That first kiss

Have you ever wondered why you can't remember what you were doing five minutes ago, but clearly recall distant events such as your first kiss?

The answer, say scientists, is in the interaction between your amygdala and your hippocampus.

The amygdala is the part of the brain responsible for the emotions, while the hippocampus is concerned mainly with memory.

A dramatic event which exercises both of these sections of the brain at once is likely to remain locked in the memory for life.

The findings might account for the fact that, more than 40 years after his death, most people of the right age can still remember exactly what they were doing when they heard that John F. Kennedy had been assassinated.

Other examples that linger in the memory include England winning the World Cup in 1966, Prince Charles's marriage to Diana, the moment Neil Armstrong stepped on the moon in 1969 and the 9/11 terrorist attacks on America.

Lead researcher Florin Dolcos, of Duke University in North Carolina, said: 'We found evidence that the interaction between the emotional and memory regions occurred more systematically and consistently during the formation of emotional memories.'

In the study, volunteers looked at a series of pictures showing events which involved either positive or negative emotions or were judged to be 'neutral' and of no emotional impact.

Positive pictures included romantic scenes and sporting triumphs, negative images included aggressive acts and injury victims, and neutral pictures simply showed buildings or people shopping.

Meanwhile the volunteers ' brains were scanned using magnetic resonance imaging, which shows changing levels of blood flow to different areas of the brain.

Analysis of the results showed that emotionally charged pictures created increased levels of activity in the amygdala, as well as in the hippocampus. Neutral pictures had no effect on the emotion centre, as expected.

Moreover, the strength of activity in the amygdala and hippocampus was closely matched while viewing images intended to stimulate feelings, said the researchers.

They say this suggests that the two areas were interacting to help the brain successfully 'encode' the memory or store it away for future recall, says a report published today in the journal Neuron.

Neutral memories, on the other hand, engage only the hippocampus and are likely to be stored away only short-term and quickly diminished or replaced by memories of other unremarkable events.

Memory recall tests backed this up by showing that the volunteers were better able to recall the pictures with an emotional element.

Mr Dolcos, a postdoctoral research associate, said he hoped the findings could help aid understanding of conditions such as depression, which may involve obsessive reflection on negative memories, or aspects of posttraumatic stress disorder such as flashback memories.