the word stimulation derives from the word stimulus. The latter comes from an original Latin root, for which one dictionary offers a number of interesting early translations, including ''a goad used for driving cattle or slaves'' and ''a pointed stake to repel the advance of enemy soldiers''. In the sense that stimulation does provoke original thinking and can overcome boredom, there is still a connection to its modern meaning.

Stimulation is actually great. But doing is often far better than passively watching from the sidelines of life. The experience of creation is one of the essential motivations for the actively involved. The product of the creative effort, or of recreational thrills and fun, is not necessarily the main goal. Something too easily achieved is as boring as yesterday's stale news.

Challenge is also necessary - an experience is optimal when the person has enough skill to carry it out satisfactorily and to progress in meaningful phases. The particular game or brain exercise used to do this should be difficult enough for the participant to feel the risks of success or failure, balanced a little precariously on the edge of the possible.

Stimulation of the mind automatically will focus more attention on to novel targets. Stimulation on its own can powerfully reinforce further exploration. Arousal levels and attention improve apace. For instance, by using techniques based on these principles, even patients with partial amnesia can be helped and guided to improve their memory's functioning. One way this is done is to provide a novel visual experience to accompany each of their victories in remembering.

During the active reception phase of stimulation there are a number of significant events in the brain. These are best understood as results of the stimulation, and not something coincidentally going on. For instance, there are improvements in the amount of blood flow to the brain areas that are being used.

There are also increases in the chemical turnover and electrical activity of the brain cells in the same areas, and in related areas along connected pathways. Stimulation produces a release of amino acids that act as transmitters of messages to the relevant areas. It is believed that, in healthy people, especially children, such stimulation forces some cells to branch out: these new branches, or dendrites, connect with nearby branches, or grow, and are thereby able to hold more information within them.

The brain itself has among many of its primary functions the programming, regulating and verifying of this mostly semi-conscious activity. It checks itself to see how what it takes in accords with what is going on in its environment. Much of these control operations are under the direct control of the frontal lobes, Impulses in these are charged, depending on how much stimulation is needed to understand and interpret whatever is coming to them from outside. A constant flow of impulses from these frontal zones hurtle throughout the deeper, more primitive parts of the brain, playing an essential role in regulating how alert and attentively focussed the brain is generally.

Not enough stimulation can be detrimental; too much stressful stimulation can also have quite dramatic adverse effects. Janice Kiecolt-Glaser, a clinical psychologist at Ohio State University, has been involved in testing mind-body connections on students during their final year examinations. She observed a significant decline in the number and activity of certain cells of the immune response system, such as natural killer cells and T-helper lymphocytes, during this stressful period. The implication of this is that a holistic balance of stimulation is best.

Coping strategies for avoiding stress from too much stimulation: the three Cs of active involvement and participation - Commitment, Control and Challenge - have been said to act as buffers against stress. There are other coping strategies that can have the same ultimate beneficial effect. One is anger control. This does not mean ''bottling up'' gripes and bad feelings; it centres on expressing, as tactfully as possible, whatever is bugging you as near the time it happens as possible. This is one reason why assertiveness training is used to help anxious people manage social skills more fluently.

Harbouring a sense of injustice without letting it out sours many a relationship and person. Different forms of relaxation and/or meditation are always helpfully important here, and engaged in for several brief periods each day they can even be protective. For instance, such techniques have been shown to be fully capable of gradually lowering blood pressure, effectively by up to about 15%, and this works in synergy with any required medication.

My work in a large general practice showed such an approach to be practicable for those who felt able to devote only about 30 minutes of their time to such positive self-help endeavours. Relaxation therapy would not be expected to cure the underlying problem in its own right, but it does allow the individual some time and breathing space to re-assess their thinking and behaviour in a state of relative tranquillity.

The last of the coping strategies is self-determination. This refers to more than feeling or being in control. It means the ability to initiate whatever you want to do on your own terms. This is a goal many people in the midst of their life crises yearn for. A person should be able to exercise their unique combination of ideals, skills and qualities to fulfil what they see their life's purpose to be. That is the essence of what he or she may really want. It may be these coping strategies are some of the ways healthy optimists positively effect their heart and circulatory systems and, to a lesser degree, their immune response systems. As stress and illness are so intertwined, the reverse seems to be the case.

l Dr David Weeks is a clinical neuropsychologist and co-author of Superyoung (published by Hodder and Stoughton at #9.99).