AT THE age of 72, avid mahjong player Madam Ng Kum Leong can still sit 36 hours at the table - keeping track of her tiles.

She says she easily stays alert through the first 20 hours, winning most hands.

After that, she admits to making less considered moves.

'Even when my hand is not favourable, I'll still hang on, increasing the stakes, hoping to win big,' she said, laughing.

Instead, she invariably loses - everything.

Madam Ng is typical of many who make rash decisions when exhausted and deprived of sleep.

A locally based study, led by cognitive neuroscientist Professor Michael Chee, found that people who lack sleep seem more likely to make risky choices that give higher returns.

His team picked gamblers as they make good 'lab rats'.

The study looked at 'quantitative decisions under conditions of measurable risk', Prof Chee explained.

The participants were given choices between high-risk betting with the opportunity of a large payout and low-risk option with modest gains.

A brain region called the nucleus accumbens, which is involved with reward, became more active when risky choices were made that promised a high pay-off.

Losses triggered a reduced response in the insula, another part of the brain that helps evaluate the emotional significance of events.

The scientists, using brain scanners, then studied the brain functions of these sleep-deprived gamblers and learnt why poor choices are often made when a person did not have enough rest.

Prof Chee said: 'People should not view sleep deprivation as a nuisance but something real. I think it's inappropriate to live in a manner that is out of touch with biology.'

Understanding why people make poorer choices when sleep-deprived is important, he felt.

'Not only because of the increasing numbers of persons affected, but also because there exist today unprecedented opportunities to incur damaging losses by such means as online gambling,' he said.

About 2.1 per cent of Singapore's population has been identified as having a gambling problem.

So, ahead of the integrated resorts opening here, the National Council on Problem Gambling wants to come up with a code of practice on responsible gambling that can be 'effectively administered and implemented'.

Mrs Mildred Tan, chairman of the council's public communications sub-committee, said such a code will put social safeguards in place to tackle and prevent problem gambling.

The draft code, which was adapted from the Responsible Gambling Code of Practice in Queensland, Australia, is now being refined.

The trend in developed countries suggests that increasingly, people are sleep-deprived.

Experts point to disasters such as air crashes as examples of what can happen when people lack sleep.

However, others say that humans are diurnal, and have learnt to adapt themselves to sleeping less and still operate at optimal levels.

Dr Heng Chin Tiong, a consultant with the surgery division at Tan Tock Seng Hospital, said a small number of people function perfectly well on only three to four hours of rest.

'Endurance can be built,' said Dr Heng, who recently performed a 15-hour surgery together with a colleague.

He added that restricting doctors to eight-hour shifts would mean they would not be able to last when required to perform long operations.

'Perhaps a study should be done on the errors incurred when doctors hand over to each other after their shifts and compare the percentage of errors committed during sleep deprivation. Things get lost in translation,' he summed up.