How to Erase a Memory — And Restore It

One night, the ancient Chinese philosopher Zhuangzi, according to legend, fell into a deep sleep. That night, he dreamed famously that he was a butterfly, forgetting his identity as the widely respected and enlightened teacher Zhuangzi as he flew threw distant meadows, until he awoke — confused and contemplating whether he was now a butterfly, passively imagining his own existence as a man. There is now at least one type of creature who may share in Zhuangzi’s deep musings.

Scientists at the UC San Diego School of Medicine, in the first study of its kind, demonstrated the ability to repress and restore memories in rodents through manipulating their brain waves. It may be surprising to some that rodents are capable of retaining memories to begin with, much less wonder how one goes about erasing a memory.

The researchers focused on optic nerves that had been genetically modified in several lab rats, exposing them to light waves. While the rats focused on the bright lights, mild electrical shocks were delivered to their feet — not enough to harm them, but a strong enough warning that they soon showed fearful behaviors whenever the lights were turned on — making attempts to escape and avoid their handlers — a sure sign that they were conditioned to fearing the light waves.

A second, pulsing light targeted connections between nerves in the rodents’ brains at lower frequencies, and immediately afterward, the rats no longer showed signs of fear when exposed to the original bright lights as they had moments before — the association between the bright light and pain was quickly repressed.

So how were they reconditioned so easily? After using a higher frequency of light to target the same nerve connections, the rats became fearful once again when exposed to the original light source used at the beginning of the study. They had no need to be reconditioned — but merely recalled what they had learned already.

To some, this scenario may sound like something out of a dystopian science fiction novel, an assassin who relearns their ability to kill, but there’s a whole host of reasons to be optimistic about this new discovery. The study, published in Nature, has the potential to bring hope to many people suffering with Alzheimer’s, as scientists continue to study the relationship between wave frequencies and synapses in the brain, delaying the onset of dementia by keeping these nerves intact, while allowing patients to retain memories. It may even allow us to one day store memories at will, to freely turn back to and analyze at leisure.

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