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In 1963, an article on “Tonus” (tone), written by Nikolai A. Bernstein and Yakov M. Kots. appeared in the second edition of the Bols'aja Medicinskaja Enciclopedija [Grand Medical Encyclopedia]. The paper is now published for the first time in the English language, with Mark L. Latash as translator. In accordance with then contemporary neurophysiology and neuropsychology, the paper presented “tone” as a graded phenomenon (as opposed to all-or-none), serving to prepare the segmental level for phasic contractions. Influenced by Granit and Matthews, the authors proposed that the suprasegmental level controls the threshold and the slope of the stretch reflex. In their introduction to the present edition, the editors understand this proposal in the context of low-dimensional control, that is. control in terms of one or a few variables (as opposed to central commands specifying all the details). Selected episodes from the history of low dimensional control and its logical counterpart, spinal intelligence, are used to illustrate how difficult these ideas were to accept. As so often in new scientific developments, confusion was the rule, and in this respect the paper on “Tonus” is no exception. In the epilogue, Kots gives his personal memories of the context in which the paper was written. At the time, he was working on “equitonometry” (equitonometric), measuring tonic balance with gravity eliminated. Results of equitonometric research quite naturally led to the idea that suprasegmental centers control the threshold and the slope of me tonic stretch reflex. As Kots remembers, that was “no big deal.”

O.G. Meijer is with the Faculty of Human Movement Sciences, Vrije Universiteit, Van der Boechorststraat 9. 1081 BT Amsterdam, The Netherlands <>. Y.M. Kots can be reached at 14567 Dickens Street #119, Sherman Oaks, CA 91403, USA. V.R. Edgerton is with the Department of Physiological Science, and the Department of Neurobiology, Brain Research Institute, University of California Los Angeles, 621 Young Drive, Los Angeles, CA 90095, USA <>.