The corpus callosum is the largest connection in the human brain, linking the left and right brain hemispheres via about 200 million fibers. In very rare cases it is surgically cut to treat epilepsy-causing “split-brain” syndrome.
People with a condition called agenesis of the corpus callosum (AgCC) are like split-brain patients in that they are missing their corpus callosum—except they are born this way.
In spite of this significant brain malformation, many of these individuals are relatively high-functioning, with jobs and families, but they tend to have difficulty interacting with other people, among other symptoms such as memory deficits and developmental delays.
These difficulties in social behavior bear a strong resemblance to those experienced by high-functioning people with autism spectrum disorder.
“We and others had noted this resemblance between AgCC and autism before,” says Lynn Paul, lead author of the study and a lecturer in psychology at California Institute of Technology (Caltech). But no one had directly compared the two groups of patients.
“When we made detailed comparisons, we found that about a third of people with AgCC would meet diagnostic criteria for an autism spectrum disorder in terms of their current symptoms,” Paul says.
Research for the study, published in the journal Brain, was conducted in the laboratory of coauthor Ralph Adolphs, professor of psychology and neuroscience and professor of biology.
The team looked at a range of different tasks performed by both sets of patients. Some of the exercises that involved certain social behaviors were videotaped and analyzed by the researchers to assess for autism. The team also gave the individuals questionnaires to fill out that measured factors like intelligence and social functioning.
“Comparing different clinical groups on exactly the same tasks within the same lab is very rare, and it took us about a decade to accrue all of the data,” Adolphs notes.
Growth spurt in the brain
One important difference between the two sets of patients did emerge in the comparison. People with autism spectrum disorder showed autism-like behaviors in infancy and early childhood, but the same type of behaviors did not seem to emerge in individuals with AgCC until later in childhood or the teen years.
“Around ages 9 through 12, a normally formed corpus callosum goes through a developmental ‘growth spurt’ which contributes to rapid advances in social skills and abstract thinking during those years,” Paul says. “Because they don’t have a corpus callosum, teens with AgCC become more socially awkward at the age when social skills are most important.”
AgCC can now be diagnosed before a baby is born, using high-resolution ultrasound imaging during pregnancy, opening the door for future research, Adolphs says.
“If we can identify people with AgCC already before birth, we should be in a much better position to provide interventions like social skills training before problems arise,” Paul says.
Annual brain imaging
“And of course from a research perspective it would be tremendously valuable to begin studying such individuals early in life, since we still know so little both about autism and about AgCC.”
For example, the team would like to discern at what age subtle difficulties first appear in people with AgCC and at what point they start looking similar to autism, as well as what happens in the brain during these changes.
“If we could follow a baby with AgCC as it grows up, and visualize its brain with MRI each year, we would gain such a wealth of knowledge,” Adolphs says.
Daniel Kennedy, assistant professor of psychology at Indiana University, and Christina Corsello, a member of the research staff at Rady Children’s Hospital–San Diego, are coauthors on the paper. The Simons Foundation, Autism Speaks, and the Brain and Behavior Research Foundation funded the research.