As we reported earlier, a team of researchers led by Caroline Robertson, a junior fellow from the Harvard Society of Fellows, has just released a landmark study linking a commonly studied neurotransmitter with certain symptoms of autism. The study could pave the way toward a new understanding of the condition, as well as open up the door for new treatment and diagnostics methods.

The study focused on GABA, a prominent inhibitory neurotransmitter found in the brain. Researchers long suspected that autistic behavior may have something to do with the chemical balance inside the brain, but this marks the first time that a neurotransmitter has been specifically linked to autism.

Researchers have been able to show the link between GABA and autism in animals, but the recent study provides some of the first evidence that the link holds up in human brains as well. The discovery may not reveal how to treat autism right away, but it provides a critical reference point from which experimental treatments can be tested.

GABA is an inhibitory neurotransmitter, and it blocks out unnecessary stimuli so that the brain can process important information first. Autism is marked by the inability to tune out extraneous sensory information, leaving sufferers feeling overwhelmed. Robertson and her team found that autistic adults were much more likely to have lower levels of GABA in their brains, suggesting that they had trouble tuning out extraneous information.

To test this hypothesis, Robertson showed a group of adults, 50 percent of whom had autism, two slightly different images so that they could be seen one from each eye. Known as the binocular rivalry test, it tests a person’s ability to process two separate images from two different eyes into one coherent image that is perceived by the brain.

Robertson knew that a person with a functional level of GABA in the brain would soon block out one of the mismatched images, eventually perceiving just one object. People that had lower than normal levels of the GABA neurotransmitter would have a harder time deciding which image to focus on.

The results showed that autistic people had much more trouble in the binocular rivalry test than people without autism. Using magnetic resonance spectroscopy, a technique that measures the levels of various neurotransmitters in the brain, Robertson found that GABA levels were much lower in autistic patients than she expected.

The study did not determine where along the GABA pathway autistic people were different from a normal person, and further studies will need to be carried out in order to fine tune methods for diagnosing and treating abnormalities in the brain, but the study represents a great step forward in the scientific understanding of autism.

A press release from Harvard describing the study’s findings can be found here.