The Decay of Memory

Decay Theory

Information in sensory memory and short-term memory decays quickly with time, but does long term memory decay as well? An early explanation for forgetting was Decay Theory, which proposed that as time passed and being disused, long-term physical memory traces in the nervous system can fade away. But Decay Theory soon fell into disfavour as scientists were unable to locate neither physical memory traces nor measure physical decay.

However, of recent decades, scientists have begun unravelling the manner in which neural circuits change with the formation of a long-term memory formation, sparking new interests in examining the way these changes might decay over time.

Unfortunately, Decay Theory’s prediction of; the longer the time interval of disuse between learning and recall, the less should be recalled; is problematic. For example, some professional actors tend to display perfect memory for words last used by them on stage two years ago despite having moved on to new acting roles and scripts.

Moreover, when research participants learn a list of words or a set of visual patterns and are retested at two different times, they, at times, recall material during the second resting that they were unable to remember during the first. This phenomenon, called Reminiscence, seems inconsistent with the concept that a memory trace decays over time. To sum up, scientists still debate the validity of Decay Theory.

Motivted Forgetting

Psychologists propose that people, at times, are consciously or unconsciously motivated to forget. According to Sigmund Freud, it was often observed that during therapy sessions, his patients remembered long-forgotten traumatic or anxiety-arousing events. For example, one of his patients suddenly remembered with great shame such an event in which she, while standing beside her sister's coffin, thought: "Now my brother-in-law is free to marry me."

Freud's conclusion was that the thought was so shocking and anxiety-arousing that the woman had repressed it and pushed it down into her unconscious mind, and left it there to remain until it was later uncovered during a therapy session. Repression is a motivational process which protects us by blocking the conscious recall of anxiety-arousing memories.

The concept of repression is controversial, with some evidence supporting it while others disreputing it. People do tend to forget unpleasant events—even traumatic events—yet they can forget very pleasant ones as well. If a person can't recall a negative experience, is it due to repression or to normal information processing failures? Overall, it has been difficult to demonstrate experimentally that a special process akin to repression is the cause of memory loss in the case of anxiety-arousing events.

Prospective Memory

Have you ever forgotten things like mailing a letter, turning off your oven, purchasing a thing you need from the market, or keeping an appointment? In contrast to Retrospective Memory, which is a reference to events of the past, Prospective Memory concerns remembering to perform an activity in the future. That individuals forget to do things as often as they do is interesting, because prospective memory typically involves little content.

Often we need only to recall that we must perform an event-based task ("Remember to mail the letter on your way home" or "Remember to buy milk when you are at the supermarket") or a time-based tasks ("Remember to take your medication at 5:00 pm" or "Remember to keep your doctors appointment at 2:00 pm").

Successful prospective memory, however, draws on cognitive abilities such as planning and allocation of attention while performing other tasks.

During adulthood, do we become increasingly absentminded about remembering to do things, as suggested by a common stereotype? Numerous laboratory experiments support this view. Typically, participants are asked to perform a task requiring their ongoing attention while trying to remember to signal the experimenter at certain time intervals or whenever specific events take place.

Older adults, in general, tend to display poorer prospective memory, especially when the signalling is time-based. However, when prospective memory is tested outside the laboratory using tasks such as simulated pill-taking, healthy adults in their 60s to 80s often perform as well as—or even better than—adults in their 20s. Perhaps older adults feel more motivated to remember in such situations, or maybe they rely more on habit and on setting up of a standard routine.

Amnesia

As  H.M.'s case illustrates, the most dramatic instances of forgetting occur in amnesia. The term Amnesia is commonly referred to as memory loss due to special circumstances such as brain injury, illness, or psychological trauma. However, as we'll see shortly, there is one type of amnesia experienced by everyone.

Amnesia takes several forms: Retrograde Amnesia represents memory loss for events that took place sometime before the onset of amnesia. For example, H.M.'s brain operation, which took place at age 27, caused him to experience mild memory loss for events in life that had occurred during the preceding year or two. For example, when he was 25 to 26 years old.

Football players experience retrograde amnesia when they are knocked out by a concussion; they regain consciousness and cannot remember the events that had occurred just before being hit.

Anteretrogade Amnesia refers to memory loss for events that occur after the initial onset of amnesia. H.M.'s brain operation and, pratricularly the removal of much of his hippocampus, produced severe anterograde amnesia, robbing him of the ability to consciously remember new experiences and facts.

Similarly, the woman whose hand was pinpricked by Swiss psychologist Edouard Claparède during a handshake also suffered from anterograde amnesia; moments later, she could not consciously remember the episode. But, unlike HM's anterograde amnesia, hers was caused by Korsakoff's Syndrome, which can result from chronic alcoholism. It may also cause retrograde amnesia.