A new imaging study shows that the social part of the brain is both underdeveloped and insufficiently networked in youths with high functioning autism spectrum disorder (ASD) compared to their peers without ASD.
The study, conducted by scientists at the University of California, Los Angeles (UCLA), provides insight into how the brains of children and adolescents with ASD might be organized differently than youths without the disorder.
“The brain controls most of our behavior and changes in how brain areas work and communicate with each other can alter this behavior and lead to impairments associated with mental disorders,” said study first author Dr. Kay Jann, a postdoctoral researcher in the UCLA Department of Neurology.
“When you match physiologic changes in the brain with behavioral impairment, you can start to understand the biological mechanisms of this disorder, which may help improve diagnosis, and, in time, treatment.”
The researchers used imaging technology that tracks both brain blood flow as a measure of energy use and the organization and strength of connections within intrinsic neural networks.
This was the first time an MRI tool known as arterial spin labeling perfusion was used to study ASD. The technique uses magnetically labeled blood water as a tracer to measure brain blood flow. The procedure has been used in other brain disorders, such as schizophrenia, which has already led to novel insights and alternative treatment approaches in that disorder.
“In neurocognitive or neuropsychiatric disorders, these two crucial properties — functional organization of the brain and its accompanying energy demands — are often found to be altered,” said study senior author Dr. Danny J.J. Wang, an associate professor of neurology at UCLA.
The study involved 17 young people with high-functioning ASD and 22 typically developing participants. The groups were matched by age, seven to 17 years old, gender and IQ scores.
The researchers wanted to know whether ASD might be linked to either an increase or a decrease in connectivity within specific neural networks that form the “social brain.” This connectivity can be measured by the amount of blood flow and activity patterns between brain nodes, or neural networks.
“One major brain network, the default mode network, has become a focus of such research, because it is important for social and emotional processes, self-referential thought, and in ‘Theory of Mind,’ which is the ability to attribute mental states to oneself and to others,” Wang said. “These are cognitive processes that are to some extent impaired in persons with autism spectrum disorders.”
The images showed significant differences between the two groups, Wang said. In children with ASD, there was a pattern of widespread increased blood flow, or hyper-perfusion, linked to increased oxygen metabolism in frontal brain areas that are important in navigating social interactions.
This is important because, as a brain develops, blood flow is generally reduced. These signs of continuing hyper-perfusion suggest delayed neurodevelopment in these frontal brain regions associated with socio-emotional cognition, Wang said.
The findings are consistent with previous MRI findings showing an overabundance of neurons in youths with ASD, due to the fact that the synapses of neurons have not been sufficiently “pruned” as the brain develops. Too many functioning synapses inhibit cognition while requiring extra blood flow.
The research team also discovered reduced long-range connectivity between certain network hubs, compared to typical brains. This loss of connectivity means that information cannot flow as it should between distant areas of the brain, which may help explain impairment in social responsiveness, Jann said.
“The architecture of the brain follows a cost efficient wiring pattern that maximizes functionality with minimal energy consumption,” Jann said. “This is not what we found in our ASD participants.”
The findings are published in the journal Brain and Behavior.