What Sherrington missed: the ubiquity of the neural integrator

Despite its numerous illustrations unequivocally demonstrating the phenomenon, in Sherrington's Integrative Action of the Nervous System, he considered "integration" only in its spatial and coordinative aspects, and failed to notice time integration as an equally pervasive feature of all motor systems. First demonstrated in the oculomotor system by Robinson and others, in the vestibulo-ocular reflex, and then as a necessary component of the oculomotor "final common path" (another Sherringtonian concept), integration is manifested at two further levels: in generating optokinetic responses and in the mechanism of saccadic decision. But integration is not a purely oculomotor phenomenon: behind it lie two fundamental motor principles. First, that the brain operates in terms of change, implying differentiation in sensory systems and integration in motor ones. Second, that the molecular physiology of muscle contraction means that remaining still requires not only continual expenditure of energy but also continual computational effort--a firm and precise integrator.