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Neuroscientists — scientists who study the brain — have long attempted to understand the nature of memory. Engrams, or complete memories that are encoded in the brain, now appear to be stored physically as opposed to conceptually, according to research published in the journal Nature .
Explains lead researcher Susumu Tonegawa of MIT:
We demonstrate that behavior based on high-level cognition, such as the expression of a specific memory, can be generated in a mammal by highly specific physical activation of a specific small subpopulation of brain cells, in this case by light.
The researchers altered a small portion of the brains of some mice, causing the cells to produce light-sensitive proteins. They then put the mice in a specific environment and delivered a mild shock, causing the mice to fear the environment. Later, they stimulated the brain cells with light. This caused the mice to experience fear, even though they were no longer in the environment in which they’d been shocked. The light-sensitive cells were the ones that had encoded the fear memory.
The researchers hope that this work will help to elucidate the nature of how the brain encodes memories, which could be relevant to work with patients who have lost memories due to disease, aging or injury.
Liu et al. Optogenetic stimulation of a hippocampal engram activates fear memory recall. Nature. 2012 Mar 22. doi: 10.1038/nature11028. [Epub ahead of print].