Earlier experimental studies by one of us (Kelso, 1981a, 1984) have shown that abrupt phase transitions occur in human hand movements under the influence of scalar changes in cycling frequency. Beyond a critical frequency the originally prepared out-of-phase, antisymmetric mode is replaced by a symmetrical, in-phase mode involving simultaneous activation of homologous muscle groups. Qualitatively, these phase transitions are analogous to gait shifts in animal locomotion as well as phenomena common to other physical and biological systems in which new "modes" or spatiotemporal patterns arise when the system is parametrically scaled beyond its equilibrium state (Haken, 1983). In this paper a theoretical model, using concepts central to the interdisciplinary field of synergetics and nonlinear oscillator theory, is developed, which reproduces (among other features) the dramatic change in coordinative pattern observed between the hands.

Conditions that give rise to phase shifts among the limbs when an animal changes gait are poorly understood. Often a "switch mechanism" is invoked that has a neural basis which remains speculative. Abrupt phase transitions also occur between the two hands in humans when movement-cycling frequency is continuously increased. The asymmetrical out-of-phase mode shifts suddenly to a symmetrical in-phase mode involving simultaneous activation of homologous muscle groups. The boundary between the two coordinative states is indexed by a dimensionless critical number, which remains constant regardless of whether the hands move freely or are subject to resistive loading. Coordinated shifts appear to arise because of continuous scaling influences that render the existing mode unstable. Then, at a critical point, bifurcation occurs and a new stable (and perhaps energetically more efficient) mode emerges.

Neural ensembles oscillate across a broad range of frequencies and are transiently coupled or “bound” together when people attend to a stimulus, perceive, think and act. This is a dynamic, self-assembling process, with parts of the brain engaging and disengaging in time. But how is it done? The theory of Coordination Dynamics proposes a mechanism called metastability, a subtle blend of integration and segregation. Tendencies for brain regions to express their individual autonomy and specialized functions (segregation, modularity) coexist with tendencies to couple and coordinate globally for multiple functions (integration). Although metastability has garnered increasing attention, it has yet to be demonstrated and treated within a fully spatiotemporal perspective. Here, we illustrate metastability in continuous neural and behavioral recordings, and we discuss theory and experiments at multiple scales suggesting that metastable dynamics underlie the real-time coordination necessary for the brain's dynamic cognitive, behavioral and social functions.