This study focuses on exploring the impact of depressive symptoms on memory experienced by 2,500 adults with depression or a depressive history. They were tested on a range of memory measures. Prior to the study, the researchers found that the ability to remember relevant information over time is reduced in people who experience depression possibly due to over-exposure to increased levels of corticosteroids (from high psychological stress from a depressive episode). Studies prior to this one also support that there is a shrinkage in volume of the hippocampus in people with depression. The researchers of this study predicted that symptoms of depression experienced in the general population would be related to memory problems and that would be related to a decreased size of hippocampus. Other research suggested that subjective memory (one’s own perception of their memory abilities) complaints are heightened in people with depression because they think their depression is making things worse. The researchers in this study predicted that subjective memory complaints would increase as a function of symptoms of depression. They also predicted that objective memory (memory tested with standardized tests and could be measured) would also be worse in people with depression considering there may be abnormalities in basic memory operations and/or in processing of emotional information.
To test the participants' symptoms of depression in the first place, the researchers used the Hospital Anxiety and Depression Scale. To test subjective memory, they simply asked the people if they experienced memory problems or not. To test objective memory, they used the delayed recall of a story from the Wechsler Memory Scale Third UK edition. And, to test the relationship between hippocampus volume and depression, they performed lab tests and MRI screenings. Through their overarching research, they also explored if subjective memory complaints were only associated with depression, or if anxiety was a factor as well. They also investigated whether symptoms of depression remained significantly related to memory after factoring in age, sex, and other items related to general cognitive ability. By exploring these other parts of their research, their results would be more significant and valid based on what they discovered after adding these to their study. They split up their 2,544 participants into different groups to test for their different hypotheses.
The results of the study revealed that more symptoms of depression were related to more frequent self-reports of memory complaints. The relationship between depression and subjective memory complaints remained significant even after adjusting for symptoms of anxiety. That indicates that their memory complaints did not appear to be due to simply reporting more problems for the sake of believing that their depression was making them that way. This led them to believe there is a possibility that depression and subjective memory reflect a negative interpretative bias (depressive realism) which suggests that people who report symptoms of depression have a higher tendency to assume ambiguous or neutral situations in a negative or threatening manner. They also found that there was no significant association between hippocampal volume and depressive symptoms, and therefore, no relation to memory performance. It was also discovered that depressive symptoms are also related to the ability to perform well on standardized tests of memory (objective memory) but that could be due to age, cognitive ability, and/or sex.
Limitations of the study include that subjective memory was only tested with a singular, basic question and levels of depression and history of clinical episodes was self-reported via questionnaires and retrospective recall.
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