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.
Fifteen research institutes around the world, including from the US, Europe and Australia, collaborated to combine the results of their existing, smaller studies comparing the hippocampuses of depressed and healthy people.
This allowed them to examine the brain magnetic resonance imaging data of 8,927 people, 1,728 of whom had major depression and the rest of whom were healthy.
The researchers found 65% of the depressed study participants had recurrent depression and it was these people who had a smaller hippocampus, which is near the centre of the brain and is involved with long-term memory, forming new memories, and connecting emotions to those memories.
“We all have a fixed amount of information we can hold in memory at one time,” explained the study’s lead author, Nick Hubbard, a doctoral candidate at the Center for BrainHealth working with Dr. Rypma, in a news release. “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. This preoccupation of memory by depressive thoughts might also explain why more positive thoughts are often absent in depression; there simply is not enough space for them.”
“Interventions such as mindfulness-based cognitive therapy are quite successful in empowering depressed people to recognize and better regulate the content of their thoughts,” said Dr. Rypma. “Our goal is to continue to study how such therapeutic approaches can alter the depressed brain and how these alterations might result in better memory and outcomes for persons with depression.”