"The apparent capacity of any intact part of a functional brain to carry out… the functions which are lost by the destruction of [other parts". Another way of putting this is, the brain has the ability to use any functioning part of the brain to do what a damaged part of the brain no longer can do. Equipotentiality is subject to the other term Lashley coined the mass action principle. This principle postulates that the efficiency of any complex function of the brain is reduced proportionately to how much damage the brain as a whole has sustained, but not to the damage of any particular area of the brain. In this context when we use brain we are referring to the cortex.