In 1995 the Canadian researcher Endel Tulvig, of the University of Toronto, suggested that there are five primary memory systems.
The first is episodic memory. It allows subjects to store and become conscious of events personally experienced by them – ‘yesterday, I went to a football match with my cousin’. In a kind of way it is the support system of an individual’s history. Damaging it leads to amnesia.Semantic memory helps in acquiring general knowledge of the world. Thanks to it, we know not only that Rome is the capital of Italy and that Ronald Reagan was once the President of the United States but also that, in a restaurant, it is generally agreed that people should sit down, consult the menu, eat, ask for the bill and then pay. This memory system also incorporates a cognitive map of well-known sites – cities, houses, etc.
With a certain amount of experience a driver ends up doing technical tasks in an automatic way when a change of speed is concerned. According to Tulvig, such a process can be attributed to procedural memory, which is involved in learning new perceptive, motor or cognitive skills. Not easily rendered verbally, the knowledges stored within it involve skills that can only be acquired through physical activity. Procedural memory is the cornerstone of implicit memory (also called non declarative memory). In its perceptive components, procedural memory essentially depends on linked sensory cortexes (visual, auditory, etc.). In its motor components, where one distinguishes between the memory of motor sequences (playing a piano, writing on a keyboard) and adaptation (for example, using a joystick to follow a moving point on a screen), it depends principally on the cerebellum, the striatum and the cortext.
The fourth piece of the mnesic puzzle: the perceptual representational systems (SPR). They take in hand the job of storing the form and structure of objects, faces and words, to the exclusion of their semantic properties (significance).
Episodic, procedural and semantic systems as well as perceptual representational systems involve long term memorization. Short term memory is the privilege of the fifth basic system: the memory of work, whose mission is to keep hold of temporarily a small quantity of information in an easily accessible form during the carrying out of diverse cognitive tasks – ‘I keep in my head two numbers that need to be added up whilst I carry out the cognitive operations the calculation requires’.
Scientific literature also refers to autobiographical memory. What does it cover? Larger than episodic memory, it can be defined as the memory of all the personal information related to our pasts. In other words, it bears upon episodic memories integrated within a semantic autobiographical base, which covers general information about ourselves and the world – ‘at the time I was a young researcher at the University of Liège, I...’
Finally, declarative memory is considered in some ways as the sum combination of episodic and semantic memory. It is made up of stored explicit memories that one can access in a conscious way in the form of words. It is generally classed as explicit memory. Its principal cerebral support is the hippocampus.