By American Geriatrics Society (AGS)

A fully functional memory is vital for human existence. That’s because without some way of remembering what’s happened, every waking moment stands alone as a brand-new experience; you have no past and can’t plan for the future. Sadly, memory is one of the main casualties of the different dementia processes.

Two main types of memory exist: short-term and long-term memory. You also possess an emotional memory, which is completely preserved in dementia.

  • Short-term memory: Short-term memory is your working memory, which stores information for a short time only (hence its name) before it’s either forgotten or transferred to long-term memory for storage, potentially for the rest of your life. Short-term memory, it’s believed, allows people to remember lists of only seven to nine items, for around 30 seconds. Repeating these items over and over in your head can help keep them there, but if you’re distracted by something else or the 30 seconds run out, the items are gone.
  • Long-term memory: Long-term memory has unlimited capacity, and memories can be stored until your dying day. It has two main forms:
  • Declarative memory: This is memory for facts such as bank account or phone numbers, computer passwords, meanings of words, general knowledge, and events in your past.
  • Procedural memory: This allows you to remember how to carry out tasks without having to relearn them each time. It’s what makes riding a bike easy when you haven’t done it for a while. And it’s what enables you to know how to hold a knife and fork each time you pick them up, or to brush your teeth using the same technique each day.

The development of a long-term memory in the brain involves three crucial steps. If any of these steps don’t work, the memory is effectively lost — and that’s what can happen in dementia:

  • Encoding (which ensures that all types of sensory input are in a suitable form for storage)
  • Storage
  • Retrieval

Encoding can be thought of as the way in which the nervous system labels a fact, emotion, smell, image, or whatever is to be remembered so it can be stored for further use. It’s very similar to the way in which librarians assign specific numbers to books depending on their subject matter so someone searching for them among the many bookshelves can easily find them.

Emotional memory allows you to recall the really important moments in your life, both good and bad. It stores not only the information about what happened, but also an exact memory of how you felt. It means that if you find yourself in a similar situation in future, you’ll probably experience those feelings again.

Classic short- and long-term memories are created in a part of the brain called the hippocampus, and long-term memories are stored in different parts of the outside of the brain called the cerebral cortex. Cells in these areas and those that communicate between them can be damaged in dementia, stopping the encoding, storage, and retrieval processes.

In contrast, emotional memory appears to occupy much more primitive parts of the brain, particularly in the brain stem. These areas aren’t affected by dementia, meaning that emotional memory can remain intact.

The implication here is that people with dementia can still be troubled by stored memories of negative events, such as the experience of being beaten by a parent as a child. If, because of dementia, a person believes that a long-dead father is still alive, that person may experience some strong negative emotions. Likewise, an action carried out in the present, such as an injection, that provoked an unhappy response in the past may cause the person with dementia to respond negatively to it. These emotional memories are thought to lead to some of the disturbed and aggressive behavior seen in people with dementia.