Researchers found that GABA neurotransmitter malfunctions in the brain in people with autism, leaving them unable to suppress sensory input.
For the first time, scientists have made a connection in humans between autistic behavior symptoms and a neurotransmitter in the brain. According to the breakthrough study’s lead author, Caroline Robertson of MIT’s McGovern Institute for Brain Research, a neurotransmitter known as GABA is responsible for curbing “runaway excitation” in the brain.
In other words, GABA inhibits brain cells from firing in response to signals received from outside. Scientists now think that a lack of the neurotransmitter may cause overexcited neurons to be hypersensitive to sensory input, which is seen in people with autism.
People with autism find it difficult to tune out distracting sights, sounds and sensations, making them feel overwhelmed as sensory input comes flooding in all at once. Robertson says that GABA helps to filter out signals from the external world that are not relevant at the time.
The connection between reduced GABA activity and autism-like behavior had previously been found in animals, but the hypothesis has only recently been tested on humans. In the study, adults were asked to switch back and forth between images, a task requiring brain inhibition. Those with autism were significantly less able to focus on one image while suppressing the other, switching back and forth only half as much as the group without autism.
Researchers from Harvard and MIT measured GABA activity in the participants’ brains while they completed the assigned task, and found that those without autism were better able to suppress one image if they had higher GABA levels. In the autistic group, the GABA levels had no relationship to the ability. Robertson says it is not as simple as saying that particular neurotransmitter is missing in the autistic brain, but rather that it is not doing its job. Researchers are not sure of the cause for the dysfunction, and say a lot more work will be necessary.
The breakthrough does not mean that autism symptoms could be improved by simply increasing GABA, but the findings are promising. Physicians may soon be able to use GABA activity as an early screening mechanism for autism, and may also open the possibilities of treatment and perhaps even prevention of the condition. Robertson cautions that it will not be as simple as curing autism with GABA-enhancing drugs.