Memory loss is something we all fear as we age. After all, memory is what makes us who and what we are, as having access to the huge database in our brain is integral to our very concept of ourselves. We can't survive independently without it. Performing even the simplest everyday tasks requires having a properly functioning memory. Without memory, we are little better than vegetables.
But is memory loss truly inevitable? If so, what can we do to prevent it, and how can we avoid it happening?
As WDDTY has discovered in this special report, losing your memory isn't necessarily a problem of the old. It can strike at any time of life, and be caused by stress, disease, the environment, drugs of all kinds and doctors. By addressing these underlying causes, it is possible to keep memory loss at bay.
The brain's capacity to remember remains one of the least understood areas of science. Basically, we know that the memory process occurs in three stages: encoding; storage; and retrieval. There are also two types of memory: short- and long-term. Our short-term memory is surprisingly limited - able to store an average of only seven items. However, the brain can increase storage capacity by 'chunking' the data into seven storage bins of related information - a bit like a computer. Long-term memory requires the information to be consolidated before it is stored, a process that remains poorly understood.
The bottom line is that there are many processes involved in memory, which makes it particularly vulnerable to breakdown by external factors.
Stress is the one we're most familiar with. We've all had the 'exam nerves' experience of forgetting something we know we can remember under ordinary circumstances. But it's an irritating short-term problem that is merely frustrating. Long-term stress is much more insidious. And this kind of stress has been found to be the cause of most permanent memory loss - a process that is now biochemically well understood. What happens is that the stress hormone cortisol attacks the hippocampus, the area of the brain intimately involved in memory storage, short-term memory in particular (Neuro Endocrinol Lett, 2002; 23: 199-208). The more severe the stress, the more significant the damage.
Brain scans of war veterans and victims of childhood abuse have shown dramatic objective evidence of damage to the hippocampus, primarily atrophy (shrinking) (Biol Psychiatry, 1999; 45: 797-805). Similar damage has been found in the brains of people suffering from long-term severe depression and post-traumatic stress (Arch Gen Psychiatry, 2000; 57: 925-35). It is also possible that cortisol-related neurodegeneration may predispose people to conditions such as Alzheimer's, where memory loss is completely disabling (Dev Psychopathol, 2001; 13: 491-513).
Besides stress and depression, there is also a number of more complex disorders affecting the brain that can cause havoc to memory - such as schizophrenia, obsessive-compulsive disorder, chronic fatigue syndrome, Huntington's and Parkinson's diseases, herpes of the brain, brain tumours, stroke and epilepsy.
However, there are physical conditions that initially appear to have little connection with brain function, but which can impair memory. Heart failure, for example, is a frequent culprit, probably due to the reduction of blood circulation in the brain (J Cardiovasc Nurs, 2003; 18: 219-42).
But the biggest offender is diabetes. There is growing evidence that diabetes can have drastic effects on memory, particularly short-term or 'episodic' memory (NeuroReport, 1997; 8: 1527-30). For reasons unknown, it appears to strike mostly older diabetics, although middle-aged people who don't have full-blown diabetes, but have glucose-regulation problems, can also be affected (PNAS, 2003; 100: 2019-22).
Indeed, diabetes seems almost to single out memory, as few other cognitive skills are affected (Diabetes Metab Res Rev, 2000; 16: 308-15). The fact that the maintenance of peripheral glucose levels would impact brain function is not surprising, given that the glucose borne by the blood accounts for 99 per cent of the brain energy requirements, says Dr Antonio Convit and his colleagues, from the Center for Brain Health at the New York University School of Medicine, but what is surprising is that the damage caused by hypoglycaemia [low blood glucose] seems to be restricted to the hippocampus - precisely the area involved in short-term memory (PNAS, 2003; 100: 2019-22).
Apart from glucose, low levels of hormones can also affect memory, particularly later in life. In about a quarter of women, the menopause will affect thyroid gland production of thyroxine, with catastrophic effects on mental processing. It's now known that even tiny deficits of thyroxine can adversely affect memory (Gynecol Endocrinol, 2003; 17: 79-85). There's also evidence that declining levels of sex hormones, too, can bring on memory loss - in both men and women (J Mol Neurosci, 2003; 20: 385-93).
Aside from the air we breathe, the most pervasive things in our environment are electromagnetic fields (EMFs). The whole of modern civilisation relies on electrical power, which bathes us all in its radiating fields. Some people are exceptionally sensitive to EMFs and suffer from a whole range of neurological problems, including memory loss (see WDDTY vol 16 no 1). Even more of us are affected by mobile-phone technology - in particular, mast transmissions - which have experimentally been confirmed to have detrimental effects on many cognitive abilities, including memory (see WDDTY vol 15 no 5).
The evidence that mobile phones themselves cause memory problems is more equivocal, as some studies show an effect, while others don't (Bioelectromagnetics, 2004; 25: 33-40; Bioelectromagnetics, 2005; 26: 102-8).
