Scientists performing experimental brain surgery on a man aged 50 have stumbled across a mechanism that could unlock how memory works. The accidental breakthrough came during an experiment originally intended to suppress the obese man's appetite, using the increasingly successful technique of deep-brain stimulation. Electrodes were pushed into the man's brain and stimulated with an electric current. Instead of losing appetite, the patient instead had an intense experience of déjà vu. He recalled, in intricate detail, a scene from 30 years earlier. More tests showed his ability to learn was dramatically improved when the current was switched on and his brain stimulated. Scientists are now applying the technique in the first trial of the treatment in patients with Alzheimer's disease. If successful, it could offer hope to sufferers from the degenerative condition, which affects 450,000 people in Britain alone, by providing a "pacemaker" for the brain.

A 50 year old man, dangerously obese, goes to the hospital for experimental brain surgery to suppress his appetite. A small piece of his skull is removed, and an electrical probe inserted deep into his brain tissue. It reaches his hypothalamus and current is switched on. Suddenly the patient -- awake through the procedure -- begins to speak uncontrollably about events in his past, events he had long forgotten. He remembers a day's walk in the park 30 years ago, complete with what people were wearing, all in vivid color. He sees them speaking to him, every motion they made. The intensity and level of detail of the memories is frightening.

The scene may read like the script of a bad science fiction flick but it comes from an unidentified patient at Ontario's Toronto Western Hospital. No one was more astonished than the man's doctors, who began to experiment further on him. Over the next few weeks, they continued testing. His ability to both learn and remember was substantially increased when the electrodes were turned on. Continuous stimulation also had a residual effect -- after the electrodes were off, there was still a slight benefit.