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This chapter presents an overview of two major developments in the field of motor control: the referent configuration hypothesis (equilibrium-point hypothesis) and the theory of synergies (using the computational apparatus of the uncontrolled manifold hypothesis). It is suggested that a control hierarchy based on referent configurations at the whole-body, joint, and muscle levels may use synergic mechanisms to stabilize shifts of the task-related referent configuration expressed in salient for the motor task variables. On the other hand, control with referent configurations can itself lead to synergic relations within an ensemble of elemental performance variables that stabilize important performance variables produced by the ensemble as a whole. Relations between the notions of referent configuration and synergy and the control of vertical posture are discussed. Changes in synergy indices are described prior to a planned quick action or a reaction to a self-triggered perturbation. These phenomena, termed anticipatory synergy adjustments, share many common features with the well-known phenomena of anticipatory postural adjustments. A hypothesis is offered that anticipatory postural adjustments represent a superposition of two processes: anticipatory synergy adjustments with a minimal net mechanical effect and the generation of net forces and moments of force that are expected to counteract the anticipated perturbation.

The final part of the book addresses two issues: modeling of synergies and possible synergic organization of non-motor functions such as the language and the sensory function. Within the first issue, relations of synergies to the control theory is discussed with a brief overview of the central issues of the control theory such as open-loop and closed-loop control, and optimal control. Two models of synergies are described in more detail. One of them offers a neural network with back-coupling loops as the mechanism for multi-digit synergies. The other one suggests a scheme within which synergies emerge without any explicit feedback mechanisms. Further, the focus shifts to two aspects of synergies within the equilibrium-point hypothesis. One of them suggests that the principle of equilibrium-point control can by itself lead to synergies. The other deals with possible synergies in the hierarchy of control variables within the reference configuration hypothesis. The next two sections in this Part develop the notion of synergies for the sensory systems and for the production of human language. Multi-sensory interactions and synesthesia are described as possible reflections of sensory synergies. The book ends with an overview of its main points and a list of unsolved problems.

This chapter presents an autobiography of Emilio Bizzi. Bizzi's research formed the basis of a comprehensive theory—the equilibrium-point hypothesis—which accounts for how the central nervous system solves the complex computational problem of executing limb movements. Recently, his laboratory provided evidence that internal representations of limb dynamics are built by combining modular primitives found in the spinal cord as well as other building blocks in higher brain structures. His early years, career, and achievements are discussed.

The seventh part of this book deals with possible neurophysiological mechanisms involved in motor synergies. It starts with a discussion of the structure-function controversy in neurophysiology. Then, it presents reviews of the literature on the role in synergy formation of different structures within the central nervous system such as the spinal cord, the cerebellum, the basal ganglia, and the cortex of the large hemispheres. The review covers animal studies, studies of patients with different neurological disorders, and studies of healthy persons. Studies using transcranial magnetic stimulation are reviewed with respect to the equilibrium-point hypothesis of movement control. Relations between neuronal population vectors and performance variables are discussed. There is one more Digression in this part addressing the issue of localization of functions within brain structures.