Origin and advances of the equilibrium-point hypothesis.

This section is a collection of papers devoted to the equilibrium-point (EP) hypothesis. The first chapter (by Feldman and Levin) is a brief account of the past and present status of the hypothesis with suggestions for further development. The EP hypothesis emerged in the unique scientific atmosphere created by a group of researchers that is now known in the West as the Russian School of Physiology. The group was founded in approximately 1959 by the famous mathematician, Israel Gelfand, with the purpose of attracting specialists in mathematics, physics, engineering, chemistry and biology to join in what is now known as a multidisciplinary approach to biology in general and to the neural control of movement in particular. Two particularly talented scientists, Michael Tsetlin, a physicist, engineer and mathematician, and Victor Gurfinkel, a physician by training and former student ofNikolai Bernstein, were co-organizers of the group. The group also included, among many others, several physiologists (Gregori Orlovsky, Yakov Kots, Mark Shik, Inessa Keder-Stepanova, Levon Chailakhian, Yurii Arshavsky, Sergei Kovalev, Ivan Radionof, Michael Mirsky, Sasha Elner, EfimLieberman) and two physicists (Michael Berkinblit andVladimir Smolyaninof). Nikolai Bernstein gave a cycle of lectures on motor control for this group and his ideas werewell appreciated. At the time of the elaboration of the EP hypothesis, I was a PhD student at the Moscow Institute of Physics and Techniques under the co-directorship of Michael Tsetlin and Victor Gurfinkel. Several scientists were instrumental in bringing the ideas of the EP hypothesis into the West, starting from Michael Turvey, Emilio Bizzi, Neville Hogan, Tamar Flash, Francis Lestienne, Scott Kelso, James Houk, David Ostry, Yves Lamarre, Richard Nichols, and Mark Latash. The EP hypothesis resulted from the experimental analysis of the relationship between involuntarymovements elicited by unloading of the arm and intentional, self-initiated armmovements (Asatryan and Feldman 1965). The hypothesis was