New York, Jan 22 (IANS): A new study has found that our memories can not only travel back in time to retrieve events from the past but can also update past memories with important new information or details.

"Meaningful or emotional events can selectively preserve memory for previously encountered information that seemed insignificant at that time," said study lead author Joseph Dunsmoor, post-doctoral fellow at New York University.

In a series of experiments, the team examined the fate of seemingly inconsequential information that was, or was not, later made more meaningful - with the aim of understanding it and how past memories are updated with new emotional learning.

Participants were asked to identify a series of images of animals and tools .

However, upon being shown one category of images - either animals or tools - they received a mild shock to make one category of images emotionally meaningful.

Memory was then tested for all the images seen during the experiment.

Those who received the shock while viewing animal images were better able to recall those images than images of the tools which they saw without the shock.

The researchers also discovered that this emotional learning reached back in time to influence memory for the images seen before the learning procedure - when no shocks were possible.

In other words, subjects were able to recall an ordinary memory because it was later categorically linked ("animal" or "tool") to emotional learning.

"This enhanced memory for prior mundane events was only observed af ter a delay, suggesting that this retroactive memory enhancement occurs by facilitating long-term memory storage," Dunsmoor added.

In a nutshell, emotional learning can lead to the strengthening of older memories, concluded the study that appeared in the journal Nature.