| Abstract | [Introduction]
Students of the neural basis of cognition might well take as their dictum the first phrase in the gospel according to St John: “In the beginning was word.” In this chapter, we beg to differ and side instead with Goethe’s Faust who, not satisfied with the accuracy of the biblical statement, proposed a rather different solution: “Im Anfang war die Tat”-”In the beginning was the act.” Certainly, if there is a lesson to be learned from the field of neuroembryology, it is that motility precedes reactivity; there is a chronological primacy of the motor over the sensory. Although one of our main premises is that any distinction between sensory and motor is an artificial one (cf. Kelso, 1979), this brief sojourn into developmental embryology affords what we take to be a main contrast between the topic of concern in this chapter-the control and coordination of movement-and the subject matter of the rest of this book.
Our goals in this chapter are twofold. First, we want to describe some of the main developments in the field of movement control (as we see them) that have occurred in the last six to seven years. The developments hinge around a central problem that has continued to plague the physiology and psychology of movement almost since its inception, that is, the identification of significant units of coordination and control. In the last Neuroscience’s Research Program Bulletin that dealt specifically with motor control, Szentagothai and Arbib (1974) suggested that :
While the term synergy has not been explicitly defined here, it is evident that the traditional Sherringtonian usage is too restrictive to capture the concepts... One now awaits a definition of synergies to revitalize motor systems research along the behavioral lines of investigation successfully used in the visual system. (p. 165)
Much earlier, of course, the Soviet school under Bernstein’s dominant influence (cf. Bernstein, 1967) has advocated the synergy as a significant unit, and the idea was taken up seriously in this country by Greene (1972), Boylls (1975), Fowler (1977), Turvey (1977), Kelso (1979), and Saltzman (1979a,b) among others. In fact, Boylls (1975) provided an elegant definition of synergy (or linkage, in his terms), which contrast sharply with the traditional Sherringtonian concept: A linkage is a group of muscles whose activities covary as a result of shared afferent and/or efferent signals, deployed as aunit in a motor task.
A number of laboratories, including our own, have been working out the details of functional synergies (or, synonymously, muscle linkages or coordinative structures). In the first part of this chapter, we explain briefly why the synergy concept is necessary, how synergies can be identified in many different activities, what their chief characteristics are, and how they are modulated by various sources of contextual information. All along, we try to show that there is a subtle and mutually dependent relationship between the small-scale, neural, informational aspects of the system and the large scale, power-producing machinery-the muscle dynamics. The first part of this chapter is largely review, with a few novel nuances, but some the organizational features that emerge are worthy of not in that they compare in an interesting way with recent theorizing about neuronal assemblies and brain functions (cf. Edelman & Mountcastle, 1978). At the end of the chapter, we make these comparisons explicit because they suggest a common ground for understanding the coherent behavior of muscle and neuronal ensembles.
Although we can supply a solid justification for the use of the synergy concept, and although we can provide hints-from the motor control literature-about how synergies can be regulated to accomplish particular acts, a principled basis is still required for understanding how the many free variables in the motor system can be harnessed in the first place. How do sable spatiotemporal organizations arise from a neuromuscular basis of many degrees of freedom? And what guarantees their persistence and stability? What principles underlie the cooperative behavior among muscles that is evident during coordinated activity?
In the second part of the chapter, we take up these and related questions seriously. In contrast to “machine theories,” which consider the many degrees of freedom to be regulated as a “curse” (cf. Bellman, 1961) and nonlinearities as a source of complication (cf. Stein, 1982), we advocate a set of “natural” principles gleaned from systems that require many degrees of freedom and in which nonlinearities are requisite conditions for the emergence of ordered phenomena (cf. Kelso, 1981; Kelso, Holt, Kugler, & Turvey, 1980; Kugler, Kelso, & Turvey, 1980, 1982; Turvey, 1980; see also Chapter 12, this volume). This “natural” perspective (Kugler, et al, 192) takes its impetus from (and is parasitic on) contemporary physics, and views the problem of coordination and control as continuous with, and a special case of, the more general problem of cooperative phenomena (cf. Haken, 1977). In this view, autonomy, self-organization, and evolution of function are stressed as system attributes. Our guess is that these attributes will prove difficult, in the long run, for the student of action to ignore, and, to the extent that they pertain to a theory of brain function, the cognitive neuroscientist as well. |
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