Do you remember what you had for breakfast yesterday? How did you get to the university or to work? Who have you been talking 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, that is, all memories about episodes, facts and data from our lives. From our eighth birthday to the taste of an orange.

What is declarative memory

Declarative memory, also called explicit memory, is the ability to voluntarily bring to consciousness 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 give them names 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 his temporal lobes sectioned in both hemispheres. The epilepsy was successfully controlled, but something unexpected happened: he had lost many memories from eleven years ago and could not remember anything about the last two years, and was unable to create new memories. Thus, his declarative memory had been affected.

Surprisingly, it did retain the memory that stores motor skills. Riding a bike, 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 functions and anatomically independent was evidenced.

Neurological basis of declarative memory

The first difference between declarative and procedural memory is that they are located in differentiated regions . From this, it may be inferred that, on a functional level, they use different neuronal circuits and have a different way of processing information.

In the procedural memory most of the information is stored as received from the senses. We psychologists say that it is a bottom-up processing, that is, from the physical directly to the psychic. In declarative memory, on the other hand, physical data is 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 in order to store them.

In this way, the way we remember information is greatly influenced by the way we process it. This is why the internal stimuli we use when storing information can serve us to remember them again spontaneously. In the same way, the 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 form part of declarative memory are located in the temporal lobe. The most important of these are the amygdala, which plays a crucial role in the emotional processing of memories, the hippocampus, which is responsible for storing or retrieving memories, and the prefrontal cortex, which deals with the memory that stores the most short-term data.

Also included are other structures such as the nuclei of the thalamus, which connect the temporal lobe to the prefrontal, and the brain stem which sends the 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’s see each of them below.

Episodic memory

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

  • Subjective time sense
  • Awareness of this subjective time
  • A “self” that can travel in subjective time

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

Semantic memory

Tulving called the knowledge of the world – everything that is not autobiographical – semantic memory. This type of declarative memory includes all the knowledge that we can evoke in an explicit way that does not have to do with our own memories. It is our personal encyclopedia, which contains millions of entries about what we know about the world.

Contains information learned in school such as vocabulary, mathematics , some aspects of reading and writing, historical figures or dates, knowledge about art and culture, etc.