What Is the Decay Theory?

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  • Written By: Mary McMahon
  • Edited By: Nancy Fann-Im
  • Last Modified Date: 12 October 2019
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Decay theory is a belief in some areas of the cognitive psychology community that memories fade over time, especially with disuse. This is particularly important for short term memory, which only lasts for a limited period of time to begin with. Researchers who focus on memory are interested not just in how people acquire and retrieve memories, but in how they forget things. The study of forgetting includes explorations of decay theory and other theories to explain how people forget information after they store it for future reference.

Since the early 1900s, researchers on cognition have proposed various “use it or lose it” explanations for forgetting. Researchers argued that when a memory wasn't accessed, the brain might discard it in lieu of material it does use, or might lose the pathway it uses to get to that memory. Other researchers are skeptical about decay theory and believe that it cannot be categorically proved. It is a difficult topic of study because many of the mechanisms of memory retrieval cannot be quantitatively measured.


One explanation for decay theory that relies on actual physical evidence involves the gradual degradation of the brain over time. As people age, their neurons start to die off, especially if they have degenerative neurological diseases, brain injuries, or lifestyle factors that contribute to neuron death, like a history of drug use. With the death of neurons in the brain, it may be possible to lose memories along pathways that are no longer accessible. Memory is distributed across the brain, but if enough information is lost, the brain might not be able to reconstruct a memory in a meaningful way.

Researchers with an interest in decay theory can test how it operates in the short term memory by having subjects perform a memory task. Subjects may be exposed to various stimuli like words, symbols, or numbers they are asked to memorize. The test can determine how well they recall those items after a set interval. Researchers can change variables by doing things like having subjects rehearse the memories to determine if accessing them and focusing on them increases the chance of memory retention.

People with an interest in ongoing research into memory and the process of forgetting can access the latest research through a number of publications. Psychologists, neurologists, and other researchers with an interest in memory are always embarking on new studies and reevaluating old ones. People living in communities where research is taking place may be able to contribute by volunteering for studies.


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Post 12

@MrMoody - What you’ve described is similar to a concept on forgetting I’ve heard about called interference theory. Basically interference theory says that new stuff you learn “interferes” with old stuff you learned on the same subject, or vice-versa.

In other words, the brain has room for only one version of that information you’re studying. You can’t have version 1.0 and version 2.0 all stored in the same brain.

I think it’s a stretch to argue that actually, because people do study things like the evolution of ideas, where they have to file away in their head the different manifestations of an idea over time.

Still, unless you are doing that deliberately, I think the brain does choose the most recent version of an idea and conveniently forgets the old one.

Post 11

@miriam98 - I don’t know if it’s science or not, but I once read that the brain has to forget things over time.

The reason is that we accumulate so much information, that if we didn’t forget certain things, we would suffer from sensory information overload. I don’t know if that is true but it certainly makes sense.

Why would you want to remember everything? As time goes on and you head into your retirement years, fewer things become important anyway.

Post 10

Decay theory psychology does have some basis in fact, in my opinion. The article states that it’s difficult to measure memory quantitatively, and that is true.

However, it’s also true that if you keep yourself mentally active as you grow older, you minimize the possibility of getting Alzheimer’s or Parkinson’s or things like that, both conditions which are characterized by forgetfulness.

Scientists say you should keep doing something – anything, like reading, learning a new skill, anything that engages the brain – well into your older years. This acts as an offset against mental deterioration and keeps you sharp and alert.

I believe it. That’s why you’ll never see me in a nursing home. I’ll be writing a book or inventing some new software program, but you will never catch me playing bingo in a retirement home.

Post 9

My mother totally believes in the decay theory. She is in her seventies, and she is doing all she can to preserve her memory of how to do certain things.

She is terrified of losing her mind with age, so she practices her favorite activities daily to keep from forgetting how to do them. She is a talented dressmaker and cross-stitcher, and she won't let her arthritis keep her from staying active in this area.

