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How depression impairs memory

Teresa Tanoos's picture
Research shows how depression impairs brain's memory

If you’ve ever suffered from depression, you know how it can slow down thinking and make it difficult to remember if you ever felt happy before.

While researchers have known for some time that depression impairs memory, how this happens has remained unclear. But researchers have recently discovered that it may have to do with the way depression interferes with the ability to differentiate similarities known as “pattern separation” – a mechanism for encoding memories where distinct memories are created for similar experiences.

According to a study published in the journal Behavioural Brain Research, researchers from Brigham Young University confirmed that depression interferes with this ability to separate similar events – and they found that the deeper the depression, the harder is to distinguish between similar events experienced before.

To conduct the study, the researchers administered a computerized memory test to a group of depressed, but un-medicated participants, who had to watch a series of objects on a computer screen and then answer as to whether they had:

1) Seen the object before on the test (old);
2) Seen something like it (similar), or
3) Seen anything like it before (new).

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Although the researchers found that the depressed participants were fully able to distinguish old and new items, when they were shown objects similar to something they had seen before, the most common response was that they had seen the object before.

"We found a negative relationship between depression scores and pattern separation scores. These results provide support for the idea that depression is negatively related to pattern separation performance," wrote the study authors.

They added that this impairment in pattern separation could present memory problems in everyday situations for sufferers of depression, such as remembering certain details like where they parked the car, or to whom they may have disclosed personal information.

"That's really the novel aspect of this study, that we are looking at a very specific aspect of memory. [People with depression] don't have amnesia, they are just missing the details," says Brock Kirwan, a psychology and neuroscience professor at Brigham Young University, who points out that the study also offers clues into what is going on inside the depressed person’s brain.

"There are two areas in your brain where you grow new brain cells. One is the hippocampus, which is involved in memory. It turns out that this growth is decreased in cases of depression," Kirwan explained.

SOURCE: A possible negative influence of depression on the ability to overcome memory interference, Don J. Shelton, C. Brock Kirwan, published in Behavioural Brain Research, Volume 256, 1 November 2013, Pages 20–26 (http://dx.doi.org/10.1016/j.bbr.2013.08.016)