Spinal circuits for motor learning

- Cerebellar-like modules for motor learning may be present in spinal circuits.
- Renshaw cells provide predictive input to motoneurons.
- Motoneurons function as comparators between predictive and instructive inputs.
- Homeostatic mechanisms govern biophysical properties of motoneurons.
- These principles point to mechanisms and circuits for spinal plasticity after injury.

Studies of motor learning have largely focussed on the cerebellum, and have provided key concepts about neural circuits required. However, other parts of the nervous system are involved in learning, as demonstrated by the capacity to 'train' spinal circuits to produce locomotion following spinal cord injury. While somatosensory feedback is necessary for spinal motor learning, feed forward circuits within the spinal cord must also contribute. In fact, motoneurons themselves could act as comparators that integrate feed forward and feedback inputs, and thus contribute to motor learning. Application of cerebellar-derived principles to spinal circuitry leads to testable predictions of spinal organization required for motor learning.