Sensorimotor interactions during locomotion: Principles derived from biological systems

Rhythmic movements in biological systems are produced in part by central ci rcuits called central pattern generators (CPGs). For example, locomotion in vertebrates derives from the spinal CPG with activity initiated by the bra in and controlled by sensory feedback. Sensory feedback is traditionally vi ewed as controlling CPGs cycle by cycle, with the brain commanding movement s on a top down basis. We present an alternative view which in sensory feed back alters the properties of the CPG on a fast as well as a slow time scal e. The CPG, in turn, provides feedforward filtering of the sensory feedback . This bidirectional interaction is widespread across animals, suggesting i t is a common feature of motor systems, and, therefore, might offer a new w ay to view sensorimotor interactions in all systems including robotic syste ms. Bidirectional interactions are also apparent between the cerebral corte x and the CPG. The motor cortex doesn't simply command muscle contractions, but rather operates with the CPG to produce adaptively structured movement s. To facilitate these adaptive interactions, the motor cortex receives fee dback from the CPG that creates a temporal activity pattern mirroring the s pinal motor output during locomotion. Thus, the activity of the motor corti cal cells is shaped by the spinal pattern generator as they drive motor com mands. These common features of CPG structure and function are suggested as offering a new perspective for building robotic systems. CPGs offer a pote ntial for adaptive control, especially when combined with the principles of sensorimotor integration described here.