Depression has long been known to affect memory, but it has been unclear how. Now, researchers say that one reason for this is that depression impairs the process of "pattern separation" - the ability to differentiate things that are similar.
Researchers from Brigham Young University define pattern separation as a mechanism for encoding memories, where distinct memory representations are created for similar objects and events.
But the team's findings, published in the journal Behavioural Brain Research, suggest that depression interferes with this process, and that the more depressed a person feels, the more difficult it is for them to distinguish between similar experiences they have had.
For the study, the researchers conducted a computer-aided memory test on a group of participants who showed symptoms of depression, but who were not receiving medication.
The test required the participants to view a series of objects on a computer screen. For each object, the participants were asked to respond to say whether:
- They had seen the object before on the test (old)
- They had seen something like it (similar), or
- They not seen anything like it before (new).
Results of the study showed that participants with depression were fully able to distinguish old and new items.
However, when they were shown objects that were similar to something they had seen previously, the most common answer the participants gave was that they had seen the object before.
The researchers say:
"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."
The study authors note that this impairment in pattern separation may present challenges for depressed individuals in everyday situations, from remembering where they parked the car, to recalling which friends and family members they have disclosed personal information to.
"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.
Prof. Kirwan notes that the study also provides clues as to what is happening in the brain of those who suffer depression:
"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."
Medical News Today recently reported that people suffering from depression may have an increased risk for Parkinson's disease.