Neural Pathways to
Long term memory
Presented by: Gerald Lai, Scott Nisbitt, Ed Fong, Phat Ha

What is declarative memory?

Declarative memory is our memory for facts (Tulving & Schater, 1990). There is a common belief that declarative memory is further broken down into two components: Episodic memory (memory for past and personally experienced events), and Semantic memory (knowledge for the meaning of words and how to apply them).

What physical area of the brain is declarative memory associated with?

In general, the hippocampus and temporal cortex. More specifically, declarative memory primarily involves the diencephalon of the brain (Long, 2000). This portion of the brain refers to the anterior to midbrain regions and is comprised of the thalamus and hypothalamus. The two additional areas that are associated with declarative memory are the peripheral cortex and the amygdala (Long, 2000).

Another area that is associated with declarative memory is the neocortex. In particular, this includes the right frontal & temporal lobes for the episodic component, and the temporal lobes for the semantic component (Long, 2000).  awaiting images from Ed

Why is declarative memory further broken down into episodic and semantic components?

The psychologist who first proposed this idea was Endel Tulving. For episodic memory, Tulving notes that the subject not only has the memory, but can remember something about the setting in which the memory was learned. Conversely, for semantic memory, the subject cannot recall the context of the initial learning.

Tulving argued that episodic memory was the system that was tested in most memory experiments which required subjects to recall lists of words (Allard, 2001). He reasoned that if a subject failed to recall a word in a particular list, it was due to the fact that he/she failed to recall a particular episode (i.e., list) and not the meaning of the word. Recall that semantic memory can be defined as the knowledge for the meaning of words and how to apply them. This caused Tulving to make the distinction between memory for ‘meanings’ (semantic) versus memory for ‘episodes’ or experiences (episodic).

What evidence is there of declarative memory?

Studies of amnesiacs have been the most common form of evidence used to distinguish declarative memory from the other prominent type of LTM known as procedural memory. Amnesiacs are known to lack the ability to add to their declarative memory stores (episodic or semantic). 

A well-known case in history involves the patient known as HM, who had his anterior and medial portions his temporal lobes removed to prevent epileptic seizures (Corkin, 1968). HM and similar patients have normal memory for events before their trauma but they can't form new long-term memories. This suggests that the frontal and medial temporal lobe structures are required for adding information to declarative memory. Several researchers have accepted this case as support for the distinction of memory pathways.

Other studies, such as the one by Cermak, Lewis, Butters and Goodglass (1973), have used Korsakoff patients to show the distinction between declarative and procedural memory. This study examined their learning performance on a declarative task (finger maze) vs. a procedural task (pursuit rotor). The normal learning shown by Korsakoff patients in the pursuit rotor task, together with the impaired performance on the finger maze, is further evidence to support the dissociation between the declarative and procedural pathways. 

Separate learning patterns observed in Korsakoff patients were also reported by Cohen and Squire (1980). Their testing of mirror reading skills suggested that amnesiacs are able to acquire mental operations involving learning rules or procedures, but operations involving specific, declarative, data based information cannot be remembered (Allard, 2001). On the other hand, learning of pattern recognition was observed and attributed to the use of procedural LTM, thus, another indication of distinct pathways.

Further evidence for the existence of declarative memory is shown by priming experiments, such as the one by Jacoby & Witherspoon (1982). In this study, amnesiacs and normals (control) were asked general knowledge questions, for example, “who is the heir to the British throne?” or “name a musical instrument that has a reed?”. The subjects were then given a spelling test using homophones of words (i.e., heir/hair, reed/read). Both amnesiacs and normals were observed to spell the correct version seen in the questions presented (heir & reed) even though these were the less commonly used versions. Jacoby & Witherspoon (1982) reasoned that these observation of word priming utilizes semantic memory (i.e., recall meaning and application rules for words) in order to select the correct spellings. Therefore, declarative memory is present and being used.