Dual representation of the hand in the cerebellum: activation with voluntary and passive finger movement.

Early electrophysiological studies during sensory stimulation in the anesthetized cat and more recent functional imaging studies during voluntary movement in humans have provided evidence for two separate representations of the body in the anterior and posterior lobes of the cerebellum; however, the functional role of these body maps in motor and sensory processing is not known. The aims of the present study were to determine whether this dual representation is also present during passive movement, and to compare the pattern of activation with that obtained during voluntary movement. Functional MRI measurements were undertaken in 14 subjects who performed right index finger flexion and extension movements at approximately 1 Hz, or had their finger moved passively at the same rate and through the same angle using a pneumatic device. During passive movement, dual activation was detected in the ipsilateral cerebellum, in the anterior lobe, and in the posterior lobe. A similar pattern of activation was observed during voluntary movement; however, the overall magnitude was about doubled. These data provide evidence for a dual ipsilateral representation of the hand in the rostral and caudal cerebellar cortex during passive as well as voluntary movements, with the rostral representation being the dominant one, and indicate that both of these areas are involved in kinesthetic sensory and motor processing.