A team of doctors in Canada stumbled upon the finding while attempting to treat a morbidly obese man through deep brain stimulation (DBS).
The electrical stimulation caused the patient to experience vivid memories.
The findings, reported in the Annals of Neurology, potentially pave the way for electrical stimulation to treat disorders such as Alzheimer's disease.
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| The brain's limbic system was stimulated |
Lead researcher Professor Andres Lozano, of the Toronto Western Hospital, said: "This is a single case that was totally unexpected.
"We knew immediately this was important. We are sufficiently intrigued to see if this could help people with memory disorders."
The team had been trying to help a 50-year-old obese man with type 2 diabetes and sleeping disorders who had failed to respond to diet, medications and psychological help.
He had refused gastric surgery, and doctors decided deep brain stimulation, although experimental, was his best option.
It has been found to have an impact on appetite in animal tests, but has not been widely tested as a treatment for obesity in humans.
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| Electrodes are implanted in the brain under local anaesthesia, with the patient awake so their responses can be monitored.
The electrodes are stimulated by a "pacemaker" stitched into the chest. It has been used for more than a decade to treat tremor, and more recently to treat Parkinson's disease, chronic pain and depression. Side effects can include apathy, hallucinations, depression, and even compulsive gambling - but often they are temporary. |
However, it has been used to treat Parkinson's disease, chronic pain, severe cluster headaches and even depression with some success.
The technique involves implanting electrodes into the brain: in this case into an area in the limbic system called the hypothalamus, which is thought to control the appetite.
When the electrodes were stimulated by electrical impulses the patient began to experience feelings of deja vu.
He then had a sudden perception of being in a park with friends.
He felt younger, thought he was around 20-years-old, and his girlfriend of the time was there. He was an observer, and saw the scene in colour.
As the intensity of the stimulation increased, details in the scene became more vivid.
Memory tests
Following surgery, the patient recovered for two months. But later when the electrodes were stimulated for a second time, he experienced a similar effect.
After three weeks of constant electrical stimulation the patient performed better in memory tests than he had previously done.
A year later he again performed well in memory tests when the electrodes were stimulated, but less well when they were switched off.
The results suggest it might be possible to use deep brain stimulation directly to boost memory.
"We hopefully have found a circuit in the brain which can be modulated by stimulation, and which might provide benefit to patients with memory disorders," said Professor Lozano.
Professor Lozano is now leading a pilot study into whether deep brain stimulation can help people with early Alzheimer's disease. They are initially testing six patients.
Susanne Sorensen, of the Alzheimer's Society, said: "As it is difficult to experiment on the living human brain, big leaps in understanding have occasionally been made from unexpected results when treating something unrelated or observations from rare genetic diseases and unusual lesions.
"The observations of memories recovery made during this attempt to treat extreme obesity, could be just such a 'stroke of luck'."
Rebecca Wood, Chief Executive of the Alzheimer's Research Trust, welcomed the move but said further work was clearly needed.
She said: "It will be interesting to see whether this method offers any benefit to people with Alzheimer's.
"With the number of people with Alzheimer's forecast to double within a generation, we urgently need to find ways to tackle this awful disease, but research is hugely under-funded."
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