What is declarative memory?

This type of memory allows us to bring back to consciousness past episodes.

Do you remember what you had for breakfast yesterday? How did you commute to college or work? Who have you talked to since you woke up? If the answer is yes, it means that your declarative memory is working properly.

This type of memory, without which we could not function, stores all explicit memories, i.e. all memories about episodes, facts and data of our life. From our eighth birthday to the taste of an orange.

What is declarative memory

Declarative memory, also called explicit memory, is the capacity to bring to consciousness voluntarily episodes or facts of our life.. It is thanks to it that we can relive experiences that happened long ago, recognize faces of famous people and name them or even what we have eaten during the week.

The history of declarative memory is relatively young. Its history dates back to the studies of patient H.M. in 1957, which shed light on two questions: what components constitute memory, and where in the brain we can find declarative memory.

Patient H.M., who suffered from severe temporal lobe epilepsy, had these lobes in both hemispheres sectioned. The epilepsy was successfully controlled, but something unexpected happened: he had lost many memories from eleven years ago and did not remember anything from the last two years, and was unable to create new memories. Thus, his declarative memory had been affected.

Surprisingly, he did retain the memory that stores motor skills. Riding a bicycle, using language, etc., are skills that are stored differently because they are not data or episodes, but "ways of doing". This memory is called procedural or implicit memory. Thus, the existence of two large blocks of memory with different and anatomically independent functions was evidenced.

Neurological basis of declarative memory

The first difference between declarative and procedural memory is that they are located in differentiated regions. It follows that, at a functional level, they use different neural circuits and have a different way of processing information.

In procedural memory most of the information is stored as it is received from the senses. Psychologists say that this is bottom-up processing, i.e., from the physical directly to the psychic. In declarative memory, on the other hand, physical data are reorganized before being stored. Since information depends on cognitive processing, we speak of a top-down process. Declarative memory, on the other hand, depends on conceptually controlled or "top-down" processes, in which the subject reorganizes data for storage.

Thus, the way we remember information is strongly influenced by the way we process it. This is why the internal stimuli we use when storing information can be used to recall it spontaneously. In the same way, contextual stimuli that are processed with the data can be a source of retrieval. Some mnemonic methods exploit this feature of memory, such as the loci method.

Through the study of animals and humans, Petri and Mishkin propose that implicit and explicit memory follow different neural circuits. The structures that are part of declarative memory are located in the temporal lobe. The most important ones are the amygdala, which plays a crucial role in the emotional processing of memories, the hippocampus, which is in charge of storing or retrieving memories, and the prefrontal cortex, which deals with the memory that stores more short-term data.

Other structures are also included, such as the nuclei of the thalamus, which connect the temporal lobe with the prefrontal lobe, and the brainstem, which sends stimuli to the rest of the brain for processing. The neurotransmitter systems most involved in these processes are acetylcholine, serotonin and noradrenaline..

Two types of declarative memory

Endel Tulving, through his studies on memory, distinguished in 1972 two subtypes of declarative memory: episodic memory and semantic memory. Let us look at each of them below.

1. Episodic memory

According to Tulving, episodic or autobiographical memory consists of memory that allows a person to recall past events or personal experiences. It allows human beings to recall past personal experiences. It requires three elements:

• Sense of subjective time.
• Awareness of this subjective time
• A "self" that can travel in subjective time.

To understand how memory works, Tulving explains it by means of the metaphor of time travel. According to this metaphor, autobiographical memory is a kind of time machine that allows consciousness to travel backwards and voluntarily revisit past episodes. This is a capacity that requires consciousness and, therefore, is theorized to be unique to our species.

2. Semantic memory

Knowledge of the world - everything that is not autobiographical - Tulving called semantic memory. This type of declarative memory includes all the knowledge we can explicitly evoke that has nothing to do with our own memories. It is our personal encyclopedia, containing millions of entries about what we know about the world.

It contains information learned in school such as vocabulary, mathematics, some aspects of reading, and reading and writing.Some aspects of reading and writing, historical figures or dates, knowledge about art and culture, and so on.