|Depression may cause an inability to see differences|
Depression has been linked to memory impairment, but it doesn't affect all types of memory the same way. A new study suggests that people with depression can remember the big picture, but have difficulty recalling fine details.
Brigham Young University professor Brock Kirwan and one of his former grad students, D.J. Shelton, set up a memory test where participants were asked to look at various objects that popped up on a computer screen, and mark them as a new object (something they hadn't seen in the test already) or an old object (that they had seen). Out of 83 participants, those who were more depressed (assessed by pre-study surveys) could usually tell the difference between objects they had or hadn't seen before, but were significantly more likely to categorize objects that looked similar, but not exactly the same, as "old."
“They don’t have amnesia,” according to Kirwan. “They are just missing the details.”
Difficulty distinguishing between details could be because depressed people have smaller hippocampi--the hippocampus being a vital brain region for memory processing. Some of Kirwan's previous work has connected the hippocampus to pattern separation abilities. During depression, the researchers hypothesize that the brain seems to stop producing new neurons in the hippocampus, in turn affecting pattern separation abilities.
Because the study didn't use people with a clinical diagnosis of depression, and the average level of depression in their participant pool was fairly mild, it's hard to establish direct causation between depression, neurogenesis and pattern separation abilities. (The researchers ruled out 15 participants from their dataset for antidepressant use, since it has been suggested to increase neurogenesis, the creation of neurons.) Future studies will be needed.
The study is in the November 1 issue of Behavioral Brain Research