The study, published Thursday in the journal Frontiers in Aging Neuroscience, found mice housed in groups had better memory and healthier brains than those living in pairs. The findings influence “a body of research in humans and animals that supports the role of social connections in preserving the mind and improving quality of life,” according to Elizabeth Kirby, assistant professor of behavioral neuroscience at The Ohio State University Wexner Medical Center and lead author of the study.
The study used mice that were 15 months to 18 months old during the experiment – a time of significant memory decay. Some of the mice lived in pairs, while others were housed in groups of seven for three months. The first test required the mice to recognize that a toy, such as a plastic car, had been moved to a new location.
A mouse with a healthy brain would recognize something has been relocated, and mice that lived in larger groups generally fared better on this assessment, according to Kirby. “We found that mice housed in groups remembered objects better,” Kirby says.
In another maze-based memory test, mice were placed on a table with holes, and both groups of mice were tasked with finding new escape routes every time. With four total trials a day, it was noted that both groups improved their escape routes each time. However, the coupled mice did not complete the test faster when it was repeated several times. But the group-housed mice improved performance with each trial, suggesting they used their hippocampus, an area of the brain associated with memory.
“One of the holes had an escape hatch,” Kirby says. “Every day we’d place the hatch in a new location. We found that all mice [found the hatch] quickly, but the difference was in how they did it.”
Paired mice performed what is known as a “serial search,” checking the holes for the hatch systematically, Kirby says. While the method is efficient, it is easier to do and less effective than “spatial searching,” which is what the group-housed mice did to find the hatch. Spatial searching involves remembering where the hatch was the first time and trying to find it in subsequent trials.
“A parallel in humans is trying to remember where you parked your car,” Kirby says. “If you have some memory of where it is, it’s much more efficient to navigate directly to your car.”
In healthy humans, mice and other animals, brain function in the hippocampus declines with age. Social ties are recommended to preserve memory in this region of the brain in humans, Kirby says. Although there were no differences in neuron growth in the hippocampus between the two groups, researchers found increased inflammation in the brain tissue of coupled mice, which is evidence of declined cognitive health.
Joseph B. Orange, a professor of communication sciences and disorders at Western University in Ontario, Canada, says this research is helpful for identifying the impact of social connections on brain health.
“This advances our research that identifies social inclusion versus exclusion in advancing people’s lives,” says Orange, who was not involved in the research. “We want to use models that help our research in humans. Mice and humans share a lot in DNA structure, so the models used here are quite applicable.”
People who are isolated with limited social contact tend to have higher levels of depression, a higher use of medications for treating psychosis and more overall hospitalizations, according to Orange, which means the results of this study, though helpful, are not surprising.
“This research adds a small tile in the larger mosaic of social exclusion and how it affects cognitive skills, communication performance and overall quality of life,” Orange says.
Future research should explore the connection between social groups, longevity of life and brain health, Kirby says. People who are aging should consider how their living situation might influence their social circles, Kirby concludes.
“Think about your living situation as you age,” Kirby says. “If you have the privilege of choosing where you live, make the choice so you can be socially engaged as long as possible.”
