The study of how people’s memories of traumatic events are affected by what they were doing at the time could help to prevent accident victims from having flashbacks.

It could also explain the effectiveness of worry beads in reducing tension and why the tricoteuses of the French Revolution, who knitted while watching people being guillotined and inspired Dickens’ character Madame Defarge in A Tale of Two Cities, never apparently experienced post-traumatic stress disorder.

The research was conducted by Emily Holmes, a psychologist at the Brain Sciences Unit in Cambridge.

She said: “How people form a memory of a traumatic event affects how volatile it will be and how likely it is that they will experience intrusive images, or flashbacks, of that trauma.”

Dr Holmes recruited a team of 51 volunteers to watch a video of real car crashes showing dead bodies and a lot of blood. A third were asked to tap out a complex five-key sequence on a keypad while they watched. In a second experiment involving 60 volunteers, a third of the group was asked to watch the same film while counting down in threes from 985. All the volunteers kept diaries for a week to record any intrusive memories of the film.

The results showed that those who carried out the tapping task experienced fewer flashbacks than those who had watched while doing no task. Those who counted backwards experienced more flashbacks of the film in the following week.

Dr Holmes concluded that tasks such as tapping disrupted the sensory parts of the brain used for laying down information and memory.

Tasks such as counting backwards disrupted the parts of the brain responsible for interpreting information — the verbal or conceptual parts of the brain — but did not interfere with laying down memories. Doing this kind of task therefore did not decrease the number of flashbacks participants experienced.

Dr Holmes said that while it would be impossible to get people to start tapping a keypad during an accident, it might help if they were given similar tasks in the immediate aftermath of a traumatic event when memories were still being laid down.

“This research is at an early stage, but it does suggest there may be a psychological way to help to reduce intrusive memories after a trauma.

“It would be interesting to examine the use of these tasks in settings such as accident and emergency departments.

“A psychological task could be within an individual’s control, non-invasive and costeffective,” she told the British Psychological Society’s annual conference in London.

Dr Holmes said that, in a domestic setting, performingtasks such as knitting, ironing, sorting socks or doodling could have similar effects to tapping a pattern on a keyboard while doing more enjoyable things such as watching a ahorror film. Using worry beads might also have the same effect.

She also said that her research backed up the idea that the actions of the tricoteuses were therapeutic. “It could be that knitting could have protected them from having flashbacks.”

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