Matthews’ achievement took his career in a new direction. Leaving aside her research on drug addiction, she went to the Massachusetts Institute of Technology in 2013 to join Kay Tye’s lab. Tye is a neuroscientist focused on understanding the neural basis of emotion, and she is also a pioneer of optogenetics – a technique that uses genetically engineered proteins inserted into brain cells to give researchers the ability turn neurons on and off by shining light through fiber-optic cables in the brains of living animals. The approach allows scientists to activate regions of the brain in real time and observe how animals react. “By the time I joined the lab, optogenetics was really exploding, and that opened up so much more potential for the studies you could do,” Matthews says.
Armed with this new technique, Matthews and Tye wanted to understand how DRN neurons influenced mice during social isolation. When the researchers stimulated neurons, the animals were more likely to look for other mice. When they suppressed the same neurons, even isolated animals lost the desire for social interaction. It was as if Matthews and Tye had located the neural switch that controlled the animals’ desire for social interaction – it would turn on when they were isolated and turn off again when their social urges were satisfied.
Their discovery could radically change our understanding of loneliness. “Taking this idea suggests that there are mechanisms in place to help maintain social contact in the same way that there are mechanisms in place to make sure we maintain our food intake or water intake,” says Matthews. This suggests that social contact isn’t just nice to have – it’s a basic need that our brains are wired to seek out. This is already confirmed in bee studies, ants, mice and rats. “Without the full level of social contact, survival declines in many species,” Matthews says.
In 2020, another neuroscientist from MIT published an article suggesting that the human brain responds to social isolation in a manner similar to Matthews’ mice. Livia Tomova recruited 40 volunteers and asked them to return their smartphones, tablets and laptops and spend 10 hours alone in a room. Volunteers could take care of puzzle books and writing materials, but they did not have access to fiction that might contain a hint of social contact that might ease their isolation. If volunteers had to use the bathroom, they had to wear earplugs that prevented them from hearing conversations along the way. “We tried to create a scenario where people really wouldn’t have any input,” says Tomova, who is now at Cambridge University.
Optogenetics are too invasive to be used on humans, but instead Tomova took fMRI scans of the brains of her volunteers. When isolated volunteers were shown photos of social cues, regions of their brains associated with cravings would light up with activity in the same way that hungry people’s brains light up when they were. showed pictures of food. The area of the brain Tomova focused on is rich in dopaminergic neurons, which drive our motivations and expectations of the world around us. When our brain anticipates a rewarding activity – like eating or social contact – these neurons activate in anticipation. But if we don’t get these interactions, then our brain experiences a negative feeling, similar to an urge.
Tomova says this could explain the negative consequences of long-term isolation. “If you are in a state of prolonged stress, the same adaptations that are healthy and necessary in the first place will actually become harmful because they are not designed to be long-term states,” she says. “The idea of cravings is that the goal should be to seek out others and reestablish social contact.”