There are different “types” of memory that are not all affected in the same way by Alzheimer's disease, according to our partner The Conversation.
Memories of lived events are thus linked to “episodic memory” while memories of general knowledge are linked to “semantic memory”.
The analysis of this phenomenon was carried out by Émilie Delage, doctoral student in neuropsychology at the University of Montreal, Isabelle Rouleau, full professor of the Department of psychology - Neuropsychology section - at the University of Quebec (Montreal) and Sven Joubert, professor holder of Neuropsychology of Aging at the University of Montreal.
Alzheimer's disease, this neurodegenerative dementia that affects memory, is unfortunately well known to the general public.
In Canada, more than half a million people live with this dementia, and this number is expected to double over the next ten years, especially as the population ages.
35.6 million people live with Alzheimer's disease worldwide. There will be 65.7 million patients in 2030 and 115.4 million in 2050 (prospective: World Alzheimer Report 2010) © Lamiot / Wikipedia CC BY-SA 3.0
Alzheimer's disease is feared: we accuse it - sometimes as a joke - when we forget to buy an item at the grocery store, we worry about it when we can no longer find the name of the actor. 'a film, we recognize it by seeing a disoriented elderly person.
However, do we really know the behaviors that make it possible to diagnose Alzheimer's disease?
I am completing my second year of a doctorate in clinical neuropsychology at the University of Montreal, at the Laboratory of Neuropsychology of Aging of the Research Center of the University Institute of Geriatrics of Montreal (CRIUGM).
I am studying this question and the answer is not that simple.
We obviously know that Alzheimer's disease affects memory.
Except that, wrongly, we often imagine memory as a large whole, considering it as a single basket where all our memories are piled up.
It is therefore first important to understand that there are different types of memory, and to what extent they are affected in Alzheimer's disease.
Episodic memory
There are several types of memories.
The first category includes personal memories of events that we have experienced since the beginning of our life.
A bit like a photo album, episodic memory brings together memories of our childhood, our first move, our best trip, but also our last weekend and what we ate for lunch this morning. .
These are the memories which, to be recalled to the surface, require that we make a sort of "mental journey" in time to place themselves in the context of the event experienced (when was it? ? with whom ?).
Semantic memory
Unlike episodic memory, semantic memory groups together memories that do not need to be reactivated by placing themselves in context.
We are talking here about general knowledge about the outside world, which is not linked to a specific place or time.
For example, if we are wondering which animal has a shell, or who Celine Dion's husband was, we don't need to think about a specific time in our life to find the answer.
We do not specifically remember the context in which we learned this, but this general knowledge is embedded in our memory.
Signs and symptoms of Alzheimer's disease © fondation-alzheimer.org
Distinct regions of the brain
Obviously, these two types of memory are closely linked in our daily life.
We are constantly using our episodic and semantic memories to function, and, at the same time, we are continually encoding new episodic and semantic memories.
Despite the fact that they are related, these two types of memory are nevertheless underpinned by partially distinct regions in the brain.
The fabrication of memories of lived events (related to episodic memory) involves the hippocampi, structures of the internal temporal lobe, located in the middle of the brain, as well as the frontal lobe which serves to put it all in context.
General knowledge memories (related to semantic memory), on the other hand, involve more the functioning of the parahippocampal regions, that is, the structures located just around the hippocampi and the anterior part of the temporal lobes (temporal poles). .
The hippocampus underlies episodic memory, while parahippocampal regions, such as the perirhinal cortex (here in green), underlie semantic memory © democritique.org
What about Alzheimer's disease?
And so, between forgetting the film watched the day before or mixing up the names of singers, what is more worrying?
Typically, Alzheimer's disease is associated with a decline in episodic memory.
Patients will complain that they no longer remember the events they went through, the conversations they had, the things they did.
It is this type of memory that is most often tested in neuropsychology when evaluating dementia, and it is also this type of memory that is studied in the vast majority of research on Alzheimer's disease.
However, a new paradigm is emerging in clinical research, particularly in the laboratory where we conduct our research.
Recent studies show that in fact, it is the semantic memory that is affected first in the course of Alzheimer's disease.
We note that even before forgetting their memories of lived events, patients show a gradual decline in their general knowledge.
Different tests can be used to assess cognitive functions, including recognition of links between different objects © Shutterstock (via The Conversation)
For example, they have more difficulty than healthy seniors in naming celebrities, like Albert Einstein, or well-known logos like Pepsi or Desjardins.
They also find it difficult to answer questions about the biography of these celebrities (for example, whether Maurice Richard was, yes or not, a singer), to answer specific questions about objects or animals (was he the ostrich runs, flies or swims?) or to recognize objects such as a harmonica, a helicopter or an igloo from a drawing.
Symptoms 12 years before
According to a study that evaluated several hundred elderly people on different cognitive functions, individuals who will develop Alzheimer's disease begin to have deficits in semantic memory up to 12 years before being diagnosed with dementia. The difficulties of semantic memory thus arise before the forgetting of the lived events, the spatio-temporal disorientation, the loss of personal effects or the difficulties of the speech.
However, these deficits are rarely reported by patients when they complain about their memory, as they usually find a way to compensate for these difficulties in their daily life.
They will use portfolios like "thing" or "trick" to describe concepts they can no longer name.
This explains in particular why semantic memory has been little studied in connection with Alzheimer's disease.
Alzheimer's disease: infographic © Institut Pasteur de Lille
Above all, do not be alarmed
It is common that as we age, we worry about our memory and we fear Alzheimer's disease. This is perfectly normal. In clinical neuropsychology, we even see that many elderly people complain about their memory, even those who ultimately have no difficulty! We should therefore not be alarmed at the slightest oversight, because subjective complaints are not necessarily linked to real deficits. These complaints may, for example, be associated with the presence of anxiety or depressive symptoms or a feeling of loneliness.
Despite everything, knowing the first signs of Alzheimer's disease allows us to be on the lookout for the first manifestations in ourselves and our loved ones.
When we notice that we have more and more often the words "on the tip of the tongue", that we can no longer tell stories as precisely as before or that we have difficulty naming or to use certain everyday objects - and whether this worries us or worries our loved ones - it may be relevant to schedule a visit to the doctor or neuropsychologist.
Our “Alzheimer's disease” file
Fortunately, there are actions that can be taken to support our cognitive health.
First, intellectual stimulation is important: reading books, doing sudokus, crosswords or puzzles, playing board games and doing social activities are examples of activities that can improve our resistance to develop cognitive impairment.
Also, the hygiene of life counts for a lot.
Getting regular physical activity, eating a healthy diet, and maintaining good sleep habits is beneficial for both physical and cognitive health.
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This analysis was written by Émilie Delage, doctoral student in neuropsychology at the University of Montreal, Isabelle Rouleau, full professor in the Department of Psychology - Neuropsychology section - at the University of Quebec (Montreal) and Sven Joubert, full professor of Neuropsychology at the aging at the University of Montreal.
The original article was published on The Conversation website.
Declaration of interests
Émilie Delage has received funding from the Canadian Institutes of Health Research, the Research Center of the University Institute of Geriatrics of Montreal, as well as the Alzheimer Society Canada.
Dr Isabelle Rouleau received a grant from the Alzheimer Society for a project on semantic memory disorders in the prodromal phase of Alzheimer's disease.
Dr Sven Joubert received a grant from the Alzheimer Society for a project on semantic memory disorders in the prodromal phase of Alzheimer's disease.
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