The findings were aired in a BBC documentary which investigated the science behind people's personalities and whether it was possible to change them.
Viewers watched as presenter Michael Mosley, who has suffered with chronic insomnia for the past 20 years, explained how he wanted to become a "warmer, happier person and to sleep better".
The father-of-four had his brain tested at Essex University by Professor Elaine Fox, a leading researcher into the science of optimism.
The results showed he had more activity in parts of brain associated with negativity, pessimism and a strong tendency to look on the dark side of life.
Past studies have found people who are prone to high levels of pessimism, neuroticism and anxiety suffer from cerebral asymmetry, where there is greater activity on the right side of their brain than the left. The cause of this is not yet known.
By analysing electrical activity in the brain, experts were able to show that the right side of Mr Mosley's brain was three times more active than the left when in its resting state.
Professor Fox suggested Mr Mosley should undertake two forms of mental training daily.
The meditation excercise involved sitting in a quiet place and focusing on physical sensations, such as the weight of his body or breathing, for 20 minutes.
He met a former monk who told him about the ancient art of mindfulness, a form of meditation. The monk said said that everyone could benefit from taking ten to 20 minutes out of each day to cut off from the outside world and live in the moment.
The trick was to start doing this exercise for ten minutes, then build up to 20 minutes each time.
Eventually the technique enables the person to let their thoughts come and go freely without ruminating on them.
The second exercise involved looking at a screen showing 15 blank or angry faces, and one smiley face.
Mr Mosley had to spot the smiling face and click on it. A new set of faces then appeared.
The idea behind the excerise was to train his brain to look for positive images. By regularly doing this, it is thought the brain learns to tune into positive thoughts more easily.
After seven weeks, Mr Mosley felt his mood lifting, he started sleeping better and felt more optimistic. He then returned to the lab to see if his brain had in fact changed.
Mr Mosley was told the asymmetrical levels of his brain activity had become more equalised - a strong indicator he had become more optimistic.
In addition to this, his scores when reacting to the brain training game had changed. He reacted more quickly to happy faces and more slowly to sad faces, indicating he was not seeking out negativity as much.
Dr Mosley told BBC2 programme, Horizon: The Truth about Personality: "I feel quite frankly astonished that you can notice that much change in just seven weeks. I set out to see if it was possible to change my mind and I think I might have done it. I am absolutely thrilled."
LOOK ON THE BRIGHT SIDE: THE NINE RULES FOR BECOMING AN OPTIMIST
Mindfulness, a form or meditation, is an ancient practice that involves focussing a person's awareness and attention but at the same time maintaining a sense of calmness and relaxation.
Try working this exercise into your routine each day for 10 minutes and slowly build up to 20 if you want to try and change your mindset.
• Before directing your mind towards the anxiety or negative thought you are experiencing, focus on your breathing - the sensation of air slowly flowing into your nostrils, streaming down the back of your throat and into your lungs.
• Feel the beating of your heart and imagine how it pumps oxygenated blood around your body. Continue until you're ready to meditate.
• Now, shift your attention to your anxious thoughts. What thoughts are present in your mind right now? Are there many moving quickly or does each one remain for a while? Consider the thoughts objectively rather than reacting to them emotionally.
• There's a myth that when you meditate, you should have a blank mind. But thoughts are not the enemy and trying to stop them will only lead to more struggle.
• Treat the thoughts during meditation like having a radio on in the background - you can hear it, but your main focus is elsewhere. In mindfulness, you're paying attention to the fact that you have a thought but you are not buying into what it is saying.
• Try not to judge the thought as 'good' or 'bad'. Cultivate an attitude of equanimity to whatever goes through your mind. Watch your thoughts with curiosity and kindness and they will become easier to bear.
• Whenever you notice your mind is wandering, acknowledge that it has meandered and gently bring your attention back to observing your thoughts.
• Continue working with your worries in this way for the period of time you have chosen. Working mindfully can be challenging, so it's good to practise for short periods at first.
• You may feel dizzy when you start but that's because you've suddenly stopped spinning around in circles. In the stillness of meditation, it can also seem as if you have more thoughts than usual but this is not so: it is just that you are becoming more aware of them. The more you practise, the more your mind can deal with worries in a less panicked way.
The Mindful Manifesto, by Dr Jonty Heaversedge and Ed Halliwell, Hay House, £10.99 (NZ$21.07).
Are you an optimist or a pessimist? Take Professor Elaine Fox's optimism test.
- Daily Mail
