Eat to remember.

Eat to remember

Even an old dog can learn new tricksif enticed with enough food. Now, researchers at the Veterans Administration Medical Center in Sepulveda, Calif., have discovered how the reward of food may facilitate such learning in animals.

James F. Flood, Gary E. Smith andJohn E. Morley suggest in the May 15 SCIENCE that a gastrointestinal hormone released in mice during feeding can enhance memory by activating fibers in the peripheral nervous system. While in past work the hormone, cholecystokinin (CCK), has been associated with enhanced memory, says Morley, this is the first proposed mechanism for that link.

In their studies, the researchers firstshowed that hungry mice, fed immediately after learning a task, later remembered how to complete that task much better than did other mice, some of which were hungry and fed three hours after learning, others of which were well fed prior to the experiment.

Flood's group also showed that CCKinjected in the mice's abdomens mimicked the memory effects of feeding. The question then, says Morley, was how CCK, which is too large to cross the blood-brain barrier, is able to influence the brain. The researchers discovered that CCK enhanced memory only when a mouse's vagus nerve was intact. This nerve is part of the peripheral nervous system and is anatomically connected to a memory region of the brain. The researchers believe that CCK affects memory by activating vagus fibers leading from the gut toward the brain.

They suspect that the link betweengastrointestinal hormones and memory has given animals an evolutionary edge by helping them remember how they successfully found food in the past. As for humans, Morley says the lesson is that to be most memorable, the after-dinner speech should be given before dinner.