{shortcode-550eb1ada90d671aca4840057cebc4c9637f5b05}

Researchers in the Molecular and Cellular Biology Department published a study last week that found a brain drive for social interactions in mice, similar in neural organization to drives for hunger and thirst.

“Social stimuli are the most salient, the most important stimuli for animals and humans,” said Harvard MCB Professor Catherine Dulac, who led the study.

“If I’m hungry, I feel it very clearly — or if I’m thirsty or if I’m sleepy. If I need social interaction, it’s not as explicit,” Dulac said. “So this really points to an important need that maybe people either ignore or don’t view as important.”

The study, published in the scientific journal Nature, identified specialized separate groups of neurons activated in mouse brains during times of social isolation and reunion.

“Social behavior is really like other fundamental needs and is essential for health, and regulated in a similar brain or neuronal structure,” said Ding Liu, a postdoctoral fellow at the Dulac Lab who worked closely on the project.

In an experimental design that isolated individual mice to track their behaviors and assess neuron activity, the study’s researchers observed patterns in brain activity and behavior that correlated with social reunions. The mice perceived social isolation as aversive — experiencing a “negative valence” — but reunion with other mice after isolation generated a rewarding experience.

“There’s something fundamentally essential about social interaction, and I think this is particularly clear when both animals and humans are put in isolation,” Dulac said. “They just don’t function very well.”

Dulac added that an “extremely intense interaction” — known as a “rebound” — occurs when formerly isolated animals are brought back together, at a level of intensity proportional to the length of isolation.

Dulac classified this rebound as a property of “homeostatic needs,” drawing a comparison to the increase in sleep that a student might experience the night after an all-nighter.

“I don’t think people so far have understood the need to be together as a survival need,” Dulac said, adding that she hopes the study imparts the “importance of social interaction for wellbeing.”

Pointing to the study’s discovery that the “architecture” of the neural circuitry driving social behavior is “the same as the one driving sleep, hunger, or thirst,” Dulac raised questions about the morality of solitary confinement in prisons.

“If you think about prisoners that are put in social isolation — for example, solitary confinement,” Dulac said, “You would not be authorized to deprive somebody of food or sleep or water.”

“So maybe what we find suggests that you also could not — you should not — deprive somebody of social interaction,” Dulac added, calling solitary confinement “a discussion that people should have.”

Another finding in the study was that the mice displayed a need for physical touch. In the study, researchers observed a preference in the mice for a soft cloth environment as opposed to a hard, plastic one, indicating the importance of touch as a way for mice to “perceive social environment.”

While more research needs to be done to confirm a similar neural system of dependence on social interaction in humans, Liu remains optimistic.

“The reason humans, homo sapiens, can stand out from other species is because we can collaborate in a really large scale, right?” Liu said, pointing to landmark collaborative human projects like constructing pyramids or landing on the moon.

Liu added that social drive is “a main theme for the meaning of life.”

Dulac stressed that animals highly prioritize social interaction — even in comparison with more conventionally rewarding pleasures.

“If you give a choice to a rat between cocaine and meeting another rat, they will choose another rat,” Dulac said.