Conserved temporal dynamics and vector superposition of primitives in frog wiping reflexes during spontaneous extensor deletions

We use spontaneous motor pattern deletions in spinal frogs to test a computational theory of movement construction. We hypothesize that at the spinal level, operating in isolation from the brain, the forces driving movements are constructed from summation of force-field primitives of fixed temporal dynamics, which can be expressed in the form F(r, (r)overdot, t) = Sigma(i)A(i)a(t + tau(i))phi(i)(r, (r)overdot) where A(i) is a scaling parameter, a(t) is a common timing dynamics for each primitive, time shifted for each by t(i) and phi(r, (r)overdot) are functions of limb state. In deletions, the force amplitudes, force directions and patterns behave as predicted by this model of movement construction based on summation of force-field primitives. (C) 2000 Elsevier Science B.V. All rights reserved.