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.