From that craving for a reassuring hug, a helping hand when you need it most, or someone to talk to after a long day — we all likely know how painful pangs of loneliness can feel.
“Throughout human history, we’ve had to rely on others for our survival, whether that’s protection from physical threats or our need for a sense of community,” explains Julianne Holt-Lunstad, PhD, a professor of psychology and neuroscience at Brigham Young University in Provo, Utah. “From a neuroscience perspective, our brains have adapted to social proximity.”
In other words: We’ve adapted to feel safer and more secure when we feel like we’re not alone.
According to the American Psychological Association (APA)'s definition, loneliness is the discomfort or uneasiness of being or perceiving oneself to be alone — the emotional distress we feel when our innate need for intimacy and companionship goes unmet.
And while passing, transient loneliness is a feeling we’ll all likely encounter at some point or another, when loneliness is chronic or severe, the long-term effects can be very detrimental to health.
“When we’re lonely, our brains are in constant alert. We’re in a state of feeling physically threatened, and that interferes with our thinking and perception,” Dr. Holt-Lunstad says.
Here are four big ways loneliness can lead to changes in the brain that affect our thinking, perception, and well-being.
1.Loneliness Can Cause ‘Cravings’ for Companionship as Strong as Hunger or Thirst
Research suggests that loneliness triggers neural responses in the brain similar to the activity they see when people are hungry and want food.
In a study published in Nature Neuroscience in January 2021, neuroscientists had 40 healthy participants stay isolated for 10 hours, followed by 10 hours of fasting. After each 10-hour block, the neuroscientists used functional magnetic resonance imaging (fMRI) to measure brain activity, and compared it with the participants’ baseline fMRI scans.
“A hungry person looking at food and an isolated person feeling loneliness cues — they shared the same neural signature between those two states,” says the lead author,Livia Tomova, PhD, a neuroscientist at the University of Cambridge in England, where she specializes in studying how stress, loneliness, and social isolation affect the brain and mind.
Other studies have suggested that when we feel lonely and rejected, brain regions tied to feelings of uncertainty, ruminating, and stress light up. The researchers behind one review on the topic hypothesized that these cues alert us to return to social connection.
“Loneliness is not just an adverse state, it’s a signal that something is lacking, and that we need to take action,” Dr. Tomova says.
2. Loneliness May Make Us More Hostile and Pessimistic
Feeling lonely may make us more likely to focus on the negative in a situation. Researchers have found this to be true in experiments that used fMRI scans to show that the brain indeed activates more in response to negative stimuli than positive triggers, according to previous review on the topic.
It’s a “self-preservation” response, wrote two coauthors of that study, Stephanie Cacioppo, PhD, an assistant professor of psychiatry and behavioral neuroscience and the director of the Brain Dynamics Laboratory at University of Chicago, and her late husband, John Cacioppo, PhD, who studied social neuroscience for decades.
Because lonely people often don’t have anyone looking out for them, they end up being hypervigilant to potential threats. This kind of thinking turns into a vicious cycle, according to a study published in the journal Psychology and Aging in March 2020.
In the sample of 7,500 older adults who answered survey questions, that data revealed that lonelier people tended to be more likely to feel hurt or hard done by loved ones, withdraw from their relationships, and even act with “cynical hostility.” While the researchers suggest that hostility is a defense mechanism lonely people employ because they fear further rejection, it still results in pushing people (and the companionship they crave) further away.
In a study published in the journal Psychiatry in 2017, researchers called this a “self-reinforcing loop” of participants feeling lonely, criticizing their friendships, and isolating themselves from others.
3. Feeling Lonely May Make Us Less Likely to Trust Others
Lonely people are more alert to potential threats around them, and that may lead to higher levels of distrust in others. For astudy published in the November 2021Advanced Science, researchers recruited 42 people with severe, persistent loneliness who weren’t diagnosed with serious mental health conditions and a control group of the same size.
For one task, participants were given imaginary money and were asked whether they wanted to keep it all or share with other participants. If they shared their cash, the monetary value would triple and the person they shared it with could return some of the funds; participants could earn more cash in the experiment, but only if they took a chance on trusting the other players.
The lonely participants shared less with others than their non-lonely counterparts. And fMRI scans showed lonely participants had less activity in parts of the brain associated with trust formation, too. (Previous research found that this part of the brain — the amygdala, or emotion processing center — is smaller in people with smaller social networks.)
Furthermore, blood and saliva samples that measured levels of oxytocin (a hormone that, among other functions, plays a role in bonding and attachment to others) revealed that non-lonely participants’ mood increased during small talk, while lonely participants’ didn’t. Lonely participants were more likely to report not trusting the research assistants, and produced less oxytocin than the control group.
“This is one of the more worrisome signs of loneliness — when you’re paranoid that people you don’t even know are out to give you a hard time. It’s a sign you’ve spent too much time alone,” says Jacqueline Olds, MD, a psychiatry consultant at Massachusetts General Hospital and the author of Overcoming Loneliness in Everyday Life.
4.Loneliness May Contribute to Cognitive Decline
We also need to socialize to keep our brains stimulated, says Tomova.
“Social interaction in and of itself is a primary reward for social animals. It activates reward centers in our brains; it’s an interaction that isn’t meant to fulfill other goals — it’s truly just an enjoyable act,” she says.
Research has pointed to changes in the brain when people grapple with above-average levels of loneliness. A letter to the editorpublished in the New England Journal of Medicine in 2019 described a study that followed the health trajectories of nine polar expeditioners who lived in solitude in Antarctica for 14 months. The researchers found that a part of the crew members’ brains — the dentate gyrus — shrank by about 7 percent. The dentate gyrus is responsible for feeding information into the hippocampus to help with learning and memory.
The crew members even had reduced blood levels of a protein called BDNF — or brain-derived neurotrophic factor — which plays a role in stress regulation and memory; decreases in BDNF were significantly linked to decreases in dentate gyrus volume. Overall, the polar explorers fared worse on memory and spatial processing tests.
People don’t need to be isolated in the Antarctic to experience this effect. In a study of more than 11,000 people published in 2019 in the Journals of Gerontology, scientists found that those who reported high levels of social isolation had above-average decline in cognitive function when it came to tests of memory recall.
