Healing Metaphysics Home > Archive> Memory's great disappearing act

The Weekend Australian
Copyright News Limited
Article by Greg Callaghan

It gives us our sense of identity and personal history: without it, we'd live in an eternal twilight zone of single moments. Small surprise that human memory is one of the mostly hotly investigated areas of neuroscience and pharmacology.

Try to picture it: a constant whirlwind of electrochemical processes that enables us to remember where we left our house keys, the first time we had sex, the automatic recall to drive a car, or simply to draw on useless memories such the banana skin we slipped on 20 years ago.

The old saying that memory fades with age doesn't hold up to recent research. The new scientific wisdom is that memory exists in multiple forms, involving many areas of the brain, most of which remain remarkably robust with age. As you get older, you aren't likely to lose your vocabulary, forget how to swim or ride a bike, for example. But even by your early 40's you may be suffering a slight decline in episodic memory, the type that deals with everyday events, such as the name of someone you have just been introduced to, or where you left your reading glasses.

As you approach 50, it might be harder to carry on a couple of conversations at once or absorb reams of new information easily. Recent studies have attributed this age-related decline in episodic recall to a degeneration of the frontal lobes, which may explain why very old people can remember events of 60 years ago, but may not remember what they had for breakfast.

On a brighter note, semantic memory, covering accumulated knowledge and wisdom, does not fade with age. Neither does implicit memory, which covers skills you practise automatically, such as riding a bike or speaking in sentences. Nevertheless, by the time you reach 65, you may have lost up to 20 per cent of your 100 billion brain cells and simple arithmetic shows this is going to have some effect on your recall. The decline in episodic memory may be partly ameliorated by regular physical and mental exercise (aerobic activities such as swimming and walking, and daily mental challenges such as the cryptic crossword).

When we challenge our brain we build new brain circuitry, even if we can't create extra neurons. Messages are transmitted from one neuron to the next across tiny gaps called synapses: these can be joined together by sticky molecules called alpha-integrin, which spread if a mind is stimulated (the message here is use it or lose it).

In the late 19th century, German psychologist Hermann Ebbinghaus developed a curve that represents how much we forget over a certain period. According to Ebbinghaus, 56 per cent of newly learned material disappears from our minds almost instantaneously. Another 10 per cent vanishes within a day and a month later nearly 80 per cent has gone.

This is because new material is constantly coming in to rewrite the old.

In the past five years, improvements in imaging technology have enabled neuroscientists to take pictures of the brain's circuitry with unprecedented precision. Powerful instruments such as magnetic resonance imaging and positron-emission tomography produce 3-D images that detect the chemical, electricity and blood-flow changes that occur in the brain when we laugh, talk, cry, eat or have an orgasm. MRI and PET have opened a window on serious mental illness such as schizophrenia, Alzheimer's disease and epilepsy.

US researches, for example, believe they have pinpointed faulty circuits in the frontal lobe that create the terrible voices and hallucinations of schizophrenia. It is believed schizophrenics may lack certain neurotransmitters that tell them something isn't real. Depression, which is two to three times more common in women than men, may be due to chemical changes in the brain triggered by environmental stresses to which women are more susceptible. MRI and PET help identify which parts of a brain have been damaged by a stroke and - by measuring scar tissue - can predict a person's ability to recover.

Each part of the body has its own headquarters in the brain. Functions and abilities tend to be highly localised, but memory tends to shift between different parts of the brain, depending on the need. The area that covers speaking (an ability that emerged about 150,000 years ago) tends to be focused in one hemisphere, while the zone controlling the man-made task of writing (10,000 years ago) is in another. Researches have mapped the place in the brain for perfect pitch in musicians. But a complete map of the human brain is still a long way off: scientists have drawn more than 30 maps for vision alone.

The brain's need for information categories may explain why people have little memory before the ago of four: an infant's world is too new to have a framework into which experience can be neatly filed. Although damage to certain areas of the brain, for example the hippocampus, affects memory dramatically, recent theories propose that memory results from the collective activity of billions of simple neural units. Damage to just a few of those units can result in particular memory blind spots.

Because of continuing breakthroughs in our knowledge of the brain - which absorbs 20 per cent of our glucose supplies - it is likely that within another generation we will see a whole generation of smart drugs emerging - to improve our memory, lift our mood and, more important, prevent the psychological carnage caused by Alzheimer's and Parkinson's diseases. Scientists are beginning to understand why some people become alcoholics or chain smokers or drug takers.

If you think many of these promises are overblown, consider this: your eyes do not see, your tongue does not taste, your fingertips do not feel: your brain does.

Healing Metaphysics Home > Archive> Memory's great disappearing act