We tend to think of memory as an amorphous, almost undefinable thing floating around inside our brains, sparked or muted through chaotic electrical charges firing between neurons. Brain researchers have theorised about human memory storage devices called engrams, but the idea has always been conceptual.
Now, researchers at MIT have discovered they’re real. In mice, they pinpointed individual cells where memories of specific events were stored, and recalled those memories by shining light on those cells. “Our results show that memories really do reside in very specific brain cells, and simply by reactivating these cells by physical means, such as light, an entire memory can be recalled,” says Xu Liu, a co-author of the study, which was published in Nature.
Reading Memories With Light
Optogenics is a young field of study that allows scientists to activate specific genes by shining light on cells. For this study, the researchers identified a set of mouse brain cells that became active when the researchers gave the animal a little shock to the foot while it was exploring new surroundings. The researchers then genetically modified those cells to carry the gene for channelrhodopsin-2, a protein activated by light.
Later they released the mice into a different environment, and exposed those same cells to pulses of light. The mice crouched in fear in a defensive stance though there was no indication they’d be shocked again. The light alone seemed to be triggering the memory, which means it was stored in the cell activated by the light.
Modern Day Penfield Experiment
In the early 1900s, Wilder Penfield was trying to treat epilepsy patients while jolting neurons in the hippocampi. He found that for some, the neuron stimulation triggered detailed memories. That experiment engendered the theory that stimulating nurons directly could induce memory recall, but it hadn’t been proven until now.
Next up: memory lasers! Which would come in handy for handlers of politicians trying to recall the name of the government agencies they’d like to eliminate. No more “Oops” moments. [Geekosystem and MIT News]
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