Despite being separated by a 560-million-year evolutionary chasm, the basal ganglia of lampreys and mammals (including humans) are strikingly similar. They contain the same regions, organized and connected in the same way. Within these regions lie neurons with the same electrical properties, communicating with one another using the same chemical messengers. These findings led Grillner and Stephenson-Jones to the stunning conclusion that “practically all details of the basal ganglia circuitry had developed some 560 million years ago.”
