Unpleasant memories can be wiped out by electric shock therapy used to treat psychiatric patients, a study has shown.
The discovery raises the possibility of helping victims of post-traumatic stress disorder by freeing them of their demons.
However, in Britain electroconvulsive therapy (ECT) is reserved only for certain forms of mental illness, including severe depression and mania.
ECT triggers a brief epileptic fit by delivering a jolt of electricity to the brain via electrodes placed on the head.
In the new study, researchers tested its effect on memory on 39 patients already receiving ECT for depression.
Participants were told two emotionally unpleasant stories presented in the form of a slideshow accompanied by a voice over. A week later story memories were "cued" by showing the first slide partially covered.
Immediately afterwards, one group of patients were given ECT.
A day later, patients were tested on what they could recall about events relating to the first slide. Those who had undergone ECT struggled, while the memories of patients who had not received the therapy were unaltered.
Only those memories that were reactivated by the cue were disrupted by ECT, according to the findings reported in the journal Nature Neuroscience.
The scientists, led by Dr Marijin Kroes, from the Donders Institute for Brain, Cognition and Behaviour at Radboud University in the Netherlands, wrote: "We found that a single ECT application in unipolar-depressed patients following memory reactivation disrupted reactivated, but not non-reactivated, memory for an emotional episode...
"Our data provide evidence for disruption of reactivated emotional episodic memories by invasive interference with normal neural activity."
Commenting on the results, Dr Aidan Horner, from the University College London Institute of Cognitive Neuroscience, said: "The ability to disrupt or even abolish specific memories, whilst leaving others intact, could have important therapeutic applications. For example, selectively disrupting memories in patients with psychological conditions, such as post-traumatic stress disorder.
"However, treatment using ECT is currently restricted to specific conditions (depressive illness, schizophrenia, and catatonia and mania). As such, any possible applications are at present limited to specific patient groups."
Developed in the 1930s, ECT was once widely used to treat a variety of psychiatric conditions but is now regarded as a drastic remedy for certain more serious conditions.