The means by which traces of memory are stored, engrams, have only been hypothetical, which means we did not have an idea of the actual, concrete means by which memories are stored in the brain. However, in a new study, MIT researchers used optogenics — a combination of optical and genetic methods to control events in cells of living tissue, essentially the manipulation of cells so they’re sensitive and responsive to light — to show that memories are actually kept inside brain cells.
Susumu Tonegawa, Picower Professor of Biology and Neuroscience at MIT, explains that a memory can be triggered by physical stimulation, and in turn activation, of a specific subpopulation of brain cells. To do this, researchers identified a specific set of brain cells in a mouse that were active when said mouse was learning about new surroundings. Once those cells were identified, the researchers joined them up with the gene for channelrhodopsin-2, which is a protein activated by light used in optogenics.
The mice with the teamed up gene were then released into a controlled environment wherein they were delivered a mild shock to the foot after a few minutes, learning to be afraid of the environment. When the mice became afraid, the brain cells activated by that fear were tagged with channelrhodopsin-2. Then, when the mice were released into a different environment, they were exposed to pulses of light, which happened to trigger the fear from the first environment where they got shocked — signaled by the mice crouching over in a defensive stance — even though there was no indication of an incoming shock in the new environment. The defensive crouching suggests that the mice were recalling the initial memory of being shocked.
Co-author of the study, Xu Liu, says the results show that memories really do reside in specific brain 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.”
The results of this study probably won’t lead to something like memory guns, where we can shoot ourselves into remembering things, but realizing that engrams are physical instead of conceptual gives us insight into psychiatric disorders and certain degenerative diseases. As co-author of the study and graduate student Steve Ramirez puts it, “The more we know about the moving pieces that make up our brains, the better equipped we are to figure out what happens when brain pieces break down.”
(MIT News via ExtremeTech)
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