Synergy control in subcortical circuitry: Insights from neurophysiology

Synergy control in the brain is likely to a large extent delegated to subcortical circuitry, with a focus on spinal circuitry and add-on capability provided by the spinocerebellar system for complex synergies. The advantage with this organization is that there is a tight connection, in the sense of shorter delays, between sensor feedback and the continuously updated motor command. By involving the sensory feedback in the motor command, the brain can make sure that the relevant biomechanical properties are properly compensated for. A consequence of this arrangement is that the neocortex, from which all voluntary motor commands originates, needs to learn the properties of the subcortical circuitry rather than the full details of the high-dimensional biomechanical plant. As the subcortical circuitry appears to have primarily linear properties, this arrangement makes it possible for the voluntary system to add synergy components linearly.