 17.6 percent heavier than normally developed samples.

What do these findings tell us? The roots of autism, which affects one in every 150 children in the U.S., may be in having too many neurons, not too little, and that this dangerous overflow occurs, not during toddlerhood or infancy, but while babies are still developing in the prenatal stages.

Too Much of a Good Thing.

Having so many brain cells sounds like a good thing, until one examines the area where this 67 percent increase occurs. The study focused on the prefrontal cortex, which specializes in social, emotional, communication and language development.

Having too many neurons, or nerve cells, in the prefrontal cortex may be what triggers autistic children's lack of development in just these areas. When the brain has too many neurons, something happens which resembles the tangled pile of wires and extension cords at most people's desks: wiring gets crossed.

In autism, something is going terribly wrong with mechanisms that control the number of neurons, said lead author Eric Courchesne, Ph.D. If there's too much neural wiring in the prefrontal cortex, it might help explain why children with autism exhibit poor social skills and difficulty expressing emotion or communicating.

This is a good example where you have too much of a good thing, it can be bad for you, Dr. Max Wiznitzer, a neurologist and autism expert at the Rainbow Babies and Children's Hospital in Cleveland, Ohio, told CNN Health.

This is not consistent with the claims that heavy metals [from vaccines for example] cause the death of brain cells, says Wiznitzer. Rather than fewer brain cells causing autism, it would appear that the unexpected increase is to blame.

Small But Significant

This autism study is a very small one, and cannot be taken as proof of a pattern in autistic neural development. The study is significant however, for what it suggests, and what other sources were used for the study.

Courchesne's research suggests that contrary to some popular theories of autism, brain problems occur before autistic children are born, rather than during toddlerhood. It also suggests that the bulk of autism's effect on the brain is felt early on, in the prenatal and perinatal stages of development, and not caused by environmental factors in infancy.

How can Courchesne tell? Because only two areas of the brain generate neurons after birth, namely the hippocampus and the olfactory bulb. The hippocampus can affect emotional and social intelligence, but the prefrontal cortex is a powerhouse of prenatal development, growing during the second trimester of pregnancy.

For years, it's been a big puzzle from the standpoint of evidence. Where is the evidence that autism has a prenatal origin? Courchesne told MSNBC. For the first time, we have something really solid.

These findings add to mounting evidence that autism develops before birth in some, possibly all, cases, according to an accompanying editorial to the study.

These new results, along with an earlier study reporting altered wiring of the prefrontal cortex, focus our attention on this critical area of the brain in autism, Dr. Thomas Insel added. Insel is the director of the National Institute of Mental Health, which helps support the UC San Diego program.

The study is also significant purely for the data taken and the youthfulness of its subjects. The study looked at boys between the ages of two and 16. All 13 boys were deceased prior to being studied, a necessary qualifier since counting neurons is impossible while a subject is still alive.

In the past, such restrictions meant that most previous studies looked at older brains, with middle-aged or elderly subjects with severe autism. Given the limited amount of samples available, gathering enough for this study was a remarkable feat.

Brain Heaviness

In addition to finding 67 percent more brain cells in autistic children, Courchesne's study also found the brain of children with autism to be significantly heavier than those of typically developed children. Autistic brains were an average of 17.6 percent heavier compared to control brains weighed in the autism study.

Some children with autism do have overly large heads, a phenomenon charted across the various incarnations of autism spectrum disorder and seen in the study's autistic subjects, who died between 2000 and 2006.

As a baby develops in the womb, the brain typically goes through a period of exponential neural growth, with neuron numbers doubling between 10 and 20 weeks in the womb. This is usually followed however, by half the cells dying away, leaving normal brain sizes and better organized neurons.

Courchesne called the findings dramatic and surprising. He noted however, that he had in fact expected the brain to be heavier. The neuron count indicated autistic brains should weigh around 30 percent more, raising more questions about brain heaviness than it answers.

It's groundbreaking [even though] it doesn't give us a clear answer, says Dr. Jeremy Veenstra-Vanderweele, an autism researcher at the Vanderbilt Kennedy Center.

Still Searching for Cause

Courchesne's study certainly suggests that an excess number of nerve cells, and possibly excess brain weight, is closely linked to autism in prenatal development.

The difference between correlation (a relationship) and causation (cause-and-effect) however, is an important distinction to make, and researchers are still not sure whether autism is triggered by excess neurons or whether these excess neurons, which for unknown reasons begin to multiply, lead to autistic children.

What is certain is that the study is a crucial step forward. [The UC San Diego study] is significant because it narrows the window during development when autism-related brain abnormalities emerge, Dr. Veenstra-Vanderweele said.

This study joins recent, meteoric advances in genetics, neural imaging, neuropathology, animal models and epidemiology. Following the study's publication, more in-depth research, involving many more subjects, is sure to occur.

Autism research, Witnitzer said, is at last turning a corner.