An accidental discovery about the effects of electrical stimulation on the brain suggests a potential treatment for people suffering from memory loss.

Scientists at Toronto Western Hospital said Wednesday their attempts to curb the appetite of a 50-year-old obese man using electrodes implanted in his brain triggered detailed decades-old memories.

Their discovery was published in Wednesday's issue of the Annals of Neurology, a peer-reviewed journal.

The man, who did not wish to be identified, has a lifelong history of obesity and has been unable to shed weight despite a variety of treatments.

Neurosurgeon Dr. Andres Lozano and his team were trying to suppress the man's appetite by stimulating parts of his hypothalamus when he suddenly experienced a feeling of déjà vu.

The man reported the perception of being in a park with friends 30 years ago, and as the intensity of the stimulation increased, the details became more vivid. "The scene was in colour. People were wearing identifiable clothes and were talking, but he could not decipher what they were saying," the researchers wrote.

The discovery was surprising because the hypothalamus is not usually associated with memory. But the parts of the hypothalamus that were stimulated are estimated to be close to the fornix, an arched bundle of fibers that carries signals within the limbic system, which is involved in memory and emotions.

"Well, it was a eureka moment, because we were looking for an effect on appetite," said Lozano.

"We knew it was very significant immediately. Because whenever you find something unexpected, you're not biased. And so it tells you that you're onto something that's probably quite real, and quite significant."

"I think that in scientific discoveries these are the best ones. The ones you're not expecting."

Deep brain stimulation has been used to treat Parkinson's disease and other movement disorders, and scientists are now studying it for its potential to treat conditions such as cluster headaches and aggressiveness.

The process involves boring holes through the skull to plant electrodes that touch particular parts of the brain and are connected to a pacemaker-like device that sends an electrical current into the brain.

While the treatment at Toronto Western Hospital did depress the man's appetite, he did not lose weight. Lozano said the man "overrode" or ignored the loss of hunger and continued to eat.

Dr. John Hart, a spokesperson for the American Academy of Neurology and medical scientific director of the Centre for Brain Health at the University of Texas at Dallas, called the work intriguing. But he said he'd want to see more evidence that stimulating this part of the brain is activating the pathways the researchers believe they are activating.

The researchers tested the man's ability to learn lists of paired objects after three weeks of continuously stimulating his hypothalamus. He scored higher on tests involving identifying pairs of words previously seen when the electrodes were turned on. But he was no better at other memory tasks.

"So it wasn't that he just became more attentive or aware or had better general processing. It really had to do with this very specific aspect of memory," McAndrews said.

Scientists are now applying the technique in the first trial of the treatment in three patients with Alzheimer's disease.

With files from the Canadian Press