1. Karl S. Lashley’s hypothesis that large areas of cerebral cortex have similar potential to perform particular functions, including learning and other complex processes (e.g., maze navigation), so that intact cortical areas may take over functions of damaged or destroyed areas. Proposed in 1929 following experimental observations of the effects of different brain lesions on rats’ ability to learn a complex maze, the concept has been challenged by subsequent research showing that areas of cortex have relatively specific functions. Brain plasticity (adaptive shifting of function) is commonly observed after local cortical damage, however. See also mass action. 2. in learning theory, the principle that any pair of stimuli can be associated with equal ease, regardless of their nature or origin. Also called law of equipotentiality; principle of equipotentiality.