Lashley failed to find the engram—his experimental animals were still able to find their way through the maze, no matter where he put lesions on their brains.
But, if manipulating engram cells can add, delete, and modify memories in predictable ways, that does mean engrams are a useful model for studying memory.
The researchers taught a mouse to associate a sound with a shock and then pumped the engram cells, where they knew that memory lived, full of this light-sensitive protein.