Autism Linked to Brain Neurotransmitter: Study

Many studies regarding autism have suggested an association between brain chemicals and autism spectrum disorder. However, it's only a recent study conducted by Harvard scientists that has successfully made a link between the condition and a specific brain neurotransmitter.

“This is the first time, in humans, that a neurotransmitter in the brain has been linked to autistic behavior — full stop,” study author Caroline Robertson, a junior fellow at the Harvard Society of Fellows, said in a press release.

The researchers used a visual test that elicited different responses in autistic and normal brains. Through the test, found that differences in the brain's responses were associated certain breakdowns in the gamma-aminobutyric acid (GABA) signaling pathways. GABA is one of the brain's neurotransmitters.

“This theory that the GABA signaling pathway plays a role in autism has been shown in animal models, but until now we never had evidence for it actually causing autistic differences in humans,” Robertson said

Although GABA has been long believed to play a role in autism, evidence that could prove the association remain elusive.

In the study, which is published in the journal Current Biology, the researchers attempted to look for evidence that would link GABA to the condition, and used a test called “binocular rivalry.”

According to Robertson, the brain is normally presented with two slightly differing images, one from each eye. On the other hand, this test forces each of a human's two eyes to look at highly different images, eliciting responses.

Robertson explained that what happens is that one image gets suppressed from visual awareness for a short period of time, then as the neurons that suppress the image get tired, vision will switch to the other image. As this process keeps repeating, both images will keep on flashing back and forth.

However, while this “switching” process happens to an average person for around three seconds, it takes a longer time with an autistic person.

Robertson and colleagues have found through this test and a brain imaging technology that although autistic brains exhibited normal levels of excitatory neurotransmitters, GABA was far lower that what was expected.

Although the results seem promising, Robertsons cautioned that understanding the brain's signaling pathways are not a solution, nor a “cure-all” for autism.

“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,” she explained. “We were looking at the GABA story, but we’re not done screening the autistic brain for other possible pathways that may play a role. But this is one, and we feel good about this one.