The idea that having a rich social life can help to protect an individual's health is by no means a new one.
Neither is the notion that older people who stay closely in touch with friends preserve better memory and other cognitive abilities for a longer time than their more solitary peers.
The question has always been, "Does sociability protect cognitive abilities, or do those who live with memory impairment tend to shun social activities?"
Researchers from Ohio State University in Columbus have decided to try to clarify this issue. To do so, they worked with a mouse model, but they did not take the same approach as previous studies working with rodents.
In existing research working with mouse models, the investigators gave some of the animals plenty of opportunities to interact with their environment and to explore, while others were given fewer such opportunities.
Instead, study leader Elizabeth Kirby and her colleagues worked with aging mice housed either in groups or as couples, but all of them had equal opportunities to learn and explore.
These strategies, the team explains, allowed them to ascertain which differences in memory recall and learning can be attributed to social connectivity.
"Our research," Kirby explains, "suggests that merely having a larger social network can positively influence the aging brain." The team's results have now been published in the journal Frontiers in Aging Neuroscience.
Sociability tied to better memory
The team worked with mice aged 15–18 months. By then, their brains start to age and cognitive abilities begin to decline. The animals that were housed in pairs were deemed the "old-couple model."
Other mice "lodged" with six more rodents, forcing them to interact more and at more complex levels. All the animals were exposed to these housing conditions for a period of 3 months.
In an expressive analogy, Kirby explains that this situation "[is] like mouse post-retirement age. If they drove, they'd be forgetting where the keys are or where they parked the car more often."
Then, in order to check which mice performed better when it came to learning and memory, the researchers exposed them all to a number of diverse tests.
One test examined the mices' ability to remember small details by placing a toy somewhere in their immediate environment. After a while, the toy would be moved to a slightly different location. And normally, cognitively healthy mice would notice this, and re-explore the object after its relocation.
But, Kirby says, "With the pair-housed mice, they had no idea that the object had moved."
On the other hand, "[t]he group-housed mice were much better at remembering what they'd seen before and went to the toy in a new location, ignoring another toy that had not moved," she explains.
A more active hippocampus
Another test was a maze-type memory exercise, in which the mice are all set down on a round and brightly lit surface with holes. The darker holes signify safe, inconspicuous escape tunnels, and normally, mice would look for those.
After repeated exposure to this situation, cognitively healthy mice would memorize the location of the "escape routes" and waste no time in finding them as needed.
In this instance, the researchers found that both group-housed and pair-housed mice managed to develop better "escape route" searching plans in time, as they went through this test again and again.
However, while group-housed mice, with practice, managed to find the dark holes much quicker — suggesting that they had memorized their location — this was not seen in the pair-housed animals.
The more solitary mice kept searching and searching each time, as though they had not managed to learn the location of the "escape routes" and had to always start their exploration from scratch.
"[O]ver the course of many days, [the pair-housed mice] developed a serial-searching strategy where they checked every hole as quickly as possible," Kirby explains.
"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," she adds.
On the other hand, the behavior exhibited by the group-housed animals was consistent with what healthy, younger mice might do when exposed to a similar situation.
"They seemed to try to memorize where the escape hatches are and walk to them directly, which is the behavior we see in healthy young mice. "
"And that tells us," she says, "that they're using the hippocampus, an area of the brain that is really important for good memory function."
Later life accommodation is important
Kirby and team note that, in humans as well as in mice, memory tends to decline naturally with age. But consistent social interaction seems to protect the brain from this effect.
This was clearly seen when the researchers examined the brains of the pair-housed mice versus those of group-housed mice. In the former, they found evidence of inflammation, which is consistent with neurodegeneration.
On the contrary, "The group-housed mice had fewer signs of this inflammation, meaning that their brains didn't look as 'old' as those that lived in pairs," explains Kirby.
Based on these findings, the research team insist that it is important for people to make informed decisions about where and how they may want to live as they age, as accommodation choices could either facilitate social activities or hinder individuals from maintaining a rich social life.
"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," says Kirby.
However, she also recognizes, "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."