In case you weren't aware, we are currently living in a world where we can activate brain cells in mice by turning on a light.
Recent studies using optogenetics have shed light (ha) on how memories are stored, accessed, and manipulated. An article from CNN last year explained how false memories can be implanted in mice, and another recent study reversed emotions associated with certain memories.
How does this work? From the CNN article:
Tonegawa's team started by identifying cells in the hippocampus, a seahorse-shaped brain structure that encodes a memory for a particular experience.
Then they "labeled" these information-rich cells, genetically altering them with a light-sensitive protein called channelrhodopsin. As a result, shining a blue light on these cells activated them.