As part of the study, to find out whether common variations in a gene called ADRA2B, which codes for the noradrenaline receptor, could be responsible for the variation in recall of emotional events from person to person, researchers showed photos of strongly positive, neutral and strongly negative emotional incidences to two large groups of people and asked the group members to recall them and illustrate them in writing.
One group had healthy Swiss citizens and the other included traumatised victims of the Rwandan genocide who were living in a refugee camp in Uganda.
The positive images included a grandfather with his grandchildren and a wedding scene. Negative ones included an accident victim with a head injury and images of devastating pollution spills.
Neutral images showed people walking in the street or talking on the phone.
The study found that in both groups, people with the ADRA2B gene variant were 'substantially more likely' to keep in mind both positive and negative pictures than people with other forms of the gene.
There was no variation in remembering the neutral images in either group.
However, Rwandans with the variant could recall negative emotional events toa much higher degree than the Europeans who carried it.
"The genetic variant is related to enhanced emotional memory. But it also appears to predispose people to stronger traumatic memories when something terrible happens," New Scientist magazine quoted de Quervain, as telling Nature Neuroscience.