Memories Can Be Injected and Survive Amputation and Metamorphosis

Memories Can Be Injected and Survive Amputation and Metamorphosis

Marco Altamirano

Glanzman now believes that synapses are necessary for the activation of a memory, but that the memory is encoded in the nucleus of the neuron through epigenetic changes. “It’s like a pianist without hands,” Glanzman says. “He may know how to play Chopin, but he’d need hands to exercise the memory.” 
The work of Douglas Blackiston, an Allen Discovery Center scientist at Tufts University, who has studied memory in insects, paints a similar picture. He wanted to know if a butterfly could remember something about its life as a caterpillar, so he exposed caterpillars to the scent of ethyl acetate followed by a mild electric shock. After acquiring an aversion to ethyl acetate, the caterpillars pupated and, after emerging as adult butterflies several weeks later, were tested for memory of their aversive training. Surprisingly, the adult butterflies remembered—but how? The entire caterpillar becomes a cytoplasmic soup before it metamorphosizes into a butterfly. “The remodeling is catastrophic,” Blackiston says. “After all, we’re moving from a crawling machine to a flying machine. Not only the body but the entire brain has to be rewired.”

It’s hard to study exactly what goes on during pupation in vivo, but there’s a subset of caterpillar neurons that may persist in what are called “mushroom bodies,” a pair of structures involved in olfaction that many insects have located near their antennae. In other words, some structure remains. “It’s not soup,” Blackiston says. “Well, maybe it’s soup, but it’s chunky.” There’s near complete pruning of neurons during pupation, and the few neurons that remain become disconnected from other neurons, dissolving the synaptic connections between them in the process, until they reconnect with other neurons during the remodeling into the butterfly brain. Like Glanzman, Blackiston employs a hand analogy: “It’s like a small group of neurons were holding hands, but then let go and moved around, finally reconnecting with different neurons in the new brain.” If the memory was stored anywhere, Blackiston suspects it was stored in the subset of neurons located in the mushroom bodies, the only known carryover material from the caterpillar to the butterfly.

In the end, despite its whimsical caricature of the science of memory, Eternal Sunshine may have stumbled on a correct premise. Not only do Glanzman and Blackiston believe their experiments harbor hopeful news for Alzheimer’s patients, it also might be possible to repair deteriorated neurons that could, at least theoretically, find their way back to lost memories, perhaps with the guidance of appropriate RNA.