"The research, described in the journal Nature, involved two groups of mice. One was a normal control and the other was genetically engineered to have Alzheimer's-like symptoms. Both groups were given a mild electric shock to their feet. The first group appeared to remember the trauma of the incident by showing fear when placed back in the box where they had been given the shock. The Alzheimer's mice, on the other hand, seemed to quickly forget what happened and did not have an upset reaction to the box.
"Their reaction changed dramatically when the scientists stimulated tagged cells in their brains in the hippocampus — the part of the brain that encodes short-term memories — with a special blue light. When they were put back in the box following the procedure, their memories of the shock appeared to have returned, and they displayed the same fear as their healthy counterparts."