The research plan outlined in this proposal is part of a long-range study to understand the role of the cerebellum in the control and regulation of posture and movement. The specific aims of this proposal focus on the organization and representation of sensory information in spinal projection pathways and in the cerebellum. The dorsal spinocerebellar tract (DSCT) transmits to the cerebellum information derived from sensory receptors in muscle, joints and skin of the hind limbs. The content of the signals transmitted and their utilization by the cerebellum are not known, yet these are central to an understanding of cerebellar function as it relates to spinal motor functions. The proposed research will investigate neuronal population behavior in the DSCT and cerebellum by recording from large numbers of randomly sampled neurons, and by using statistical methods based on principal component analysis and correlation analysis. The main issues to be addressed are the nature of the information encoded and the way in which it is encoded. These issues will be examined in the context of a new working hypothesis about the functional role of the spinocerebellar system: It is proposed that the information transmitted by spinocerebellar pathways provides a sensory representation of limb stiffness which may be used to regulate stiffness as a background for posture and movement. Experiments will test specific issues related to this hypothesis. The research is expected to provide new evidence about the role of the nervous system in motor control. Motor control disorders constitute a major health problem with considerable economic consequences. Basic research, such as that proposed here, is needed to understand better the role played by neuronal structures like the spinal cord and the cerebellum in the normal control of posture and movement.