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.

The Psychology of Hunger

Eating and digestion supply the body with the necessary fuel needed for function and survival. Metabolism is the body's rate of energy (or calorie) utilization and several psychological mechanisms that keep our body in energy homeostasis by regulating the food consumption rate. For example, some psychological signals induce hunger and prompt the need to eat, while others stop the intake of food by producing satiety (the state in which we don't feel hunger anymore).

However, this is not the case as many people believe that hunger and eating simply occur when energy levels in our bodies run low and that we feel full when our immediate energy levels are restored. Our body monitors its energy supplies, but this information interacts with other factors; for example, the amount and variety of food to regulate the food intake—making hunger and satiety not necessarily linked to immediate energy requirements. Moreover, homeostatic mechanisms are designed to prevent us from running low on energy in the first place. In evolutionary terms, an organism that did not eat until its energy supply started to become low (in any absolute sense) would be at a serious survival disadvantage.

Finally, many researchers believe that there is a set point; or, as said biologically, a determined standard; around which body weight (or more accurately, fat mass) is regulated. This view holds that if we tend to overeat or undereat, homeostatic mechanisms alter our energy utilization and hunger to make us return to close to our original weight. But some researchers argue that the set point theory has limitations. They propose that as we overeat or undereat, homeostatic mechanisms make it harder to keep gaining or losing weight, but do not return us to our original weight. This makes us possibly settle in a new weight over time. Stated in a different point of view, "Biology does not determine a fixed body weight but rather, a range or zone of body weight."

Genes and Environment

Some individuals gain weight more easily than others even with less consumption of foods as well as  less fatty food consumption, while there are others who eat in excess with more fatty food and still stay slim for example: South Esat Asians who eat an excessive amount of fat still stay slim while others can gain weight with less amount of fat consumption. The reason for this can be in the genes, making some individuals more susceptible to gaining weight due to low metabolism, while others stay slim due to high metabolism. But there can be hormonal factors which contribute to weight gain and loss as well; such as thyroid conditions, thyroid dominance and menopause in some people. Heredity influences one's basal metabolic rate, causing a tendency to store energy as fat or lean tissue. Identical twins that are raised apart are about as similar body mass as identical twins who are raised together. This makes the genetic factors account for about 40% to 70% of the variation in BMI among both genders.

According to studies, over 200 genes have said to be have been identified as possible contributors to human obesity. However, although heredity affects our susceptibility to obesity, the environment does play a part in causing obesity too. There haven't been much changes in genes in recent decades, but the rate of obesity has had a significant increase. Experts believe the reasons to be the abundance of inexpensive foods that taste good but contain a high percentage of fats and carbs; a cultural emphasis on getting the best value, which contributes to the supersizing of menu items; and the advances in technology, which decrease the need for daily physical activity.

The Pima Indians of Arizona have provided a striking example of the way genes and environment interact in producing obesity. The Pimas have a genetic predisposition to obesity and diabetes, but before the 20th century, both these conditions were rare among the members of the tribe. Their native diet and the physically-active lifestyle prevented their genetic predisposition from expressing itself. But Pimas born after World War II, in particular, have had a dramatic increase rate in obesity with the adoption of a westernized diet and sedentary lifestyle. Today, the Pimas living in Arizona have one of the highest rates of obesity and diabetes in the world. In contrast to this, however, the Pimas living in northwest Mexico have a much lower obesity rate than their Arizona counterparts due to their sticking to a more traditional diet with more performance of physical labour.

Dieting and Weight Loss

However, for millions of overweight people, being fat primes them to stay fat, in part by altering their body chemistry and energy expenditure levels. This is an example of why obese people generally have high levels of insulin (a hormone that is secreted by the pancreas helping convert glucose into fat) than people with normal weight do. Substantial weight gain can also make it hard to exercise vigorously, and dieting slows the basal metabolism as the body responds to food deprivation with a decrease in energy expenditure.

Does this mean that diets are doomed to fail? The common adage of "Ninety-five percent of individuals who lose weight, regain the lost weight within a few years" evolved from a single study that was done decades ago. According to Albert Stunkard, one of the researchers, 100 obesity patients were given a diet and sent off, which was 'state-of-the-art' in 1959. There are no good longterm estimates of weight loss success rates in part because we rarely hear from people who succeed (or fail) on their own without the help from clinics or treatment programmes.

