Once they enter memory, depressive thoughts can linger for long in affected people, and this extended duration may reduce the amount of information that these individuals can remember, suggests new research.
The findings have far-reaching implications for understanding how depression damages memory, as well as how depression develops and persists over the course of an individual's lifetime.
"People with depression or even healthy people with a depressed mood can be affected by depressive thoughts," explained researcher Bart Rypma from The University of Texas at Dallas in the US.
"We have known that negative thoughts tend to last longer for those with depression. However, this study is unique in showing that these thoughts, triggered from stimuli in the environment, can persist to the point that they hinder a depressed person's ability to keep their train of thought," Rypma noted.
For the study, researchers recruited 75 university undergraduate students; thirty students were classified as having depressive symptoms and 45 participants were categorised as not exhibiting depressive symptoms.
All participants were asked to respond to a sentence featuring depressive thoughts, such as "I am sad," or "People don't like me," or neutral information. They were then asked to remember a string of numbers.
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Individuals with depressed mood forgot more number strings than people without depressed mood when responding to a sentence with negative information.
"We all have a fixed amount of information we can hold in memory at one time," lead author of the study Nick Hubbard from the University of Texas at Dallas explained.
"The fact that depressive thoughts do not seem to go away once they enter memory certainly explains why depressed individuals have difficulty concentrating or remembering things in their daily lives," Hubbard noted.
The findings appeared in the Journal of Affective Disorders.