Small distinction: depression is not a memory disease but mood disorders lead to memory problems. Professor Francis Eustache, neuropsychologist, directs the Inserm research unit “Neuropsychology and imaging of human memory” at the University of Caen-Normandy, and chairs the scientific council of the B2V Memory Observatory. He agreed to answer questions from Destination Santé.
How would you summarize the impact of depression on memory?
Professor Francis Eustache: “I would say that it is a memory that is less available and oriented towards negative content which leads to dark thoughts. Because in addition to the temporary alteration of memory mechanisms, the contents can be modified. Dark thoughts invade memories which, in turn, invade the thoughts of the depressed person. It’s a vicious circle.
Overall, depression can lead to memory problems due to difficulty concentrating, sleep disturbances, and ideomotor slowing. The latter term means that the depressed patient feels difficulty in expressing his ideas and does so slowly. His verbal flow is also slowed down: the slowdown concerns both the movement of ideas and their expression in language. »
How can depression affect memory?
Professor Francis Eustache: “Depression can affect memory in different ways, through difficulty concentrating, but also in maintaining attention on completing tasks. This can make it difficult to remember new information. Depressed people may also have difficulty using their so-called “working” memory, which can affect their ability to solve problems and retain information in the short term.
Depression can also lead to “autobiographical” memory distortions, where personal memories are tinged with negativity. Hence a selective recall of negative memories and a loss of positive memories.
Episodic memory, responsible for recalling specific events, is also affected: depressed people have difficulty remembering details of past events due to disturbances within this memory.
Furthermore, sleep disorders, common in depressed people, affect the consolidation of long-term memory. This means that the creation of new memories may be compromised. »
How do you know if memory problems are linked to depression or a sign of Alzheimer’s disease?
Professor Francis Eustache: “In Alzheimer’s disease, we observe genuine memory disorders, that is to say that the person is unable to record new information, while forgetting information and memories. Neuropsychological tests, used in “Memory Consultations”, make it possible to specify the stage which is altered in the formation of memories: encoding (or recording), storage, and retrieval (or recall).
On the other hand, in depression, information is memorized but it is sometimes difficult to access. This is why we rather speak of “apparent” memory disorders, because it is enough for the patient to have the right recall cues (the beginning of the words presented in the encoding phase or their semantic category: “it was a name of animal, fruit”, etc.), so that he can find the information. Conversely, these clues are of little help to patients suffering from Alzheimer’s disease.
Another notable point in the depressive state is the distortion of the perception of time and projection into the future. The depressed person feels like time is speeding up. Episodic biographical memories are rare, blunted and “overgeneralized” (exaggerated generalization), because the depressive is withdrawn with blunted emotion and focused entirely on sadness. »
Does the person regain their memory abilities once the depressive episode has resolved?
Professor Francis Eustache: “Research in neuroscience, which notably uses functional brain imaging methods, is moving in the same direction as clinical descriptions. All show a dysfunction of the circuits which unite the prefrontal regions (in front of the brain) and the hippocampi, involved in episodic memory.
Conclusion: in depression, it is not really the memory mechanisms that are affected, but more the strategies that allow the memory to function well. Don’t worry, however, the person regains good memory abilities, which suggests that the alterations are reversible. »
To know more : Eustache F and Desgranges B, The new paths of memory, Paris, Ed. Le pommier, 2020.