The challenge for scientists is to discover whether or not there are any neurological differences between the brains of people who appear naturally happy, and those of people who, although not clinically depressed, would certainly not describe themselves as happy, or might claim to feel so only fleetingly. (Many of us probably fall into this category.) And if an unhappy person can be transformed into a more joyful one - which is where the psychologists come in - will this change of state be reflected in their brains?
Caroline Ponting, 55, from Harrogate, Yorkshire, is one of three unhappy people who took part in an experiment devised by QED, the BBC television programme, to see if they could acquire and maintain happiness, and in so doing answer some of the scientific questions relating to this sought- after condition.
Ponting was the most unhappy of the volunteers, a rather fierce and frank- spoken divorcee who had given up a much-loved job as a greeter at a local restaurant, to care for her mother who had been severely disabled by a stroke. At the start of QED's two-month training course in happiness, her resentment and bitterness on how her life had turned out was startling, and her lack of feeling for her 92-year-old mother a baldly stated fact. "She's been with me not out of affection but out of duty," she said. "I don't feel love for her ... I couldn't cuddle her."
Ponting saw her life as a trap. She felt that she could not communicate and that what she had to offer or say to others was of no interest or value. "My life had been full of sparkle. It was like a glitter-ball on a dancefloor. When my mother came to live with me it became tarnished. It stood still."
Her greatest wish was to feel a "part of life and everyday people again".
Questionnaires based on the Oxford Happiness Inventory and the University of Otago affectometer - accepted psychological tools for assessing state of mind - confirmed that Caroline Ponting was a deeply unhappy woman. She scored minus 40.
Harder scientific evidence was provided by a scan to determine the happiness levels in her brain. Professor Richard Davidson and his team at Madison University have located the "pleasure" zone of the brain - where happiness appears to be registered - in the left pre-frontal lobe (or the area just over the left eyebrow, and vice versa for left-handed people), by showing volunteers hundreds of photographs, ranging from smiling babies to war casualties, designed to trigger a variety of emotions. Using a perforated shower-cap device attached to some electrodes for monitoring brainwaves, Davidson has discovered that in naturally happy people there is a high rate of activity in the pleasure zone, even in the resting or emotionally neutral state.
These people - the "Pollyannas" of this world - are primed for happiness, and their pleasure zone is fired at the first hint of it. The pleasure zone is markedly less active in the "Jeremiahs", and by comparing Ponting's brain scan with a database of scans of thousands of cheerful and miserable people, Davidson saw clearly that she fitted into this category.
She was then handed over to Robert Holden, a relentlessly up-beat and positive psychologist ( "When I started in this, people assumed I was American"), who founded the first NHS laughter clinic, and is undoubtedly a happiness expert. There are, he says, no great secrets to achieving happiness, it is largely common sense. "But finding happiness is a bit like the famous Monty Python sketch, 'The 100 metres dash for people with a poor sense of direction', which had all the competitors milling around in different directions. We are all living very fast lives. Very busy achieving a lot. Being busy doesn't mean being happy. In fact, we are so caught up in our lives that we don't ask ourselves often enough if we are happy, we're just aware that we are not."
We attempt to justify this, Holden says, by placing our ultimate attainment of happiness somewhere in the future. "People are waiting to be happy. Today is for quiet desperation, and happiness is just around the corner. But happiness is a journey not a destination."
Under Holden's guidance, the QED guinea pigs seeking to change their misery into merriment first attended one of his workshops where the emphasis was on their fears about happiness - the guilt it might generate, the disappointment if it did not prove to be enough - and their erroneous belief that it had to be earned, to be paid for in some way. They were invited to share with each other what they enjoyed about life, and to relate a recent feel-good experience.
Having primed Ponting and the other volunteers to think more positively, Holden told them to stick blue dots in highly visible places such as on a mirror, a car petrol gauge or a fridge, to remind them to think positive thoughts.
In addition, they were to spend 30 minutes a day doing some form of aerobic exercise. This generates a rush of endorphins, the body's naturally occurring opiates which are associated with a high. Professor Michael Argyle, a psychiatrist at Oxford Brooks University and an advocate of Scottish dancing as a route to happiness, says that more doctors are prescribing exercise rather than drugs for mildly depressed patients. "Some studies show that exercise is as effective as psychotherapy," he says. "In one study, a brisk 10-minute walk had measurable effects on the state of mind of patients two hours later."
Learning to laugh and smile was an essential component of the course. According to Professor Davidson, even a smile can help to shift the brain into a happier state. "But it must be the right kind of smile. A social smile when the cheeks are just pulling the mouth up does not produce the same effect on brainwaves as a voluntary smile using the cheek and eye muscles." British research shows that people who are naturally happy are those who have clearly defined "achievable" goals, and extroverts who assume that everything will go right and who do not dwell on things that go wrong.
The guinea pigs, all of whom at this stage of the experiment were already measurably happier than at the start, were asked to draw up a five-year plan, a six-month plan and a one-month plan for their lives. The important thing was not to be too ambitious, which would have posed the risk of confirming their own worst fears about themselves - that they really were failures. Dawn Harrison, a thirtysomething private detective and mother of three from Devon - whose twinkly, happy demeanour belied a devastatingly low sense of self-esteem - found this the most beneficial part of the course. She started with little lists of daily tasks which, when completed, gave her a real sense of achievement.
Dr Richard Depue, of Cornell University, another prominent figure in the scientific search for happiness, says there is a link between achieving goals and being happy. "There are two kinds of happiness: 'incentive happiness' and 'gratified happiness'. We get a good feeling when we know we can attain our goal, when we can see an end in sight. There is a very powerful sense of enthusiasm, optimism and power. This is associated with a release of dopamine, a brain chemical. Drugs like coke and amphetamine create this same feeling." Gratified happiness or gratification euphoria - when goals have been reached, when they can be ticked off that list - is due to a rush of endorphins.
Keith Allan, 41, from Weston-Super-Mare, Somerset, the happiest of the unhappy volunteers, according to the questionnaires, and someone who had made radical life-style changes in his search for happiness, actually found this part of the course the hardest. He resented what he saw as the regimented goal-setting which harked back to his successful and well- paid career as a salesman. He had given it up because he saw it as a factor in his feeling that he appeared to have everything but it wasn't enough.
The final ingredients in the QED recipe for happiness were a good night's sleep, half an hour a day spent doing something the guinea pigs really enjoyed, and a treat or two. A happy person will sleep better, and the person who sleeps better is more likely to have happiness, the theory goes.
Caroline Ponting's discovery of beadwork jewellery-making and Keith's new hobby of fishing reinforce their newly awakened sense of well-being. And the treats encourage them to like themselves, says Robert Holden. "If you don't like yourself, you will never be happy - alone or with other people."
At the end of the course, all three guinea pigs were far happier than they had been at the start, as their questionnaire scores proved. But the best evidence that the Jeremiahs can be transformed into Pollyannas was provided by Ponting's final brain scan. The trace had shifted so dramatically that it was now off the scale. "Her brain pattern indicated she was one of the happiest people I had ever seen," Davidson says. Well, not quite. The only person who had scored higher had been a Tibetan monk.
More than six months after the course, Ponting is adamant that she is now a happy person. "Nothing in my life has really changed ... so the happiness I feel must be coming from within."
'How To Be Happy' is on BBC 1 on Wednesday at 10pm.