The DBS surgery, attempted in the treatment of Parkinson's Disease, can also improve one's memory, Canadian researchers say.
Deep brain stimulation (DBS) involves implanting of electrodes in the brain.
The new finding means DBS can also be useful in treating Alzheimer's.
A team of doctors in Canada stumbled upon a new dimension to DBS while attempting to treat a morbidly obese man. The electrical stimulation caused the patient to experience vivid memories, it is reported in the Annals of Neurology.
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, BBC says.
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.
It has been used to treat Parkinson's disease, chronic pain, severe cluster headaches and even depression with some success.
In this case into an area in the limbic system of the brain 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.
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.
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."