Also, she reads and does crossword puzzles often. She thinks that this keeps her memory from decaying, simply because she keeps her brain active.

It seems to be working. She still is able to talk about things that happened in our childhood, and we remember them, so we know that her memory is intact.

Post 8

@turkay1 – I think that when we forget things that should have been stored in our short term memory, often it is because our brains didn't label them as important enough to file away. Much like a document on our computer that we don't save before closing it because we don't deem it important, our brain prevents the occurrence from entering into our memory and taking up much needed space.

So, these forgotten events of the previous day are not really related to the decay theory at all, in my opinion. They are more related to our brain's filtering process, and it could be a sign of good brain function when the unimportant stuff gets cast out.

Post 7

@anamur – I'm sure that the decay theory describes this well. I took four semesters of Spanish in college, and now, I can barely remember how to say an entire sentence in that language.

However, I kept my old Spanish textbooks. When I read back over them, the words strike a chord in my mind. I do have those memories buried in my brain, and though they won't all come rushing back to me at once, I can coax a few of them to the surface by reading the old book.

Now, my college friend who took the same courses as I did uses the language every day. So, instead of losing her memory of the language, she has built upon the foundation and increased her ability.

Post 6

@truman12 – Journaling is a wonderful tool to help you preserve your memories. I have been keeping a journal since I was a teenager, and I am so glad that I have preserved memories that otherwise would have been lost.

Because of the journal entries, I can recall things that happened twenty years ago as I read about them. Without these descriptions of events, they would have faded away long ago.

I think it is interesting how a journal can guide my mind into recollection of something that would have disappeared from my memory long ago. Maybe a journal provides the pathway that the decay theory states that we lose over time.

Post 5

From what I understand the decay theory is entirely based on time. It says that after a memory is made, the more time that passes, the more difficult it becomes to retrieve that memory. But I'm sure that all of us have had an experience where we can remember something that happened ten years ago but we can't remember something from yesterday. How will the decay theory explain this?

I think that our brain and memory is very complex and there are many different factors that go into it. So the memory decay theory seems a bit too simplified in my opinion. We can't base on our ability to remember simply on time.

What do you think?

Post 4

@truman12-- I've heard that some vitamin deficiencies can lead to forgetfulness too.

I'm also horrible at remembering certain things, especially names, addresses and phone numbers. When I get a new phone number or address, it takes me months to remember it!

There was a doctor on TV who said that sometimes we forget things easily because we don't associate them with anything else. Apparently, instead of trying to remember something as is, if you try to associate it with something else, you will remember it better.

Post 3

Is the decay theory of forgetting also the reason why people forget languages if they never use them?

I hear people say this all the time. That they knew how to speak a language pretty well when they were younger but have forgotten due to lack of practice.

I never knew that when new memories are created, a new pathway forms in our brain. So I guess in order to remember what we've learned, we need to "use" memories so that the pathways become stronger and indestructible right?

Post 2

I have always suffered from forgetfulness. We all forget things but I am terrible about it. It goes beyond just losing my keys. For instance, I have no real memories from my late teen years. I can't remember much about my wedding day. I forget everyone's birthday. This can be a real problem in my life.

Looking for any kind of solution I began to do research on theories of forgetting. My research led me to decay theory. I read about one doctor who recommended that his patients engage in a kind of aggressive journaling process. They would spend up to an hour a day writing about the recent past and then reviewing past entries. By constantly recalling important events, people and places in their minds they were able to keep them from getting fogy in their memories.

Post 1

I think the clearest example of decay theory is the way that we remember our dreams. I will use myself as an example.

When I first wake up after a dream it is clear in my mind. I can remember characters faces, details about the setting, pieces of dialogue and every part of the plot. But If I don't write the dream down or make a conscious effort to review it in my brain it quickly begins to fade away.

Sometimes it is completely gone by the end of the day or the next mornings, so forgotten that it might as well have not happened. Is is like it is a victim of neglect and without the care and attention of your brain it will wither away and die.

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