By the 1950s, two separate principles had grown out of Lashley's research: mass action and equipotentiality. "Mass action" refers to the idea that the rate, efficacy and accuracy of learning depend on the amount of cortex available. If cortical tissue is destroyed following the learning of a complex task, deterioration of performance on the task is determined more by the amount of tissue destroyed than by its location. "Equipotentiality" refers to the idea that one part of the cortex can take over the function of another part; within a functional area of the brain, any tissue within that area can perform its associated function. Therefore, to destroy a function, all the tissue within a functional area must be destroyed. If the area is not destroyed then the cortex can take over another part. These two principles grew out of Lashley's research on the cortical basis of learning and discrimination.