Declarative memory consists of facts and events that can be consciously recalled or "declared." Also known as explicit memory, it is based on the concept that this type of memory consists of information that can be explicitly stored and retrieved.

Declarative memory differs from procedural memory, which encompasses skills such as the use of objects or movements of the body that are deeply embedded and are performed without being aware.

Declarative memory comprises episodic memory and semantic memory, and researcher Endel Tulving first proposed the distinction between episodic and semantic memory in 1972.

Examples of episodic and semantic memory

One component of episodic memory is based on specific events, or "episodes" that are part of your personal history. Some examples:

The name of your pet bird growing upYour sister’s weddingThe name of your fifth-grade teacherWhere you were when you found out about the Challenger space shuttle disasterThe other component of declarative memory is semantic memory, which is the ability to recall facts and concepts, often referred to as common knowledge. Some examples:

Understanding the difference between a dog and a catKnowing that the space shuttle Challenger disaster occurred on Jan. 28, 1986Being able to associate letters with their soundsRecalling how to use a phone

Differences between declarative and procedural memory

Procedural memory is typically acquired through repetition and practice, sometimes described as muscle memory or body memory. Also known as implicit memory, it enables us to carry out ordinary motor actions essentially on autopilot.

Usually, anterograde amnesia impacts declarative memory only and has no effect on procedural memory. An amnesiac can remember how to talk on the phone, but can’t recall with whom they spoke earlier that day.

One common example of the differences between implicit and explicit memory is that implicit memory allows you to type on a keyboard without looking at the keys, while you need explicit memory to remember that the A-S-D-F keys are on the left and J-K-L-; keys are on the right in the "home" row.

Some examples of procedural memory are:

Driving a motorcycleIce skatingRiding a bicycleShooting an arrowThese are typically tasks that you can go months or even years without performing and pick them up again quickly.

Studies of declarative memory

A 1997 study demonstrated that stress can have a significant impact on the formation of declarative memories. Participants went through a three-stage process. The first step involved memorizing a series of words; the second consisted of a stressful situation, such as public speaking or a non-stressful task; and the third asked that they remember the words from the first task. Declarative memory performance was worse in the participants that were exposed to a stressful situation after learning the words.

The chronic stress seen in those with post-traumatic stress disorder contributes to their ability to form declarative memories.

In 1953, a patient who had parts of his medial temporal lobe, hippocampus and amygdala removed to address his epilepsy was studied to determine the impact it had on his procedural and declarative memory capabilities. After the surgery, he could no longer form declarative memories but he was still able to form new procedural memories and short-term memories. This led to the understanding of the differences between procedural and declarative memories.

There have been a number of studies showing the impact slow-wave sleep on our ability to form declarative memories. Declarative memory benefits mainly from sleep periods dominated by deep slow-wave sleep, while REM sleep doesn’t appear to enhance declarative memory.