A memory trace, also know as an engram, is a theoretical means by which memories are physically stored in the brain. The actual method of storage of memory, whether by biophysical or biochemical means, is still being debated. However, the point of agreement is that memory appears to be spread over several areas of the brain rather than being sequestered in one area.
Researcher Karl S. Lashley, in his work between 1929 and 1950, attempted to locate the physical area where memory traces were stored. He trained rats to run mazes and once thoroughly trained, he performed surgery on the cortices of the rats' brains. He learned that although this surgery caused their performance to diminish somewhat, they did not forget how to run the mazes. Surprisingly, it was discovered that it didn't really matter what part of the brain was removed because these memories are apparently generalized throughout the brain structure. Although engrams are believed to exist the actual methods and locations of the process are still being researched and debated to this day.