In 1995, Baumeister and Leary wrote, “the need to belong is a powerful, fundamental and extremely pervasive motivation” for the social beings we humans are. When we cannot connect with others, when we feel disconnected from other humans, we feel loneliness.

Loneliness affects more than our emotional responses; it can and does affect our physical bodies. In a large meta-analysis that included more than 300,000 individuals, researchers reported that having social connections with others created a 50 percent greater likelihood of survival compared to lonely, disconnected individuals. (Holt-Lunstad, Smith, and Layton, 2010)

Researchers at the University of Michigan conducted a poll comparing reported loneliness in adults between 2018 and 2023. They found that as the COVID pandemic began to necessitate social isolation, rates of loneliness increased, peaking in June 2020 when 56 percent of adults reported feeling lonely. As the pandemic eased and socializing became possible again, rates began to decline to almost pre-pandemic levels. (National Poll on Healthy Aging, 2023)

However, social isolation is not the only cause of loneliness. It is possible to be surrounded by other people, and yet still feel lonely. Because making strong social connections depends on feeling understood by other people, one of the root causes of loneliness is feeling misunderstood by others (Morelli, Torre and Eisenberger, 2014). So, why would people feel misunderstood? Perhaps lonely individuals are seeing the world in a different way than others.

The "Anna Karenina" Principle

To find out, Baek et al. (2014) set out to examine what they called the Anna Karenina principle, an idea inspired by author Leo Tolstoy’s famous opening lines in Anna Karenina about happy and unhappy families. Perhaps people who are not lonely share a common understanding of the world and the people around them while lonely people see the world in their own, individual, idiosyncratic ways, out of sync with others, and leaving them less able to connect with others as well.

Baek et al. separated their volunteer participants into two groups on the basis of their responses to the UCLA Loneliness Scale (Hays and DiMatteo, 1987). Both groups of people watched short, naturalistic videos showing people interacting with one another in a variety of ways, while in an fMRI scanner.

Each video could be interpreted in different ways. The researchers were interested in how the participants interpreted the interactions in the video, their emotional responses to these interactions, and any patterns in how the participants paid attention to the interactions they viewed.

After the fMRI scan was completed, patterns in activation of various brain regions were examined using intersubject correlations (or ISC). Correlations measure the degree to which two sets of measures are related to one another.

Positive correlations happen when both sets of measurements (usually referred to as variable x and variable y) tend to vary together in the same direction: As x increases, so does y. A negative correlation happens when the two variables change in opposite directions—as x increases, y decreases, or vice-versa.

If lonely and non-lonely people are attending to and so interpreting the world in the same way, then brain regions known to be used when we’re attending to important stimuli in the world should show a strong correlation across these two groups. On the other hand, if lonely people attend to the world differently than the non-lonely, the ISC measures should be lower.

Baek and colleagues found that loneliness was associated with lower ISC scores compared to the non-lonely. Specifically, “non-lonely individuals were very similar to each other in their neural responses, whereas lonely individuals were remarkably dissimilar to each other and to their nonlonely peers."

Baek et al found that non-lonely participants' brain regions that showed similar responses were previously identified as important in feelings of being misunderstood, including the dorsomedial prefrontal cortex, precuneus, parietal lobe, and nucleus accumbens.

These regions are often included in the “default-mode network” in the brain, a series of regions that tend to be active together when we’re not actively involved in a specific task or solving a specific problem. These regions have also been associated with understanding and interpreting actions going on around us, and even interpreting basic social relationships like friendship.

Baek et al. concluded that lonely people are processing the world differently than those around them, and this difference may well be part of the feeling of disconnection and difference that is so often a part of feeling lonely.