Lashley's most influential research centered around the cortical basis of learning and discrimination. He researched this by looking at the measurement of behavior before and after specific, carefully quantified, induced brain damage in rats. Lashley trained rats to perform specific tasks (seeking a food reward), then lesioned specific areas of the rats' cortex, either before or after the animals received the training. The cortical lesions had specific effects on acquisition and retention of knowledge, but the location of the removed cortex had no effect on the rats' performance in the maze. This led Lashley to conclude that memories are not localized, but that they are widely distributed across the cortex. Today we know that distribution of engrams does in fact exist, but that the distribution is not equal across all cortical areas, as Lashley assumed. His study of V1 (primary visual cortex) led him to believe that it was a site of learning and memory storage (i.e. an engram) in the brain. He reached this erroneous conclusion due to imperfect lesioning methods.