The more depressed someone feels, the harder it is for them to distinguish similar experiences they've had.
Depression has been generally linked to poor memory for a long time. To find out why, Brock Kirwan, a psychology and neuroscience professor at Brigham Young University and his former grad student D.J. Shelton put people through a computer-aided memory test.
The participants viewed a series of objects on the screen. For each one, they responded whether they had seen the object before on the test (old), seen something like it (similar), or not seen anything like it (new).
With old and new items, participants with depression did just fine. They often got it wrong, however, when looking at objects that were similar to something they had seen previously. The most common incorrect answer was that they had seen the object before.
Kirwan said that there are two areas in your brain where you grow new brain cells.
He said that one is the hippocampus, which is involved in memory. It turns out that this growth is decreased in cases of depression.
The study has been published in the journal Behavioral Brain Research.