People who suffer from depression or experience depressive thoughts frequently have problems with concentration and memory. They often forget sentences they’ve just read, lose track of assignments at both work and home, and make basic mistakes that they wouldn’t make otherwise. Researchers theorize that this is because people with depressive thoughts maintain attention on said thoughts, preventing them from adding anything new to their cognitive load. In other words, depression gums up the brain.
A recent study published in the journal Cognition & Emotion has lent more evidence to the theory that depressive thoughts inhibit clear thinking. Inspired by the memory problems and reduced concentration observed in people with depression, Nicholas A. Hubbard and his colleagues set out to observe the effect of depressive thoughts on working memory. They performed three separate studies. In the first study, they tested whether people with dysphoria – a significant and prolonged depressed mood state that does not necessarily meet the criteria for clinical depression – could maintain as much goal-related information in their minds as individuals in the control group. In the second study, they tested whether or not people with dysphoria could still maintain that information when bombarded with depressive thoughts. In the third study, the researchers examined whether or not cognitive processing speed was the same in people with and without dysphoria.
First study tests neutral memories
In the first study, participants were instructed to memorize a list of numbers in what is known as an R-span task. After seeing one number but before seeing the next, participants had to perform what is known as an “interference task,” or a task designed to draw their attention away from the main task. In this interference task, participants had to judge whether or not a presented sentence made sense (e.g., “Most people agree the Monday is the worst stick of the week.”) before returning to the number task. They then had to recall the numbers while ignoring the sentences. People with dysphoria and people without dysphoria performed exactly the same, demonstrating that, in this case, working memory was not harmed in people with depressive thoughts.
Second study tests depressive memories
In the second study, a new group of participants performed the number memorization task. This time, however, the interference task was not a neutral sentence judgment task; it was instead a negative sentence judgment task. Participants were presented with a sentence congruent with depression (e.g., “I feel discouraged about my future.”) and asked to judge whether or not they had experienced this thought recently. This was known as the D-span task. In contrast with the last study, participants with dysphoria performed significantly worse than participants without dysphoria. Researchers theorized that this was because dysphoric patients were unable to effectively push the negative thoughts from their minds. This theory is consistent with results from another study in which people with depression found it more difficult to discount negative words in an irrelevant information task. When provided with lists of to-be-remembered words and to-be-forgotten words, people with depression were more likely to accidentally remember negative to-be-forgotten words than people without depression.
Third study tests processing speed
In the third and final study, the researchers chose to investigate whether or not cognitive processing speed impacts D-span performance for people with dysphoria. This was accomplished by having participants perform a processing speed task and then examining correlations between processing speed and performance on the depressive working memory task. Sure enough, people with dysphoria had a processing speed that correlated with D-span performance, whereas people without dysphoria had no such correlation. This suggests that people with dysphoria are forced to rely on additional cognitive processes to perform the D-task, whereas people without dysphoria are not.
Insight for clinicians
These three studies provide additional evidence that depressive thoughts disrupt working memory in individuals with depression and dysphoria. What does this mean for treating depression? Understanding precisely how depressive information disrupts working memory can help clinicians design therapies for patients who are struggling with the memory and concentration problems inherent in depression. Cognitive training that strengthens working memory while drawing resources away from depressive thoughts might be key to improving the quality of life for depressed and dysphoric patients.