For the first time, a connection between a specific neurotransmitter pathway in the brain and autistic behavior was discovered

Scientists from Harvard performed a test to discover the differences in behavior between an autistic brain and a normal brain and showed that the differences are related to a break in a certain pathway that uses GABA, one of the main inhibitory neurotransmitters (nerve conductors) in the brain. According to the researchers, the discovery may provide valuable insights for understanding, diagnosing, and perhaps even treating autism, although this is a difficult task.

Scientists from Harvard, led by Prof. Carolyn Robertson, a research associate at Harvard, performed a test to discover the differences in behavior between an autistic brain and a normal brain and showed that the differences are related to a break in a certain pathway that uses the protein GABA, gamma-aminobutyric acid, one of the main inhibitory neurotransmitters (nerve conductors) in the brain. The study was published in the December 17 issue of the journal Current Biology.

"This is the first time it has been discovered in humans that a neurotransmitter in the brain is associated with unambiguous autistic behavior." Robertson said. "The theory - according to which the GABA signaling pathway plays a role in autism was known from animal models, but until now we have never been able to prove that it causes the autistic differences in humans."

Although the discovery may not necessarily lead directly to treatments for autism, Robertson says that the findings provide insight into the syndrome and the role that neurotransmitters such as GABA play in it. Similar visual tests could be used to screen for autism in young children, allowing parents and caregivers to begin early intervention efforts as young as possible.

Although GABA has long been hypothesized to play an important role in autism—GABA has been studied extensively in animal models—evidence supporting GABA's role in the disorder in humans has been elusive.

The sensory input is overwhelming at once

"Autism is often described as a disorder in which all sensory input is overwhelmed at once, so the idea that an inhibitory neurotransmitter is involved is consistent with the clinical observations," Robertson said. "In addition, people with autism often have seizures: there is a co-morbidity of 20-25% between autism and epilepsy -. And we think that the seizures are due to impaired brain stimulation."

To find evidence for this, Robertson and her colleagues looked for a test that could be easily replicated and that would consistently yield different results with and without autism, and they found it in what visual neuroscientists call binocular rivalry. Normally, she said, the brain sees two slightly different images in front of it - one from each eye and from that it creates one image. The rival binoculars test, however, forces each eye to see very different images, with surprising results.

"The end result is that one of the images is completely eliminated from visual awareness for a short period of time," said Robertson. "So if I show you a picture of a horse in one eye and an apple in the other eye the horse will disappear completely and you will only see the apple. Eventually the neurons responsible for inhibiting the signal get tired and the images will alternate until you only see the horse. When the process is repeated, the two images will alternate again and again."

Robertson and her colleagues showed that while the same process occurs in both healthy and autistic brains, the phase of alternating images in an autistic brain takes much longer. "Where the average person jumps between the two images every three seconds, for an autistic person it may take twice as long," she said. "They spend the same amount of time in the steady state - where they only see one image - as the average person, it just takes them longer to switch between them, and the second image is not as suppressed."

Using magnetic resonance spectroscopy, a brain imaging technique capable of measuring the levels of certain neurotransmitters in the brain, the researchers discovered that while in those with autism, normal levels of excitatory neurotransmitters were recorded, the concentration of GABA, which is an inhibitory neurotransmitter, was much lower than expected.
"We believe we have discovered evidence that a lack of GABA in the signaling pathway is the cause of autism. It's not that there is no GABA in the brain, but that at several stages along the pathway it breaks down."

Correcting the course is not an easy thing to do. “GABA is very diverse. There are two forms of GABA receptors, A and B. The GABA A receptor can also come in many forms. We may use a test to test the effectiveness of drugs that will give us clues as to which of these forms are not working properly. But this is something complicated."

"Currently, we cannot diagnose autism in children who do not yet know how to speak, but this is when early intervention will be most effective," she said. "But before the kids can talk they can see, so we might use these kinds of visual tests to scan kids and see if something is out of balance in their brains."

However, Robertson emphasizes that understanding the GABA signaling pathway will not solve all autism problems. "The research is exciting, but there are many more molecules in the brain, and many of them may also play one or another role in autism," she said. "We looked at the GABA story, but we didn't scan the autistic brain for other possible pathways that might play a role. At least we feel good that we understand this route."

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for the scientific article

More of the topic in Hayadan:

• A positive correlation was found between autism and creativity
• Neural connections that may play a role in autism have been discovered
• Relationship between prematurity, late births, and low birth weight and autism in older age