Memory

Declarative and Non-Declarative Memory

Psychologists have studied memory and learning and distinguished what appear to be different types of memory. A useful distinction for our purposes is between declarative and non-declarative memories.

In the course of our lives, we have learned many facts. We also store event memories. The memory for facts and events is called declarative memory. Declarative memory is what we usually mean by the word “memory,” but in fact we can remember many other things. These non-declarative memories fall into several categories. The type that interests us more particularly is the memory of procedures, that is, memory for ability, habits and behaviours. We learn to play the piano, to kick a ball and somehow this information is stored in our brain. Emotions, for example, are non-declarative memories.

In general, declarative memories are available for conscious evocation, and non-declarative memories are not. The tasks we learn and the emotional reflexes and associations we establish operate without conscious recognition. A non-declarative memory is also often called implicit memory, since it results directly from experience, whereas declarative memory is often called explicit memory. For it results from an effort of the conscious.

Another difference is that declarative memories are often easy to form, but also easily forgotten. In contrast, the formation of non-declarative memory attempts to require repetition and practice over a period of time, but these memories are less likely to be forgotten. While there is no clear limit to the number of declarative memories the brain can hold, there can be great variation as to the ease and speed with which new information is acquired. Studies in humans with abnormally good memories suggest that the limit for storing declarative information is quite high.

Long-Term and Short-Term Memories

Long lasting memories are those that can take days, months or years after they have been stored. However, not all memories are stored for long duration. There are great odds of a particular memories having faded. Thus, it is interesting to distinguish short-lived memories from long-lasting memories. Short memories last from seconds to hours and are vulnerable to disturbances. For example, short memories can be erased by cranial trauma or worse seizure. However, these same treatments do not affect long-lasting memories, which were stored a long time ago. Such observations led to the idea that memories would be stored in the form of short memories and gradually converted into a permanent form by means of a process called memory consolidation, which, however, does not necessarily require short memory Duration as intermediate. Both types of memory can exist in parallel.

Short-term memory often requires information to be kept in the mind. Short-term memory is usually studied by measuring the length of a randomly chosen line of numbers that a person is able to remember after hearing it: on average, we can remember about seven numbers in that list.

It is interesting to note that there are humans with cortical lesions who have normal short-term memory for information from a sensory system, but with a great deficit when information is provided by another sensory modality. These different abilities to remember lists of numbers, in different modalities, are consistent with the notion of multiple areas of temporary storage in the brain.

The Engrama

The physical representation or location of a memory is called an engram, also known as a memory trace. When you learn the meaning of a word, where is this information stored? The most frequently used technique to answer this type of question is the experimental ablation method of Marie Jean-Pierre Houreus.