Brain images from people experiencing loneliness show distinct features within certain neural regions, suggesting that those who feel lonely may be able to fill their desire for human connection by imagining social contexts and interactions.

Human connection is a key factor in people’s physical and mental health. However, the impacts of COVID-19 and the need for physical distancing are making it challenging to avoid feelings of isolation.

A new study by researchers from the Montreal Neurological Institute-Hospital in Canada, the results of which now appear in the journal Nature Communications, suggests that the brains of people who experience loneliness display specific patterns in a network of regions called the default network.

This network is associated with thinking processes, including the abilities to remember, imagine, and plan for different moments in time.

Participants for this study were around 40,000 individuals from the UK Biobank imaging-genetics cohort, which is an open access biomedical database. The researchers collected initial data for their study through a self-assessment questionnaire on loneliness, along with genetic and lifestyle factors.

The study paper notes that the measure of loneliness was not necessarily dependent on the amount of social contact that each person had. Instead, the team focused on self-perceived loneliness.

In addition to the self-assessment, the researchers also acquired MRI brain scans from the UK Biobank to examine brain characteristics of gray matter, white matter, and functional connectivity.

Gray matter refers to brain regions consisting of neuronal cell bodies involved in processing information, while white matter consists of axons and is involved in transmitting signals. Functional connectivity signifies the communication of signals across brain regions.

Distinctive features of a ‘lonely brain’

For the three examined characteristics, the researchers found that the brains of individuals who felt socially isolated exhibited distinct patterns that were not present in non-isolated individuals. Furthermore, these patterns were central to the area of the default network.

In lonely people, this network contained more gray matter. It also displayed greater stability of the fornix, which is a bundle of white matter in the hippocampus that sends signals to the default network.

Also, the network had stronger connections across brain regions. These patterns indicate that the brain is able to express a unique signature with features that can distinguish a “lonely brain” from a non-lonely one.

The prominence of patterns in the default network is an important finding for understanding the relationships between brain and behavior.

Humans activate this area of the brain when recalling past interactions or daydreaming about future scenarios, which explains how people might seek fulfillment when facing loneliness.

Lead study author Nathan Spreng speculates that loneliness leads to an increased awareness of one’s inner thoughts, which, in turn, stimulates mental processes.

“In the absence of desired social experiences, lonely individuals may be biased toward internally directed thoughts, such as reminiscing or imagining social experiences. We know these cognitive abilities are mediated by the default network brain regions.”

Strengths and limitations of the study

There is limited research into loneliness and the human brain, and even the existing research mainly focuses on brain regions associated with sensory abilities.

This study not only confirms the conclusions of these existing studies, but it also provides new insights into the relationships between loneliness and the brain regions associated with memory and cognition.

Additionally, the study demonstrated the use of robust data by incorporating multiple types of MRI brain imaging and a large sample size.

Out of the participants who self-reported as lonely, 61% were women. However, brain images showed that men exhibited higher levels of patterns associated with loneliness.

Although further research is necessary to understand the reasons for these differences, the study authors note that the discrepancy between these findings and the self-reported data may be a result of the stigma that many men still face.

Next steps in brain research

With the average age of the sample population at 54.9 years, the researchers expect that chronic loneliness into late adulthood will lead to even more distinctions in the brain regions of the default network.

Senior study author Danilo Bzdok says that “expanding our knowledge in this area will help us to better appreciate the urgency of reducing loneliness in today’s society.”

The team plans to further its work by investigating the role of loneliness in the progression of Alzheimer’s disease, which could pave the way for better preventive measures and the development of new treatment options.

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