also distinguished between his area 4 (coextensive with the primary motor cortex) and his area 6 (coextensive with the premotor cortex). Vogt and Vogt in 1919 also suggested that motor cortex was divided into a primary motor cortex (area 4) and a higher-order motor cortex (area 6) adjacent to it. Furthermore, in their account, area 6 could be divided into 6a (the dorsal part) and 6b (the ventral part). The dorsal part could be further divided into 6a-alpha (a posterior part adjacent to the primary motor cortex) and 6a-beta (an anterior part adjacent to the prefrontal cortex). These cortical fields formed a hierarchy in which 6a-beta controlled movement at the most complex level, 6a-alpha had intermediate properties, and the primary motor cortex controlled movement at the simplest level. Vogt and Vogt are therefore the original source of the idea of a caudal (6a-alpha) and a rostral (6a-beta) premotor cortex. Fulton in 1935 helped to solidify the distinction between a primary motor map of the body in area 4 and a higher-order premotor cortex in area 6. His main evidence came from lesion studies in monkeys. It is not clear where the term "premotor" came from or who used it first, but Fulton popularized the term. A caveat about the premotor cortex, noted early in its study, is that the hierarchy between the premotor cortex and the primary motor cortex is not absolute. Instead both the premotor cortex and primary motor cortex project directly to the spinal cord, and each has some capability to control movement even in the absence of the other. Therefore, the two cortical fields operate at least partly in parallel rather than in a strict hierarchy. This parallel relationship was noted as early as 1919 by Vogt and Vogt and also emphasized by Fulton. Penfield in 1937 notably disagreed with the idea of a premotor cortex. He suggested that there was no functional distinction between a primary motor and a premotor area. In his view both were part of the same map. The most posterior part of the map, in area 4, emphasized the hand and fingers and the most anterior part, in area 6, emphasized the muscles of the back and neck. Woolsey who studied the motor map in monkeys in 1956 also believed there was no distinction between primary motor and premotor cortex. He used the term M1 for the proposed single map that encompassed