There are reports of around one-third of Americans trying to lose weight, although not all of them are the ones who necessarily need to lose weight. There are significant sex and ethnic differences in dieting emerging from adolescence. Some dieters are motivated by health consequences, while the primary motivators to be slim are psychological concerns and social pressures—especially among women. Which may begin as a diet may, unfortunately, evolve into a life-threatening eating disorder.

Eating Disorders: Anorexia and Bulimia

According to researchers, the motivation of abnormal behaviour (like seen in anorexia and bulimia) could be caused by the contribution of psychological, environmental, and biological factors. Researchers are unable to experiment on individuals affected by these disorders in order to manipulate possible causes to check if individuals become anorexic or bulimic, but they are able to examine the factors associated with the disorders, as well as the changes that occur in the individuals when they are treated successfully.

Risk Factors

Two college freshmen named Sara and Lisa suffered from eating disorders. Sara was a victim of anorexia nervosa, which was an intense fear of being fat, causing her to severely restrict her food intake to the point of self-starvation. Despite looking emaciated and weighing 85 percent less than a person would be expected to be according to the said person's age and height, anorexic patients continue to view themselves as being fat. Anorexia causes a cease in menstruation, produces bone loss, stresses the heart, and increases risk of death.

Individuals like Lisa, who suffers from bulimia nervosa, are also in fear of getting fat. They tend to binge-eat, after which they purge the food by inducing vomiting or using laxatives. Often individuals suffering from bulimia consume between 2,000 to 4,000 calories during their binges. In some cases, they tend to consume around 20,000 calories per day. Although most bulimics are of normal body weight, repeated purging can cause severe physical consequences; which include gastric problems and badly-eroded teeth. Whereas most anorexics do not see their food restriction as problematic, bulimics typically do. However, they find it extremely difficult to alter their binge-purge pattern.

According to Becker, in 1999, around 90 percent of anorexic and bulimic individuals were women. According to some surveys, up to 10 percent of college women exhibited symptoms of bulimia although the general prevalence among North American women was 1 to 3 percent compared with 0.5 percent for anorexia. The latest statistics will be higher.

Sociocultural Factors

Anorexia and bulimia are more common in industrialized cultures, where being thin is equated to beauty. However, cultural norms alone cannot be held accountable for eating disorders as only a small percentage of women within a particular culture tend to be anorexic or bulimic; personality factors can be part of the issue. Anorexic individuals are often perfectionists. For example; Sara, who was a high-achiever (a highschool valedictorian), strove to live up to lofty self-standards which included strict ideals of an acceptably thin body. For Sara and Lisa, losing weight became a battle for success and control.

Their upbringing too may have played a role in their need for perfectionism and control. According to their description of their parents; they are disapproving, with expectations of abnormally-high achievement standards. For some anorexic children and teens, food refusal may be reinforced by the distress they cause their parents to feel; making self-starvation a way to punish their parents while gaining some control over their lives. As one anorexic patient said in a therapy session: it was like a power thing; I was showing my mother that  I don't need to eat and I can make her mad. The last thing a  parent wants is for you to die. You can get back at anyone, but if I  need to find a way, I had to forgive her as I am killing myself.

For individuals with bulimia, a different pattern from anorexia emerges; tending to be depressed and anxious, with an exhibition of low-impulse control, as well as lacking a stable sense of personal identity. Their food cravings are often caused by stress and negative mood, causing them to binge-eat to temporarily reduce their negative emotional state; followed by feelings of guilt, self-contempt, and anxiety—which is followed by the purging, maybe as a means of reducing these negative feelings.

Genetic Factors

On the biological side, genetic factors appear to predispose some individuals towards eating disorders. The concordance rate of eating disorders is higher among identical twins than among fraternal twins. The concordance rate between first-degree relatives, such as parents and siblings, are also higher than third and fourth-degree relatives. Researchers are searching for specific genes and combination genes that could be contributors to eating disorders.

Anorexia and bulimia exhibit abnormal activity in serotonin, leptin, and other body chemicals. According to the belief of some researchers, neurotransmitter and hormonal imbalances help in the causing of eating disorders; but others propose that the abnormal eating patterns are the initial cause of the chemical changes as a response that, once started, perpetuate eating and digestive irregularities. Other bodily changes also help in the perpetuating of eating disorders. An example of this is the stomach acid which is expelled into the mouth during vomiting, which causes those suffering from bulimia to lose taste sensitivity and also makes the usually unpleasant taste of vomit more tolerable.

Treating eating disorders can be difficult, taking years; but with professional help, around half of all anorexic and bulimic patients are able to make a full recovery while others are able to eat more normally while still maintaining their preoccupation with food and weight.