What Loneliness Looks Like in the Brain
By Veronica Diveica
Humans have a deep need for social connection. That’s not surprising — our ancestors depended on one another for survival, cooperating to find food, keep each other safe, and raise children. Throughout evolution, sociality became embedded deep in our biology. Today, our social relationships remain essential not just for survival, but for our sense of fulfillment and happiness.
When our social needs aren’t met, we feel lonely. Loneliness isn’t simply about how much time we spend alone or how many friends we have. It’s the feeling that our social connections — in either quantity or quality — fall short of what we want. About one in six people experience loneliness, which is worrying because loneliness can harm both mental and physical health. Research suggests that chronic loneliness increases health risks as much as obesity or smoking 15 cigarettes a day. Because of its serious consequences, the World Health Organization now recognizes loneliness as a major public health issue.
To better understand loneliness, a team of researchers led by Professor Nathan Spreng (2020) examined how it manifests in the brain. Their study drew on data from the UK Biobank, which enabled the researchers to study brain scans and health information from a staggering 40,000 adults in the UK. They compared people who reported feeling lonely often with those who did not, using three different types of brain measures — each offering a unique perspective on how loneliness manifests in the brain.
1. Gray matter volume:
Gray matter contains the cell bodies that process information. Lonely individuals showed differences in gray matter volume across many brain regions — most notably within the “default network”. Regions comprising the default network work together to support many complex abilities like self-reflection, remembering the past, imagining the future or “what might have been”, and understanding others’ identities, intentions, thoughts, and social affiliations.
2. Functional connectivity:
Functional connectivity reflects the tendency of brain regions to activate together, revealing how different parts of the brain coordinate their activity. Using fMRI scans collected while participants rested quietly in the scanner, the researchers examined these patterns of functional connectivity. Lonely individuals showed stronger functional connectivity within the default network and between the default network and other regions involved in vision, attention, and emotion.
3. White matter integrity:
White matter tracts are the brain’s communication highways. Lonely participants had stronger integrity of a white matter pathway called the fornix, which connects the hippocampus, a default network region crucial for memory, with the limbic system involved in emotion.
The analyses of the three brain measurements all point to a connection between loneliness and the brain’s default network. Interestingly, loneliness was linked to stronger — rather than weaker — functional connectivity of default network regions and integrity of the affiliated fornix pathway. This raises the possibility that these brain differences reflect a more internally focused mental state in loneliness: in the absence of social interactions lonely individuals may spend more time reflecting on past experiences, imagining possible future events, or mentally simulating social interactions. Indeed, loneliness has been associated with more frequent nostalgic reminiscing, daydreaming about other people, and treating pets as if they were human companions .
It’s still unclear whether these brain differences cause loneliness or result from it. Either way, they show that loneliness is not just a social or emotional experience — it’s reflected in the brain’s structure and function.