Cortical and segmental control during voluntary and postural activities in the human and the cat

The authors present several examples taken from their own work of changes in the input-output properties of neural circuits of the spinal cord and of the corticospinal pathway during a variety of natural motor tasks. The point is made that modulations of the effectiveness, or intensity of action, of these pathways depend on the motor task being executed, occur automatically, and serve to adapt the motor system to the biomechanical exigencies of the task. The authors also suggest that the control signals involved in reflex modulation are an intrinsic feature of the motor commands.