In a new study in the August issue of Nature, scientists at the NYU Langone Medical Center discovered how the brain filters useful information. The team, led by Dr. Richard Tsien, zeroed in on oxytocin neurons in the hippocampus of rats.
The hippocampus is the part of the brain used to form new memories. An earlier study found that the chemical oxytocin acts on the hippocampus. Oxytocin functions as both a hormone and a neurotransmitter in the body, playing a vital role in childbirth and emotional bonding. In autistic people, who sometimes struggle with empathy, scientists have found that oxytocin levels are lower than usual.
In order to form memories, the hippocampus relies on brain cells called pyramidal neurons and interneurons. These interneurons act as a filter, so that small distractions in the environment don’t send a strong enough signal for a memory to form. When a powerful signal from a real stimulus comes through, it’s enough to overcome the inhibitory interneurons and make the pyramidal neurons fire. This allows important stimuli to active the hippocampus, but ignores irrelevant details.
Tsien’s team found that when oxytocin levels are high, interneurons are not able to transmit as strong a signal. The balance of power between interneurons and pyramidal neurons allows the brain to carefully fine-tune which information it retains and which it doesn't. Unfortunately, such a delicate system is easily disrupted.
Seeing the World Through Autistic Eyes
Tsien’s findings may shed light on why autism causes differences in the processing of social and environmental cues.
Autistics tend to focus more on visual and spatial details, while ignoring the “big picture,” called a gestalt. For example, in the image above, when asked what letter they see, an autistic person is more likely to spot the 'A’s' and have trouble seeing the 'W' that they form together. However, they’ll also identify the A’s faster than a non-autistic person would.
This becomes problematic in social situations, such as listening to one person talk in a crowded room or trying to read a person’s emotions from their facial expressions and tone of voice.
"Most of us will be able to look at a face and very quickly extract a person's expression and have an understanding of what the person’s underlying emotional state is,” explains Dr. Alexander Kolevzon, Clinical Director at the Seaver Autism Center in the Icahn School of Medicine at Mount Sinai. “We can rely on a gestalt, a pattern we can recognize. In people with autism, this gestalt is absent. It's not intuitive to them where they should be focusing their attention. They have to analyze the face in a piecemeal way. There's a nose, an eye...oh, it's a face. Trying to understand the expression beyond that is even more difficult."
Can Oxytocin Treat Autism?
Several studies have investigated the oxytocin-autism connection. A single dose of oxytocin has been found to help autistic people with empathy and other social tasks. One study, published last year, found a lasting effect from the chronic use of oxytocin.
Tsien’s finding might help explain why. Autism is linked to both lower oxytocin levels and mutations in the oxytocin receptor, the site where oxytocin bonds to its interneuron and causes it to fire. If the neurons responsible for filtering out unnecessarily information and highlighting important information aren’t receiving the oxytocin they need, they won’t be able to function as efficiently.
Although many autistic people learn to compensate by using their intellect to develop rules and algorithms to follow, this requires incredible effort.
"I think what happens for people with autism is that when they're walking around, the environment can be quite overwhelming for them,” Kolevzon explains. “What they're most likely to miss are those social cues. One of the reasons they avoid social contact is because it can be exhausting. All those things don't come naturally to them."
Kolevzon is one of the lead researchers in a new study funded by the NIH to test oxytocin as an autism treatment. They will be recruiting subjects ages three to 17 starting this fall at five locations: the University of North Carolina, the University of Washington, Vanderbilt University, Harvard University, and the Icahn School of Medicine at Mount Sinai.
For more information about this study or other ongoing work at the Seaver Autism Center, please contact Sarah Soffes at (212) 241-2993.