Scientists Discover Brain Cells That Regulate Loneliness

For a long time, loneliness has been regarded merely as a psychological or emotional issue. However, neuroscientists are now actively mapping the cellular substrate of loneliness. They have discovered that the desire to congregate with others is actually a fundamental biological need, much like hunger or thirst.

This research was pioneered by Kay Tye, a neuroscientist from the S_alk Institute. Since 2016, Tye has successfully demonstrated that a group of neurons within the brainstem—the deepest and oldest part of the brain—becomes highly active when male mice are isolated for a day and then reunited with their peers.

When scientists inhibited the function of these neurons, the isolated mice became more solitary. Conversely, when these neurons were artificially activated, the mice became extremely enthusiastic about seeking out companions.

In 2019, Tye and her research colleague, Gillian Matthews, proposed the theory that these brainstem neurons are part of a ‘social homeostasis’ system. Much like a room thermostat, the brains of living creatures can detect how much social contact they have received and compare it to an ideal condition or set point.

Further evidence of this ‘social thermostat’ system was found by Catherine Dulac, a neuroscientist from Harvard University and the Howard Hughes Medical Institute. Dulac studied a part of the brain called the hypothalamus, which serves as the control centre for hunger and thirst.

Dulac discovered two groups of neurons that work in opposition: one group becomes active when animals are isolated, and another becomes active when they are reunited. Artificially activating these isolation neurons using optogenetics techniques proved to produce an unpleasant sensation in the mice.

“It is very unpleasant to be alone, in the same way it has been shown that it is unpleasant to be hungry,” said Dulac, who also co-authored a review of social interaction as a fundamental need in the Annual Review of Neuroscience.

Scientists believe that the brain circuits regulating loneliness are similar between humans and rodents, as the deep brain regions controlling this function have nearly identical structures. Much like appetite, this social homeostasis mechanism is spread across various parts of the brain to detect interactions, compare them to an ideal state, and drive our behaviour to either seek out or avoid crowds.

Research indicates that loneliness and weak social connections can increase the risk of dementia by up to 50%. Social interaction is considered vital for maintaining brain health. Studies have found that individuals who frequently feel lonely or isolated during childhood face a risk of dementia up to 31 per cent higher than those who do not.