Harvard Researchers Link Neurotransmitter to Autism

Harvard researchers recently linked a symptom of autism with the malfunction of GABA signaling pathways, discovering the first proven connection between autism and a specific neurotransmitter in humans.

Caroline E. Robertson, a Junior Fellow in the Harvard Society of Fellows, led the study, which the journal “Current Biology” published on Dec. 17.

Robertson’s study focuses on GABA, a major inhibitory neurotransmitter that prevents neurons from reacting to sensory information. Based on clinical observations, scientists have for years theorized that people with autism experience dysfunctionality in their inhibitory systems—the part of the human nervous system that slows down or stops the excitation of neurons. In particular, scientists have postulated that GABA plays a role in autism—some animal studies have suggested a relationship—but no human testing established the relationship before Robertson’s paper, according to Bruce R. Kastin, a neurologist at Massachusetts General’s Lurie Center for Autism who was not involved with the study.

The theory suggests that “there’s too much noise in the [autistic] brain, as if you were driving in a car and talking, and it made it difficult for the driver to think about where he was going,” said Kastin.“So the idea was that maybe this was because GABA inhibition wasn’t working correctly. So if you could cool things down or calm things down, it would be easier to think.”

For her study, Robertson’s research team compared results of visual and brain imaging tests on a control group of 21 people without autism against a group of 20 individuals with autism.

The researchers first performed a visual processing test on the subjects, showing them a different image in front of each of their eyes. As the brain processes the different visual information into one image, the researchers “track[ed] the strength with which one of the images is suppressed from visual awareness,” Robertson said.

People with autism had more trouble completing this task, and the rate of such visual suppression is a predictor of the behavioral symptoms of autism, Robertson said.

The research team then tried to link visual symptoms to the GABA system and “close the loop in the GABA hypothesis,” Robertson said.

As the participants underwent the visual tests, the researchers used magnetic resonance spectroscopy, an analytical technique, to measure the concentrations of GABA in the brain.

The results showed that, for the control group, “the more of that inhibitory neurotransmitter [GABA] in the brain, the more they will able to suppress that visual process. But, in the autistic people, that pattern seems altered,” Robertson said.

Robertson emphasized that the results do not indicate that people with autism have lower levels of GABA, but rather that autism may be linked to a “dysfunction in the GABA signaling pathways.".

Although Robertson’s study may not immediately help treat the symptoms of autism, scientists said they hope that the research will heighten understanding of autism.

“I would look at this study as a very exciting first step. Down the line, this type of research could lead to some sort of test or hopefully one day a treatment,” Kastin said.

Robertson said the experiment confirmed clinical observations with empirical evidence. She added that scientists can easily replicate the visual tests in her study, meaning doctors may be able to adapt the tests as a “more objective” diagnostic tool for autism, especially for young children.

—Staff writer Daniel P. Wood can be reached at danielwood@college.harvard.edu. Follow him on Twitter @DanWood145.

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