A surprising amount of research has been conducted in this area. Dr Barbara Pickard of the University of Dundee has been looking at the physiology of pleasure, while in Australia Dr Robert McBride has focused more narrowly on "the psychophysics of taste". Professor David Warburton, director of human psychopharmacology at the University of Reading, has been sufficiently interested in the findings of pleasure researchers round the world to found Arise (Associates for Research Into the Science of Enjoyment), with the aim of co-ordinating research and keeping its 50 or so members informed about one another's work.
Most are agreed that pleasure, far from being a nebulous emotion, has its own neurochemistry which can be traced to distinct areas of the nervous system. The so-called "pleasure pathway", Professor Warburton explains, passes through the most primitive part of the brain, the brainstem, and is observable in other animals as well as humans.
"The process is easier to monitor in rats. It has been shown that, when their taste receptors are stimulated with sugar, there is a greater activation of nerve pulses along this pathway. This knowledge has benefited humans, too. Patients in the critical stages of cancer, where the pain is too great to control, may be given the option of having electrodes mounted in their skull to stimulate certain areas of the brain."
When people are happy and experiencing pleasure, the body's defence system can be proven, through blood and saliva tests, to be high. When they are unhappy, stressed or depressed, these levels are measurably lower, leaving them much more open to infection.
Happiness is also associated with longevity, as was proven in a long- term study (by Winokur and Tsuang) reported in the American Journal of Psychiatry in 1975. At the end of the 30-year trial period, two-thirds of the "depressed" group in the survey had died (8 per cent were suicides) whereas only one third of the control group had, and none of them from suicide.
Pleasure is undoubtedly good for you, but what if it takes the form of substances - such as cigarettes, alcohol, chocolate and fatty foods - that are thought to be harmful? Are even forbidden pleasures better than none at all, and why are they so pleasurable anyway?
Caffeine and nicotine, Warburton explains, "elevate mood by acting on the dopamine pathway in the brain" (dopamine is the neurotransmitter found to be essential for stimulating the "brain reward" mechanism seen in rats). They also appeal to us because they have enhancing effects on performance and productivity.
"There seems to be an absolute improvement in work output as a result of caffeine," Warburton says. "Nicotine produces an absolute improvement in information processing, attention and memory. Alcohol, though, may impair performance but produces relaxation and can be seen as an escape from problems."
Chocolate - craved by so many - is not just the ideal combination of sweetness and creamy, mouth-watering texture, but contains theobromine, a potentially "psychoactive" stimulant of the central nervous system. However, it does have its drawbacks. The glucose in chocolate triggers an increase in the production of endorphins - the body's natural opiates - which in turn can lead to a cycle of craving.
One interesting conclusion from Arise's research is that even consumption of such "forbidden fruits" can be beneficial, as long as it is unaccompanied by guilt, which produces as many negative physiological reactions as pleasure does positive ones. The worst combination is to indulge, then feel anxious about it. "Guilt is basically stress," warns Professor Warburton, "and can be measured using a lie detector. The heart beats faster, the blood pressure rises, the palms sweat, the blood vessels dilate causing flushing. The stress hormone cortisol increases with the level of guilt, cholesterol rises and immunoglobin A - which protects against upper respiratory infections - drops. There are fewer lymphocytes and natural killer cells to fight off infections."
But isn't there a danger in Arise's suggestion that indulgence without guilt is good for you? Professor Warburton is quick to point out that he and his colleagues aren't advocating orgies of over-indulgence. "Pleasure in moderation is the key, so you can enjoy the things you like without guilt. I'm going to drink better wines from now on, not more wine."
Despite Arise's research, the measurement of pleasure and what triggers it remains complicated. Activities which seem pleasurable and de-stressing can turn out to be the opposite.
"With cigarette smoking," says stress consultant Dr Malcolm Carruthers, "people may feel calmer but their systems are under increasing stress. This is known as Nesbit's Paradox. The same can be true of coffee and rich foods."
Dr Carruthers, who teaches stress management techniques, believes we would be better off educating ourselves to appreciate more genuinely fulfilling pleasures. "The Yogic philosophy is that true pleasure lies within," he says. "Pleasure is peace of mind. There are many paths to pleasure, and chocolate and coffee - which I don't decry - are merely shortcuts."
Neil Sherwood of Reading University, a member of Arise, disagrees: "One study showed that the effect of a daily bottle of beer on 34 senile patients was dramatic," he says. "Compared with a control group on orange juice, they were measurably less morose and distant and much more talkative and alert."
Research has also proved conclusively that laughter is good for you. The International Journal of Humour Research, dedicated to promoting this theory, recently published a study by Dr William Fry, a lecturer at the Stanford University School of Medicine in California. It demonstrated that laughter boosted the cardiovascular, respiratory, muscular, hormonal, central nervous and immune systems - not least by drawing more oxygen into the lungs. "A child of six laughs 300 times a day," Professor Warburton concludes, "while the average for an adult is 50 and for a depressed person less than six. The physical act of smiling can produce measurably lower levels of stress hormones." !
In a 1993 poll conducted by MORI for Arise (the Associates for Research Into the Science of Enjoyment), these were the top 13 sources of pleasure cited by participants in the UK. The results were part of a survey of 1,509 people in the UK, Germany, France, Spain and Italy. They perhaps demonstrate the problems of getting people to talk without inhibition about pleasure, particularly in telephone interviews or within the framework of multiple choice questions.
1 Drinking tea and coffee
2 Reading books or magazines
4 Watching television
5 Family and children
6 Entertaining friends
7 Listening to the radio
8 Going out for a meal
9 Shopping/spending money
10 Having people round or going to their
houses for tea and coffee
11 Going out for a drink with friends or family
12 Having a drink of alcohol