What are the long-term impacts of depression on short-term memory?

July 2021

Answered by: Laurence Messier, Master's student in Neuroscience

Depression is a psychiatric illness affecting an estimated 322 million people globally, making it one of the leading causes of disability worldwide¹. Although depressive disorders are often associated with mood-related symptoms, such as severe sadness or a general loss of interest, depression can also cause a range of other symptoms that are less well known, but just as real²! For example, this illness can affect cognition, which includes all of our brain's abilities to learn and understand³. Memory is one of our cognitive faculties and can be affected by depression, a fact that has been well documented³. Indeed, memory problems are quite common in people living with depression and they tend to increase with the severity of the depressive symptoms experienced⁴. Several types of memory can be affected, which explains why people living with a depressive disorder have difficulty remembering specific details or tend to remember negative events better than positive ones³.

But what about short-term memory specifically? Several studies have shown that depression can affect short-term memory, the type of memory that allows us to retain a limited amount of information in a short period of time. For example, a group of researchers published their study in 2013 and found that the more severe the depressive symptoms, the more difficult it was for the participants to perform a task that assessed their associative memory abilities⁵.In this task, participants were shown a series of images representing objects that are seen daily. However, there was a catch: some of the images could either appear only once, or appear twice, or could be replaced by a similar image. The participants' goal was to remember whether or not they had already viewed an image or if they had already viewed a similar one during the task.In this task, participants were shown a series of images representing objects that are seen daily. However, there was a catch: some of the images could either appear only once, or appear twice, or could be replaced by a similar image. The goal of the participants was to remember whether or not they had already seen an image or if they had already seen a similar one during the task. After analyzing the results, the researchers observed that the depressed participants did less well than the other participants, indicating that their condition had an impact on their memory.

But how are memory and depression related? Unfortunately, science has not yet fully answered this question. However, our brains can give us some clues to find an answer! Indeed, several research groups that have studied the subject have found that several parts of the brain are altered physically and in their functioning in the context of depression⁶. For example, the prefrontal cortex, the part of our brain that is located just behind our forehead, does not function the same way in people living with depression as it does in people without a psychiatric illness⁶. In fact, this part of the brain, which is associated with short-term and long-term memory, shows reduced activity in these individuals. Another example is the hippocampus, a tiny structure found in each hemisphere of our brain. Indeed, it is atrophied in people living with depression⁷. Although it is not yet known whether this illness has an influence on the size of the hippocampus or vice versa, one thing is certain: this brain structure plays an important role in learning, but also in memory⁶. Indeed, the hippocampus allows the brain to transform short-term memories in order to store them in our long-term memory⁸. It is worth noting that even after the remission of a depressive disorder, the hippocampus does not tend to return to its previous size⁹. This may partially explain why memory-related symptoms may persist even after all other depressive symptoms have resolved¹⁰.

References

1. Organization, W.H. Depression and other common mental disorders: global health estimates. (World Health Organization, 2017).

2. Otte, C., et al. Major depressive disorder. Nature Reviews Disease Primers 2, 16065 (2016).

3. Rock, P., Roiser, J., Riedel, W. & Blackwell, A. Cognitive impairment in depression: a systematic review and meta-analysis. Psychological medicine 44, 2029-2040 (2014).

4. Schweizer, S., Kievit, R.A., Emery, T., Cam, C.A.N. & Henson, R.N. Symptoms of depression in a large healthy population cohort are related to subjective memory complaints and memory performance in negative contexts. Psychological medicine 48, 104-114 (2018).

5. Shelton, D.J. & Kirwan, C.B. A possible negative influence of depression on the ability to overcome memory interference. Behavioural Brain Research 256, 20-26 (2013).

6. Palazidou, E. The neurobiology of depression. British Medical Bulletin 101, 127-145 (2012).

7. Masi, G. & Brovedani, P. The Hippocampus, Neurotrophic Factors and Depression. CNS Drugs 25, 913-931 (2011).

8. Hartley, T., et al. The hippocampus is required for short-term topographical memory in humans. Hippocampus 17, 34-48 (2007).

9. Santos, M.A.O., Bezerra, L.S., Carvalho, A.R.M.R. & Brainer-Lima, A.M. Global hippocampal atrophy in major depressive disorder: a meta-analysis of magnetic resonance imaging studies. Trends in psychiatry and psychotherapy 40, 369-378 (2018).

10. Semkovska, M., et al. Cognitive function following a major depressive episode: a systematic review and meta-analysis. The Lancet Psychiatry 6, 851-861 (2019).