Combining two treatments may prevent the cognitive decline associated with major depressive disorder
Major depressive disorder (MDD) has been associated with cognitive impairment and a higher risk of dementia. There are no proven treatments to slow cognitive decline or prevent the onset of dementia. These risks remain even in cases where the symptoms of MDD have subsided, called remitted MDD (rMDD).
There’s evidence indicating that transcranial direct current stimulation (tDCS) or cognitive remediation (CR) have modest positive effects on cognitive abilities when used alone.
tDCS uses constant, low direct current delivered via electrodes on the head to alter nerve activity in the brain. CR is a set of memory exercises and techniques that aim to improve cognitive functioning in areas such as attention, working memory, and planning. CR typically takes the form of learning activities designed to teach ‘thinking skills’, varying based on the needs of the patient.
Despite the potential of these treatments, there has never been a major study that has provided tDCS and CR together to people with rMDD to test if they are effective in slowing cognitive decline.
Dr. Tarek Rajji, Dr. Benoit Mulsant, and their team conducted a study to determine if a combination of CR and tDCS could slow cognitive decline in older adults with rMDD or mild cognitive impairment (MCI). We spoke to them about their research and what they discovered.
What motivated this research?
TR & BM: Remitted Major Depressive Disorder (rMDD) has been associated with cognitive impairment and a higher risk of dementia. Until now there have been no evidence-based treatments to mitigate cognitive decline and prevent the onset of dementia. Because both tDCS and CR have been associated with modest cognitive improvement when applied on their own, we hypothesized that if we combined them, we could slow the cognitive decline associated with rMDD.
What was the most important finding of this study, in your opinion?
TR & BM: We followed 375 older patients who were at risk of developing dementia due to rMDD or Mild Cognitive Impairment (MCI) for up to seven years. On average, cognitive decline took three years longer to progress among those who received tDCS and CR, compared to those who did not. Those that received the treatment also experienced some unique benefits to executive function and verbal memory. These positive results were primarily experienced by those with rMDD, regardless of whether or not they also had MCI.
How does this change treatment in the future?
TR & BM: If our main finding is confirmed, we could have a non-invasive intervention that will slow down cognitive decline and prevent the onset of dementia in older patients with rMDD.
Any next steps?
TR & BM: We hope to receive funding to conduct a randomized, controlled trial with a large and diverse population of patients to confirm our findings.
What is the major take home message for the public?
TR & BM: The study showed that a combination of CR and tDCS effectively slowed cognitive decline in older adults with rMDD. If further study confirms these results, it will mean we have identified a method to proactively prevent cognitive decline for those with rMDD and allow them to maintain their cognitive abilities and independence for longer, greatly improving their quality of life.
Read this month's impact paper.
Rajji TK, Bowie CR, Herrmann N, et al. Slowing Cognitive Decline in Major Depressive Disorder and Mild Cognitive Impairment: A Randomized Clinical Trial. JAMA Psychiatry. 2025;82(1):12–21. doi:10.1001/jamapsychiatry.2024.3241
