According to John Cacioppo, the director of the Center for Cognitive and Social Neuroscience at the University of Chicago, the reason humans developed such powerful social groups is because the pain of being alone motivates individuals to seek companionship. Researchers at the Massachusetts Institute of Technology think they may have found the source of that motivation in a group of little-studied neurons in part of the brain called the dorsal raphe nucleus, best known for its link to depression. To better understand the role the dorsal raphe neurons play in loneliness, the researchers genetically engineered the dopamine cells to respond to certain wavelengths of light, a technique known as optogenetics. They could then artificially stimulate or silence the cells by exposing them to light. Stimulating the dopamine neurons seemed to make the mice feel bad. Mice actively avoided stimulation if given the choice, just as they might avoid physical pain. Moreover, the animals appeared to enter a state of loneliness — they acted like they had been alone, spending more time with other mice. (May 10, 2016).
