Being surrounded by people who don't see the world quite like you do increases your risk of feeling lonely, even if you're friends with them.

Neuroimaging tests on 66 young adults discovered significant contrasts in the way lonely people's brains process information compared to their peers.

The research from the University of California found significant differences existed not just between lonely and non-lonely volunteers, but between individual loners as well.

"It was surprising to find that lonely people were even less similar to each other," says psychologist Elisa Baek.

So what's going on in the brains of people who see themselves as socially isolated? Not feeling understood can be a big part of why some feel disconnected from others, and Baek and colleagues wanted to find out more about this connection.

We're all likely to experience loneliness during our lives, an emotional state when we perceive a gap between our desired and actual relationships. Loneliness often relates more to the quality of our relationships than their quantity, and it impacts our health in multiple ways.

In their study of 66 first-year college students aged 18 to 21, the researchers used functional magnetic resonance imaging (fMRI) to view brain activity while the students watched 14 video clips.

The content was intended to be engaging enough to minimize differences in data arising from participants' minds wandering during the task. The topics in the videos ranged from sentimental music videos to depictions of parties and sporting events.

The participants completed the UCLA Loneliness Scale, a self-report to measure their feelings of loneliness and social isolation, and were divided into two groups based on results: lonely and "nonlonely" (those not experiencing loneliness).

Baek and team analyzed how 214 different regions of the brain responded over time to stimuli in the videos, comparing activity between different individuals in each brain region to see how similar or different their responses were.

While nonlonely people were more or less similar neurologically speaking, individuals with high levels of loneliness, regardless of how many friends they had, were more likely to have unique brain responses.

"Our results suggest that lonely individuals process the world in a way that is dissimilar to their peers and to each other," Baek and colleagues write in their published paper, "which may contribute to the reduced sense of being understood that often accompanies loneliness."

Particularly, differences in neural responses between lonely people and their peers were clear in default-mode network regions, where similar responses have been linked to shared perspectives and subjective understanding. Loneliness was also linked to lower similarities in regions involved in the brain's reward system.

When they accounted for demographic similarity, actual social isolation, and friendships between individuals, these relationships still existed.

It's not clear whether the unique processing in lonely people is a cause or a result of their loneliness, but a lack of shared understanding is certainly likely to impact the relationships people can build.

"The fact that they don't find commonality with lonely or nonlonely people makes achieving social connection even more difficult for them," says Baek.

Being lonely can be awful and not always obvious to those around us. That feeling of being disconnected can totally mess with mental and physical health.

Hopefully further research can figure out how to help lonely people feel more connected and understood.

The research has been published in Psychological Science.