Researchers have linked reduced action of an inhibitory neurotransmitter, GABA, to behavioral measures in individuals with autism. They are also examining binocular rivalry dynamics in children with autism and the potential of this phenomenon to serve as an early diagnostic marker. While these two key features of autism are well-known, the cause of this brain development disorder remains elusive.
The Harvard team recruited autistic people and a control group and tested their GABA channels, and, sure enough, when tested, the autistic group had a breakdown in how their GABA channels functioned.
The study appears in a December 17 paper in the journal Current Biology.
To find evidence for the theory, Ms. Robertson and colleagues used a visual test known as the binocular rivalry test, for which people with autism consistently have different results to those without the condition. Similarly, this may be a symptom of autism, not a cause; more testing will need to be done, and work on restoring GABA channels is in its infancy at best.
"Autism is often described as a disorder in which all the sensory input comes flooding in at once, so the idea that an inhibitory neurotransmitter was important fit with the clinical observations", Robertson said.
"Our findings show that those afflicted with autism have unstable blood vessels, disrupting proper delivery of blood to the brain", says lead researcher, Efrain Azmitia.
"Individuals with autism are known to have detail-oriented visual perception - exhibiting remarkable attention to small details in the sensory environment and difficulty filtering out or suppressing irrelevant sensory information", Robertson said in a press release.
The 21 autistic subjects underwent trials called "binocular rivalry" - experiments which essentially show different pictures for each eye.
"It's clear that there are changes in brain vascularization in autistic individuals from two to 20 years that are not seen in normally developing individuals past the age of two years", concludes Azmitia. However, an autistic person can take twice as long to "rock" between the two images. "They spend the same amount of time in the steady state - where they see only one image - as the average person, it just takes them longer to switch between them, and the second image is not as deeply suppressed".
In earlier studies, Robertson and colleagues showed that while the same process does occur in the autistic brain, the process of oscillating between images can take significantly longer.
She said: 'It's not that there's no GABA in the brain... it's that there's some step along that pathway that's broken'.
"I'm excited about this study, but there are many other molecules in the brain, and many of them may be associated with autism in some form", Robertson said.
The lead author of a new study connected to this research goes on to explains that the role of GABA is as a signal inhibitor, preventing brain cells from operating as response to external stimuli.
Kallista Images/Getty Images An illustration of the human brain, which Autism Speaks has used as a logo.