Why Do We Forget Things? Flies May Have the Answer

In a series of animal experiments, researchers examined the interplay among memory, forgetting, sleep, and activity.

Fruit flies (Drosophila) were exposed to an odor that was associated with an electric shock. Learning to avoid the odor was linked to increased activity, driven by an intracellular calcium signal, of a specific group of dopaminergic neurons connecting to the fly's memory center. The same set of neurons appeared to drive neuronal plasticity that makes the nervous system more responsive to a variety of external stimuli. These neurons were turned on by locomotor activity and inhibited by sleep. Flies forgot the learned avoidance if they were active after learning, but they retained the memory hours later if sleep was induced by a…