Washington, Aug 12 - A study led by an Indian-American has untangled how long-lasting memories form in the brain, potentially opening the way to prevent and treat post-traumatic stress disorder.

'Although many things are known about memories that form from repeat experiences, not much is known with regard to how some memories form with just one exposure,' said Ashok Hegde, neurobiologist and anatomist at the Wake Forest University School of Medicine (WFUSM).

Scientists do know that people tend to remember extremely happy or sad occasions vividly because of the emotional connection, said Hegde, the lead study investigator.

Extreme emotions trigger the release of a chemical in the brain called norepinephrine, which is related to adrenaline. That norepinephrine somehow helps memories last a long time -- some even a lifetime.

For example, he said, when a person asks 'Where were you when the 9/11 attacks happened?' most people can recall immediately where they were and what they were doing when they heard the news.