Memory is the cognitive ability to encode and store information and to recall it later.
If we want to talk about memory, a clear terminology is required. That is why psychologists have divided memory into different structures. One of the most popular theoretical frameworks is the differentiation between short- and long-term memory. However, experts have further specified this model. For example, today working memory is typically included in the structure. Working memory refers to the treatment of information several seconds ago and “works” with all the very recent information that are needed at the present time to solve a specific task. The working memory model has first been introduced by Baddeley and Hitch (1974). The authors assumed that working memory consists of four different capacities including a phonological loop where verbal information is held due to rehearsal or the visuo-spatial sketchpad which was assumed to store information by an internal representation of the visuo-spatial details.
Moreover, further differentiations also exist for the long-term memory. It is differentiated into declarative and non-declarative memory based on the content. The non-declarative long-term memory stores content that is difficult to verbalize, such as riding a bicycle. Non-declarative memory is known to be more robust against forgetting. The declarative memory, on the other hand, includes the episodic and the semantic memory. Episodic memory refers to information of oneself such as remembering your first day at school or what you ate yesterday. Semantic memory consists of information that includes everyday knowledge. This includes, for example, facts about the world we live in stemming from history or politics or numerical knowledge. Impairments in declarative memory are associated with many neurodegenerative diseases – the best known of which is Alzheimer’s disease. (For interested readers: In addition to this standard classification, the term “source memory” has also been established. This refers to the ability to recall the context of the memory in addition to the actual content. Exciting effects such as the “cheater bias” are associated with source memory.)
But where do all these activities take place?
There is consensus that the medial temporal lobe, particularly the hippocampus, is involved with memory functions. The structure looks like a seahorse and is located in the limbic system of the brain. It contains different layers and is well connected with other structures like the amygdala, the entorhinal cortex or the cingulate gyrus. Its role in memory has been investigated vastly. If you search for “hippocampus and memory” on Google Scholar, you get 1,400,000 results. If you enter “medial temporal lobe and memory” in the search bar, you receive 381,000 results (and note that the hippocampus is placed in the medial temporal lobe). “Basal ganglia and memory” yields only 256,000 hits. In Alzheimer’s disease the hippocampus is known to be one of the first structures affected by neuropathologies. In fact, already at a presymptomatic stage, changes in the hippocampus are evident, which are accompanied by deteriorations in memory functions. Looking for mild cognitive decline in declarative memory performance therefore represents one of the most promising approaches to detect early-onset Alzheimer’s (Click here to learn more about a way to model early Alzheimer´s symptoms.)