How to Insert a Memory Into the Brain of a Sleeping Mouse

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Photo: Oktay Ortakcioglu/Getty Images

The lab mice awoke with happy memories… that researchers had inserted into their brains while they slept. New research in Nature Neurscience is the latest proof that we may soon live in a Philip K. Dick short story, where synthetic memories can be created via neural stimulation. 

Hyperbole aside, here’s how they did it. The researchers set out to test the following hypothesis: Animals consolidate memories while sleeping by reactivating neurons associated with the remembered experience. In five mice, the researchers used a clearly defined spatial memory. Each mouse had electrodes implanted in its hippocampus, the structure associated with memory. The electrodes recorded neural activity while the mouse explored a new environment. By monitoring the recorded signals, the researchers could identify spikes of electrical activity in certain neurons that were associated with a certain place in the chamber.

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Then each mouse took a one-hour nap. During that snooze the researchers continued to watched the signals from the hippocampus. They waited for moments when those place-associated neurons lit up with activity, suggesting that the mouse was recalling its experience. (Interestingly, this didn’t occur often during the REM sleep in which we dream.) On that activity cue, the researchers used a second set of electrodes to stimulate the brain’s medial forebrain bundle, a structure associated with the sensation of pleasure. Essentially, the scientists were teaching the mouse to associate that certain location with a reward. 

When each mouse awoke, it was sent back into the chamber, while the researchers watched to see where it would hang out. These five mice did not wander at random, but instead showed a clear preference for the place now associated with good feelings. 

It’s a small study, but a fascinating contribution to the new field of memory hacking. Another recent experiment showed a way of turning bad memories into good ones in mice, and DARPA is funding research on memory prosthetics for humans. One day we may look back on these early experiments, and remember them fondly—thanks to the electrodes implanted in our brains. 

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