Though fewer children are diagnosed with autism spectrum disorder (ASD) today than in the past — one in 68 births, up from one in 150 births 10 years ago, according to the Centers for Disease Control and Prevention — many aspects of the disorder are still a mystery. Researchers at Caltech have been studying this mystery and have found neurons that appear to control social behavior in mice. If similar neurons exist in humans, then they may have found the part of the brain that controls autism, leading to more treatment options.
All animals display social behaviors, ranging from very social to completely anti-social. For example, in mice self-grooming is considered anti-social. In humans, social behavior is extremely important, and people who don’t develop normal social behavior, such as autistic people, can have a difficult time living on their own in society. ASD is a developmental disability that is linked to impairments in social interaction and communication, as well as repetitive behavior. In their research paper, published online by the journal Cell on Sept. 11, the scientists suggest that this discovery could also benefit schizophrenic patients.
The researchers tested the mice to discover which part of the medial amygdala is involved in social behavior. They found that a gene called c-fos is elevated in an area of the brain known as the posterior dorsal subdivision of the medial amygdala, abbreviated MeApd, in mice that had recently attacked an intruder. Then they used optogenetics to stimulate the neurons in the MeApd. Optogenetics is the process of using light to manipulate neurons. After activating the neurons in the MeApd, they introduced a more submissive mouse into a cage occupied by a more dominant mouse to see what would happen. They found that activation of the neurons caused the mice to attack the intruders, biting and wrestling with them.
The scientists also discovered the specific type of neurons that produced this behavior: GABAergic neurons, which are neurons that use gamma-Aminobutyric acid as a neurotransmitter. These GABAergic neurons also suppress self-grooming, which is an asocial behavior. However, nearby neurons known as glutamatergic neurons, which use glutamic acid as a neurotransmitter, suppressed social behaviors and caused the mice to start self-grooming when stimulated.
This discovery won’t provide a breakthrough any time soon. Just because the manipulation of these neurons produced behavior that suggests autism in mice doesn’t necessarily mean that they will produce the same changes in humans. However, if the same genes are responsible for human anti-social behavior, then this addition to the way we understand autism is essential. It provides the needed link between brain activity and behavior so that one day we will hopefully have effective treatments for autism spectrum disorders.
Correction: This article previously stated that the rate of diagnosis of ASD was 1 in 50 10 years ago. It was actually 1 in 150.
