Reply to Strata et al.: Motor areas of the cerebral cortex project to the posterior vermis

The electrophysiological studies of Strata and colleagues in the cat were performed on the anterior vermis of the cerebellum (lobules I–V), rostral to the primary fissure (1). They found that the anterior vermis receives somatotopically organized input from the periphery and from the arm and leg representations of the cat sensorimotor cortex. These findings were consistent with classic and current body maps in the cat and monkey cerebellum (2) (Fig. 1). Similar maps have recently emerged from imaging studies of human subjects (e.g., ref. 3; for references and discussion about body maps in the cerebellum see ref. 4). In general, maps of cerebellar cortex show that the representation of the face is located caudal to the primary fissure in the posterior vermis (Fig. 1). The remainder of the posterior vermis from lobules VII to X was thought to lack a body representation and to be free of input from the cerebral cortex. This viewpoint is illustrated in every major textbook.

Fig. 1.

Classic map of body representation in the cerebellar cortex of the monkey (adapted with permission from ref. 2). Roman numerals designate some of the cerebellar lobules. The thick curved line between lobules V and VI indicates the primary fissure, which lies between the anterior and posterior lobes of the cerebellum. The cerebellar vermis lies along the midline. The dashed line indicates the border between the vermis and cerebellar cortex in the hemisphere. The posterior vermis consists of lobules VI through X.

Our findings challenge the classic perspective concerning the posterior vermis. We show that a portion of the posterior vermis (lobules VII–VIIIB, as well as lobule VIB) receives substantial disynaptic input from the cerebral cortex (figures 2 and 3 in ref. 5). This input originates not only from the primary motor cortex but also from multiple premotor areas in the frontal lobe. Indeed, approximately half of the input originates from premotor areas located on the medial wall of the hemisphere.

We did not emphasize sufficiently the distinction between the anterior vermis and the posterior vermis in our report. Thus, we are grateful for the letter from Prof. Strata and his colleagues (6) because it allows us to correct this oversight and at the same time clarify our observations about the posterior vermis of the cerebellum.