Having strong social ties can cause memory improvement in old age, according to a new study by The Ohio State University researchers.
They determined that mice living in groups developed better memories and had healthier brains than mice living in pairs of two.
“Having lots of friends probably boosts your memory while having fewer makes your memory decline more quickly,” said Elizabeth Kirby, an assistant professor of behavioral neuroscience in the Department of Psychology at Ohio State and lead researcher of the study.
“This relationship between social interaction and memory is probably particularly important in old age because social ties tend to suffer when people retire from the workforce or lose physical mobility.”
Researchers have known for a long time that there is a correlation between memory and social connections in humans, but they didn’t know what caused the connection.
“We don’t know if it’s having a group of friends that’s protecting people or if it’s that people with declining brain health withdraw from their human connections,” Kirby said in a statement.
The researchers set out to find the answer.
The study
To conduct the study, the researchers separated the mice into groups.
Some of the mice lived in pairs, to replicate an “old-couple.” Other mice lived with six other roommates, intended to foster complex interactions.
The mice, ranging from 15 months to 18 months in age, were housed like this for three months.
“It’s like mouse post-retirement age. If they drove, they’d be forgetting where the keys are or where they parked the car more often,” Kirby said in a statement.
In memory tests, the mice living in a large group did better.
The first test required the mice to recognize if a toy had moved to a new location. This is a task that mice with healthy brains should be able to accomplish, said Kirby.
The pair-housed mice were unable to recognize that the toy had moved. The group-housed mice, however, remembered what they had seen before and were able to pick out where the toy had moved to, while ignoring other toys that had not moved.
In the second test, the mice were set on a well-lit round table with many holes. Only some of the holes led to escape routes.
The researchers noted that the natural instinct of mice is to look for dark, unexposed and safe escape routes.
Both groups of mice effectively improved their escape routes with each practice run, but only the group-housed mice were able to get faster when the task was repeated over the course of a day.
The pair-housed mice, over the course of a few days, developed a strategy where they checked every hole very quickly.
“It’d be like walking as quickly as possible through each row of a parking lot to look for your car rather than trying to remember where your car actually is and walk to that spot,” Kirby said in a statement.
The group-housed mice, however, were able to memorize where the escape hatches were, a behavior seen in much younger, healthy mice.
Use of the hippocampus
The memory techniques used by the group-housed mice showed evidence of active use of the hippocampus, a brain region pivotal for memory function.
The pair-housed mice did not demonstrate use of that brain region.
This was backed up by evidence from brain scans.
“When we looked at the brain, we also saw that the mice with many roommates had less signs of inflammation in the hippocampus than the pairs of mice,” said Kirby. “Inflammation in the brain is something that commonly happens with age and seems to be part of what makes the older brain not work so well.”
However, when evaluating neuron growth, the researchers found no difference between the groups.
What initiated the research
Kirby was inspired to conduct this research when her mother moved into a co-housing building with her husband.
The building is made up of a collection of condos, which all hold individuals over 50 years old. They have weekly potlucks and nightly happy hours and do most building maintenance together, said Kirby.
“As I watched my mom in this new community, I thought, all this social interaction, it must be great for her brain compared to just hanging out with her husband in an isolated home,” said Kirby. “I figured I would impress her and find a scientific study showing that boosting your number of social interactions benefits the brain.”
Kirby couldn’t find any studies supporting the evidence she wanted.
“In humans, all I could find were studies showing that more social ties were linked with better brain health,” Kirby explained. “I couldn’t find anything that showed that social ties cause improved brain function in aging.”
“And in rodent studies, the studies that would change the number of social ties animals had would also change other things at the same time, like how many toys they had to play with.”
Kirby was unable to find any study that controlled the amount of social ties that a human or animal had and then tested the effects it had on memory.
“Something as basic as how long it takes to drive or walk to a friend’s house can make a big difference as we get older,” Kirby said in a statement.
“A lot of people end up isolated not by choice, but by circumstance. ‘Over the river and through the woods’ might be fun for the kids, but it’s probably not so great for Grandma,” she continued.
Hypothesis
The study demonstrated factual evidence that isolation is detrimental to memory in older people. It did not, however, give an answer to why this may be.
Kirby has a hypothesis.
“My guess is that living with others is hard,” she said. “It’s work. Coordinating around and with the desires of other people (or other mice) requires a great deal of mental energy. This is basically constant mental exercise. It is also possible that having a strong social network makes you less vulnerable to the negative effects of stress and protects your brain that way.”
