A mathematical model for storage and recovery of motor actions in the spinal cord

Motor outputs are generated by the spinal cord in response to de-scending inputs from the brain. While particular descending commands generate specific outputs, how descending inputs interact with spinal cord circuitry to generate these outputs remains unclear. Here, we suggest that during development particular motor programmes are stored in premotor spinal circuitry, and that these can subsequently be retrieved when the associated descending input is received. We propose that different motor patterns are not stored in the spinal cord as a library of separate programmes, but that the spinal cord orthogonalises and normalises the various inputs, identifies the similarities and differences between them, and stores only the differences: similarities between patterns are recognised and used as a common basis that subsequent input patterns are built upon. By removing redundancy this can greatly increase the storage capacity of a system composed of a finite number of processing units, thus overcoming the problems associated with the storage limits of conventional artificial networks (e.g. catastrophic interference). Where possible we relate the various stages of the processing to the known circuitry and synaptic properties of spinal cord locomotor networks, and suggest experimental approaches that could test unknown aspects.