It's a clearer picture with environmental sensitivity in general - to foods or chemicals. The most common form of chemical sensitivity is 'sick-building syndrome', where out-gassing from such things as carpets, photocopiers and building materials can overload the immune system. Brain dysfunction is a common problem in chemical sensitivity, where we often see short-term memory loss, imbalance, dizziness and vertigo, says world authority Dr William Rae, of the Dallas Environmental Health Center. Food additives can be a particular problem, too, with substances like MSG (monosodium glutamate) and aspartame causing a variety of cognitive problems (Blaylock RL. Excitotoxins: The Taste That Kills. Santa Fe: Health Press, 1997).
Pesticides are another important cause of memory problems, although fairly high doses are needed to produce serious adverse effects on memory - for example, among farmers exposed to sheep-dip. Pregnant mothers need to take extra care, as their unborn young are very susceptible to pesticides, leading to short-term memory problems as the child gets older (Nutr Health, 1992; 8: 33-43).
Drugs of all kinds
For years, the tabloid press have been banging on about how illegal drugs can 'fry your brains', but without much scientific evidence behind it. However, recently, worrying data have surfaced for some common recreational drugs. Heavy users of cannabis, for example, have been found to have cognitive deficits, including memory loss. Fortunately, however, no memory problems have shown up among people who smoke less than a joint a day (Psychopharmacology [Berl], 1993; 110: 219-28).
Long-term users of ecstasy (MDMA, or methylenedioxymethamphetamine) may also develop problems specifically with memory, while leaving other cognitive processes relatively unaffected, says Dr Phil McGuire of London's Institute of Psychiatry (Toxicol Lett, 2000; 112-113: 153-6). More worryingly, the memory damage seen in long-term MDMA users appears to continue even after stopping the drug (Pharmacol Biochem Behav, 2002; 71: 837-44).
Alcohol, too, has major effects on memory. Most of us - either personally or vicariously - are familiar with memory 'blackouts' caused by serious alcohol overindulgence. These are usually laughed off, but there are major insidious consequences - especially for adolescents, according to a recent study. Alcohol affects behaviour and brain function differently in adolescents and adults, say doctors at Duke University's Department of Psychiatry. The functioning of the hippocampus is uniquely responsive to alcohol during adolescent development, and may be more susceptible to alcohol's neurotoxic effects (Ann NY Acad Sci, 2004; 1021: 206-20).
That difference between adults and adolescents is underscored by an eight-year Dutch study, which found that mild to moderate alcohol consumption (one to four drinks every day) actually reduces an adult's risk of developing severe memory loss (Lancet, 2002; 359: 281-6).
Problems with recreational drugs are dwarfed by those caused by legally prescribed doctors' drugs - in fact, even by the drugs you can buy without a prescription over the counter (OTC).
Take statins. These anticholesterol drugs are among the most widely used medications in the world, particularly now that they can be bought OTC. They have achieved their OTC status because governments around the world have been convinced that the drugs are harmless. Recently, however, some statin users are beginning to report memory problems. One dramatic case is that of astronaut Duane Graveline, himself a medical doctor. His statin nightmare started a few days after taking just 10 mg/day of Lipitor. My wife noticed me walking aimlessly about the yard after my return from my usual walk, he says. I did not know who she was and would not enter our house. He immediately stopped taking the drug, but was persuaded to start again after his own doctors convinced him that statins were safe. Reluctantly, he resumed, this time taking just 5 mg/day. Six weeks later, I descended again into the black pit of amnesia, he reported. Gone from my memory was my medical-school training, USAF flight-surgeon career, my marriage and four children, and even my selection as scientist astronaut.
Although in a minority, more and more patients are finding their memory affected by statins, a serious side-effect that is currently inexplicable (Pharmacotherapy, 2003; 23: 871-80).
More common, and explicable, are the side-effects of tranquillisers, long known to cause muddled thinking - and memory loss (Vertex, 2001; 12: 272-5). Antidepressant drugs can do the same (Ann Clin Psychiatry, 2004; 16: 15-25).
Indeed, memory loss is one of the most common side-effects of a whole range of pharmaceutical drugs (see upper box, p 3).
A number of medical procedures can also affect memory, the most celebrated of which is electroconvulsive therapy (ECT) for depression. Short-term memory loss is common after ECT, and can be as disabling as the original depression (Depress Anxiety, 2000; 12: 130-4).
Heart bypass surgery often has major cerebral consequences. Staggeringly, over half of these patients develop cognitive decline as a direct result of the operation. It's mainly confined to short-term memory, but can persist for as long as five years (N Engl J Med, 2001; 344: 395-402). It is thought that bypass surgery causes microscopic blood clots in the brain (Stroke, 2000, 31: 707-13).
Radiation therapy to the brain also has an impact on memory (Curr Opin Neurol, 2003; 16: 129-34). Less easy to explain is the memory loss caused by a diagnostic procedure as routine as magnetic resonance imaging (MRI), yet four separate studies have found it in a significant number of patients (J Magn Res Imag, 1992; 2: 721-8).
Whatever the cause, memory loss must surely rank among the top-10 of terrifying life events. As astronaut Graveline puts it, This is not a complaint to be buried with constipation and insomnia as just another drug side-effect. Memory is the essence of what we are. And to be deprived of memory can place one in harm's way; one's very life or the lives of others may be at risk.