If you are always seeing the light at the end of the tunnel, be warned -- it could be an oncoming train.

So says a study published Sunday in the journal Nature Neuroscience, which concludes that our well-known penchant for donning rose-tinted glasses may be a failure to store risk awareness in a key part of the brain.

Tali Sharot, a professor at University College London, was intrigued as to why so many people, even when facing long odds or bleak prospects, remain stubbornly, even pathologically, optimistic.

To learn more, 19 volunteers were asked to take part in an experiment.

Sharot and colleagues monitored subjects in a functional magnetic resonance imaging (fMRI) scanner as they were confronted with life situations ranging from unpleasant to catastrophic.

Having their car stolen, getting fired from their job, developing Parkinson's disease or cancer were among 80 scenarios evoked.

After each hypothetical disaster, the volunteers were asked to estimate the odds of the misfortune happening to them. While still in the scanner, they were then informed of the true average probability of the risk.

Sometime later, the volunteers once again quantified the odds for personally experiencing each scenario.

The researchers found that the volunteers updated their initial estimates -- but only when the true figures were less gloomy.

If, for example, they had predicted a 40 percent chance of contracting cancer but the average likelihood turned out to be 30 percent, they were far more likely to adjust their estimate sharply downward.

But if the odds were worse than originally thought, the volunteers simply ignored the true statistics.

"Our study suggests that we pick and choose the information that we listen too," said Sharot. "The more optimistic we are, the less likely we are to be influenced by negative information about the future."

In the brain scans, all participants showed increased activity in their frontal lobes, which is strongly associated with emotional control, whenever the real numbers were better than expected.

The activity indicated that the new information was being processed and stored.

But when the news was more dire than the first guess, respondents who had rated highest for "optimism" in a personality test, taken beforehand, showed the least activity in their frontal lobe.

Sharot said the work showed that unbridled optimism had unperceived risks.

"Seeing the glass as half full rather than half empty can be a positive thing -- it can lower stress and anxiety, and be good for our health and wellbeing," she said.

"But it can also mean that we are less likely to take precautionary action, such as practicing safe sex or saving up for retirement."