PROVO — You're standing in the parking lot at work, trying to figure out where you put your car. In the back of your mind, there's a niggling notion that you should look at the side lot — or maybe that was where you parked yesterday.
Most people have had that feeling. But a new study by researchers at Brigham Young University indicates that such "pattern separation" is particularly difficult for those who have depression.
The study is published in the journal Behavioral Brain Research.
Pattern separation is the ability to differentiate between things that are similar. Background material provided with the study likened it to children playing the popular Sesame Street game that guides little kids with the prompt, "One of these things is not like the others."
When BYU assistant professor of psychology and neuroscience Brock Kirwan and former graduate student D.J. Shelton, the study's lead author, "played" a version of that game with undergraduates in a psychology class who participated for course credit, they found depression makes it harder to tell whether one has already seen an object or if it is simply similar to something else that was viewed.
New, old or similar?
Using a computer-aided memory test, the students were shown new objects and had no trouble saying they had not seen them before. They could tell which ones they had seen before, too. But when they were shown objects that were similar to but not the same as objects they'd previously seen, students who had some depression didn't do as well sorting it out as those without depression, Kirwan said. And the worse their depression, the worse they did.
"There is correlation between depression rating and performance on the memory task," he said.
The challenge was in noting the details that would distinguish similar from same.
It's not unlike the find-the-car challenge, said Kirwan, who claimed his own version comes when he can't remember which jokes he told in which class.
The researchers tried to control for overall memory performance, taking into account that some people simply remember better than others. It's worth noting, he said, that the group of students overall "weren't very depressed at all. The worst we saw were moderate cases of depression."
Still, it provides insight into a brain process that helps explain the connection between depression and memory. Research documenting likely associations between depression and impaired memory performance go back many years. In 1995, the American Psychological Association's Psychological Bulletin included note of a meta-analysis of multiple studies and concluded that "a significant stable association between depression and memory impairment was revealed. Further analyses indicated, however, that it is likely that depression is linked to particular aspects of memory, the linkage is found in particular subsets of depressed individuals and memory impairment is not unique to depression."
While studies have shown association between depression and lower memory performance, they have not explained how it impacts a memory process. The BYU study does look at a particular memory task. The next step, Kirwan said, will be to take a group diagnosed with depression and see if the finding carries through them.
"Maybe if we know what is going on, what process is affected, we can find a way to treat it," he said, adding that researchers already know the hippocampus is one of two brain areas that grow new brain cells. Earlier research proves when someone has depression, that growth decreases.
The fact that the students were of similar age was not a weakness, but a strength because it eliminated possible confounders, he said, which could call results into question. The biggest deficit was the fact that no one in the group had very severe depression. Still, "we found a pretty robust effect anyway."
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