Autistic Children May Have Too Many Brain
TUESDAY, Nov. 8 (HealthDay News) -- The brains of autistic
children have far more neurons in the prefrontal cortex than the
brains of kids without autism, finds a new study that could advance
research into the disorder.
"For the first time, we have the potential to understand why autism gets started," said study author Eric Courchesne, a professor of neurosciences at the University of California, San Diego School of Medicine and director of the Autism Center of Excellence.
"Creating brains cells and the correct number of brain cells is absolutely fundamental to building the brain," said Courchesne. "If there is an excess number of neurons, there must be a negative consequence to that in the way the brain gets wired or organized."
In this small, preliminary study, the researchers examined
postmortem brain tissue from seven boys with autism and six boys
without autism who were aged 2 to 16 when they died.
The autistic children had on average 67 percent more neurons --
a type of brain cell and a fundamental building block of the
nervous system -- than boys without autism of a similar age.
Specifically, they found autistic children had 79 percent more
neurons in the dorsolateral prefrontal cortex and 29 percent more
in the mesial prefrontal cortex than other kids.
The prefrontal cortex is key to complex thoughts and behaviors,
including language, social behavior and decision-making. The
dorsolateral prefrontal cortex is closely linked with "executive
function," including planning, reasoning and "very high level
cognition," said Lizabeth Romanski, an associate professor of
neurobiology and anatomy at the University of Rochester Medical
Center, who was not involved with the research. The mesial
prefrontal cortex is thought to be important to social and other
behavior and emotions.
While typically developing kids had about 1.16 billion neurons
in the prefrontal cortex, autistic children had about 1.94
The study is published in the Nov. 9 issue of the
Journal of the American Medical Association.
Autism is a neurodevelopment disorder characterized by problems
with social interaction, communication and restricted interests and
behaviors. An estimated one in 110 U.S. children -- many more boys
than girls -- has the disorder, according to the U.S. Centers for
Disease Control and Prevention.
Neurons are generated only during fetal development,
specifically between 10 weeks and 20 weeks, Courchesne said. While
neurons continue to grow in size during childhood, and brain
connections get built and pruned, the number of neurons remains
constant from birth.
That means that whatever goes wrong in autism starts in utero,
which should help focus researchers looking for its causes or
triggers, including specific genes or prenatal exposures.
"Now let's find out what genes or what in-utero, non-genetic conditions lead to an excess number of neurons," he said.
Prior research has also documented "brain overgrowth" in
autistic children, but those studies were done by measuring brain
circumference or MRIs, experts said. In this research, researchers
were able to be more specific by counting brain cells in the
"This very nicely builds on previous research and tries to explain why this increase in brain size might be, and what they find is it's because of an increased number of neurons," Romanski said.
After a period of proliferation during the second trimester,
neurons are also "pruned," meaning that they undergo a planned cell
death. "This pruning process, the dying off of cells, is a very
important part of brain development," Romanski said.
One question that needs to be explored is whether autistic
brains generate more neurons, or if they have a malfunctioning
"pruning" process, she said.
Nicholas Lange, an associate professor of psychiatry and
biostatistics at Harvard Medical School in Boston, cautioned that
the study was small. He also said more needs to be learned,
including whether excess neurons in the prefrontal cortex occur
only in autism or in other developmental conditions, or even in any
typically developing kids, as well.
Some of the kids with autism had many extra neurons, but not all
had brains out of the normal range for weight, as would be
expected. "The relationship between increased neuron count, brain
overgrowth, and increased brain weight in autism is complex," Lange
wrote in accompanying editorial.
Conducting postmortem brain tissue studies is a lengthy process
because there are few brains available to study, Courchesne said.
Eight of the 13 children whose brains were studied had drowned.
"So very seldom do people at that moment make the decision to donate their child's brain tissue for research, and in the absence of brain tissue for research, it goes very slowly," he said.
U.S. National Institute of Neurological Disorders and
Stroke has more on autism.
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