How Are Episodic Memories Formed and Later Affected by Dementia?

Episodic Memories. Jose Luis Pelaez Inc Blend Images/Gety Images

What Is Episodic Memory?

Episodic memory is a part of your long term memory that recalls information about specific events or situations- thus the name "episode." Your episodic memory recalls what happened, as well as where and when the event took place.

How Episodic Memories Are Formed

According to the University of San Francisco in California, episodic memories are formed in three steps.

1) Encoding

Encoding is the process of acquiring and storing information into our memory. Not surprisingly, encoding occurs more effectively if you are paying attention to what is occurring and if you process the information more thoroughly. 

2) Consolidation

Consolidation is the process of strengthening certain pieces of information over time which allows the memory to be accessed more easily. Consolidation is assisted by repeated exposure. For example, consolidation occurs when you talk about the wedding you attended last week with others who were present. This process adds to your memory of the event and may increase or slightly shift the memory of certain aspects of the event.

3) Retrieval

Retrieval is the act of accessing the memory that was stored earlier. Think of it like a bank in which  you deposited money. It's time to retrieve that money (or memory, in this case).

Retrieval of memories is facilitated by certain cues around you, such as an emotional trigger, a picture or the music you heard at the time. Retrieval can also be made easier by the deliberate remembering of the context of what you are trying to recall, such as retracing your steps to assist you in figuring out where you may have left your car keys.

How Is Episodic Memory Affected by Dementia?

Research has demonstrated that episodic memory is affected in multiple types of dementia, including Alzheimer's, frontotemporal dementia, Parkinson's disease dementia, and Lewy body dementia.

One area of the brain significantly involved in developing and storing episodic memories is the hippocampus. The hippocampus is also an area that typically is impacted early on in Alzheimer's disease (and sometimes other types of dementia). In Alzheimer's, the hippocampus shows damage, in particular, atrophy, as the disease progresses. This correlates with a difficulty in encoding new memories into the brain.

Episodic Memory Impairment in Dementia

As an example of episodic memory impairment, consider what happens when you visit a loved one with dementia and she doesn't recall your visit later. Perhaps you had a particularly enjoyable time with her where you were able to reminisce and laugh together about the good old days.

The next day, she tells someone she misses you because she hasn't seen you for weeks.

Clearly, your visit didn't make it into her episodic memory. Does that mean it was pointless? Not worth your time or effort because she forgot it anyway?

Not at all. Although her episodic memory is impaired, her emotions still exist. Not only did she enjoy that time immensely with you, and conversely you with her, that enjoyment is likely to have lasted long after the memory of what triggered it is gone. Research has shown that the feelings created by experiences last significantly longer than the memory. Thus, her joy from your visit likely remained long after you were gone and long after she forgot you were there.

Sources:

International Journal of Geriatric Psychiatry. Volume 30, Issue 1, pages 46–54, January 2015. http://onlinelibrary.wiley.com/doi/10.1002/gps.4109/abstract

Neurology. 74, February9,2010. http://www.ftdrg.org/wp-content/uploads/Hornberger-et-al-S.51-Neurology1.pdf

Neuropsychopharmacology. 2010 Jan; 35(1): 86–104.The Episodic Memory System: Neurocircuitry and Disorders. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2882963/

University of California, San Francisco. Brain 101: Topics in Neuroscience. Episodic Memory. Accessed May 22, 2015. http://memory.ucsf.edu/brain/memory/episodic

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