This story's headline reads, "social ties could preserve memory, slow brain aging" and it's illustrated with an image similar to the one shown here. The press release sets out the goal of the study:
“We know that in humans there’s a strong correlation between cognitive health and social connections, but 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,” [Study researcher] Kirby said.
[The n]ew research ...found that mice housed in groups had better memories and healthier brains than animals that lived in pairs.
a) Before reading on, reflect: Why would a researcher probably need an animal model to test this question experimentally?
Here's some more detail about the experiment:
Some mice lived in pairs, which Kirby refers to as the “old-couple model.” Others were housed for three months with six other roommates, a scenario that allows for “pretty complex interactions.”
The mice were 15 months to 18 months old during the experiment – a time of significant natural memory decline in the rodent lifespan.
In tests of memory, the group-housed mice fared better.
One test challenged the mice to recognize that a toy, such as a plastic car, had moved to a new location. ...“With the pair-housed mice, they had no idea that the object had moved. The 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,” Kirby said.
In another common maze-based memory test, mice are placed on a well-lit round table with holes, some of which lead to escape hatches. Their natural tendency is to look for the dark, unexposed and “safe” escape routes.
The “couples” mice didn’t get faster at the test when it was repeated over the course of a day.“But over the course of many days, they developed a serial-searching strategy where they checked every hole as quickly as possible. 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.
The group-housed mice improved with each trial, though. “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,” Kirby said. “And that tells us that they’re using the hippocampus, an area of the brain that is really important for good memory function.”
b) What was the independent variable in this study? How was it operationalized?
c) What was the dependent variable? What were the two ways it was operationalized?
d) How does this experiment help us decide which comes first--social life or better memory? (note: This is temporal precedence!)
e) Do you think the journalist is justified in generalizing this study's results from mice to older adult humans? Why or why not?
f) Chapter 3 explains how internal validity and external validity are often in a trade-off. Describe how this study with mice illustrates that trade-off.