Researchers identify mechanism behind associative memory by exploring insect brains

The Memory of Smells
Scientists have long wondered how we manage to remember smells despite the fact that each olfactory neuron in the epithelium only survives for about 60 days, to be replaced by a new cell. In most of the body, neurons die without any successors. But as the olfactory neurons die, a layer of stem cells beneath them constantly generates new olfactory neurons to maintain a steady supply.

“The riddle was, how can we remember smells when these neurons are constantly turning over and the new crop has to form new synapses?” says Buck. “Now we know the answer: Memories survive because the axons of neurons that express the same receptor always go to the same place.”

And so some stages of olfaction are beginning to yield to researchers. But many mysteries remain. For example, what happens to information about smells after it has made its way from the olfactory bulb to the olfactory cortex? How is it processed there? How does it reach the higher brain centers, in which information about smells is linked to behavior?

Some researchers believe that such questions can best be answered by studying the salamander. This lizard-like creature’s nasal cavity is a flattened sac. “You can open it up more or less like a book” to examine how its olfactory neurons respond to odors, says John Kauer, a neuroscientist at Tufts Medical School and New England Medical Center in Boston, Massachusetts, who has been working on olfaction since the mid 1970s.

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- Maya Pines
Howard Hughes Medical Institute