The 4 Distinct Memory Processes and Memory Dysfunction
By: Sex Carl @SexCarl
Dysfunction in memory processes can be an incredibly disabling feature of numerous pathologies. The most obvious for most people are neurodegenerative diseases such as Alzheimer’s disease. Recently in the New York Times was an article describing the upcoming increase in cases, a devastating disease course, and an insurmountable financial burden that lies ahead, coupled with an awful emotional burden to patients, families, and the healthcare industry as a whole. But, a wide array of different pathologies can affect memory function, including strokes, hypoxia, recent surgeries, various medication side effects, mental health disorders such as ADHD, depression and anxiety, and of course a normal age progression often leads to memory impairment. Traditionally people classify memory into two categories; A “short-term memory” and a “long-term” memory. A combined increase in neuroscienice studies, working with specific brain lesions, and an overall better understanding of PET, fMRI, and EVP technologies has led to a classification system breaking down memory processes into four categories.
- Episodic Memory: The episodic memory system refers to one’s ability to recall personal experiences framed in our own context. Examples of every-day episodic memory processes include remembering a short anecdote a friend told you, or recalling what you did for Independence Day last year. Episodic memory is both explicit and declarative, meaning one is conscious of this memory, and is able to declare the memory, or recall it. The episodic memory system primarily relies on function from the medial temporal lobes (including the hippocampus), the basal forebrain with the medial septum and diagonal band of Broca’s area, the retrospelenial cortex, the presubiculum, the gornix, mammillary bodies, the mammillothalamic tract, and the anterior nucleus of the thalamus (Budson, Price 2005). An interesting fact is that the frontal lobe is also critical for episodic memory, for it is the frontal lobe that allows us to focus on the information we hope to store into our episodic memory. A dysfunction in the frontal lobe can lead to a disruption in the encoding of our episodic memories, and lead to false memories, confabulations, or remembering stories with incorrect details. Budson and Price compare the function of the frontal lobes in regards to episodic memory as a “file clerk” taking memories from the MTL (a “recent memories file cabinet”) and correctly assigning those memories to other cortical regions. Thus, any dysfunction in this pathway from event to an episodic memory can disrupt memory function. Many different diseases and disorders can effect episodic memory, including those mentioned before, Korsakoff’s syndrome, hypoglycemia, and even concussions.
- Semantic Memory: Semantic memory processes can best be described as a general knowledge of concepts and facts. It is both explicit and declarative in nature. For example, what a tiger looks like, and how many stars are on the United States flag. Because semantic memory could call on episodic memories to know facts about it, it is likely that many different cortical regions are involved in semantic memory. But, constricting the scope of semantic memory to purely naming and conceptual facts, semantic memory is localized in the inferolateral temporal lobes of the brain. Again, neurodegenerative disorders, TBI, and other conditions can affect ones semantic memory process.
- Procedural Memory: Procedural memory refers to the way in which we algorithmically learn behaviors that are often used at an automatic and unconscious level. A common example of this is riding a bicycle, knowing how to dial keys on a telephone without looking at them, or using a manual transmission vehicle. Procedural memory can be explicit, in the case of one learning how to use a manual transmission versus someone who has driven one for twenty years. Procedural memory can often be retained in those showing episodic memory deficits, showing that procedural memory is separate and distinct. Brain imaging studies show that procedural memory lies within the basal ganglia, cerebellum, and supplementary motor area. Dysfunction in procedural memory may present as someone who suddenly loses the ability to perform previously automatic tasks like playing an instrument, writing, or swinging a golf club. Two of the most common diseases that affect procedural memory processes are Parkinson’s disease and Huntington’s disease.
- Working Memory: Finally, working memory. Working memory is a fascinating combination of attention, concentration, and short-term memory processes. It requires constant maintenance and manipulation of information, and it is an explicit and declarative process. Within working memory, it can be broken down into two components: phonological information and spatial information. Phonological information could be remembering someone’s phone number in your head, while spatial information is mentally following a route, or visualizing the manipulation of an object. Working memory requires the work of the prefrontal cortex of the brain, a region responsible for complex cognitive processes. Because working memory calls on many regions of the brain, and because working memory is complex, many neurodegenerative diseases impair the working memory.
Sources: N Engl J Med 2005;352:692-9.
Latest posts by Sex Carl (see all)
- The 4 Distinct Memory Processes and Memory Dysfunction - May 19, 2013