ISSN 0362-1197, Human Physiology, 2012, Vol. 38, No. 2, pp. 158–167. © Pleiades Publishing, Inc., 2012. Original Russian Text © R.M. Gorodnichev, E.A. Pivovarova, A. Puhov, S.A. Moiseev, A.A. Savochin, T.R. Moshonkina, N.A. Chsherbakova, V.A. Kilimnik, V.A. Selionov, I.B. Kozlovskaya,V.R. Edgerton, Yu.P. Gerasimenko, 2012, published in Fiziologiya Cheloveka, 2012, Vol. 38, No. 2, pp. 46–56. 158 Neuronal networks formed by the interneurons of the spinal cord that are located in the cervical and lumbar enlargements and are usually called the SPGs play an important role in the regulation of locomotion. Most researchers believe that all mammals, including humans, have SPGs [1–3]. Normally, the activity of SPGs is regulated by brain structures. However, in the case of disorders of the connections between the brain and spinal cord, as a result of traumatic spinal cord lesions, SPGs can be activated by epidural electrical stimulation of the lumbar thickening. It has been shown that epidural electrical spinal cord stimulation (eESCS) can cause electromyographic (EMG) pat- terns in the leg muscles of patients with clinically com- plete spinal cord injury [1, 4, 5]. eESCS is an invasive method and requires surgical implantation of elec- trodes on the dorsal surface of the spinal cord, which confines this method of activating SPGs to clinics. Recently, a noninvasive method for activating the SPGs by means of leg muscle vibration and spinal cord electromagnetic stimulation was suggested. It was found that the vibration of the tendons of the hip mus- cles initiates involuntary walking movements in sub- jects lying on their side with an external support for the legs [6, 7]. In addition, electromagnetic stimulation of the rostral segments of the lumbar spinal cord caused involuntary walking movements in healthy subjects in a similar position with a support for the legs [8, 9]. Steplike movements elicited by vibration and electro- magnetic stimulation, have apparently a different ori- gin. In the former case, the SPG is activated by affer- ent input mainly due to the activation of muscle recep- tors, whereas in the latter case, the neuronal locomotor network is affected directly. Each of these methods has its specificity. For example, the vibratory muscle stimulation elicits involuntary locomotor movements only in the hip and knee joints, without the involvement of the ankle. In addition, these char- acteristic movements could be evoked only in 50% of the subjects [7]. The percentage of subjects in whom the spinal cord electromagnetic stimulation evoked involuntary steplike movements was even smaller (10%), although in this case, the kinematic structure of the resultant movements was consistent with the natural random steplike movements to a greater extent than in the case of vibration [8, 9]. In addition, the spi- nal cord’s electromagnetic stimulation is limited by the technical capabilities of the stimulator. The mod- Transcutaneous Electrical Stimulation of the Spinal Cord: A Noninvasive Tool for the Activation of Stepping Pattern Generators in Humans R. M. Gorodnichev a , E. A. Pivovarova a , A. Puhov a , S. A. Moiseev a , A. A. Savochin b , T. R. Moshonkina b , N. A. Chsherbakova b , V. A. Kilimnik c , V. A. Selionov d , I. B. Kozlovskaya e , V. R. Edgerton f , and Yu. P. Gerasimenko a,f a Velikie Luki State Academy of Physical Education and Sports, Velikie Luki, Pskov oblast, 182100 Russia b Pavlov Institute of Physiology, Russian Academy of Sciences, St. Petersburg, 199034 Russia c St. Petersburg State University of Aerospace Instrumentation, St. Petersburg, 190000 Russia d Kharkevich Institute for Information Transmission Problems, Russian Academy of Sciences, Moscow, 127994, Russia e Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, 123007 Russia f Department of Physiological Science, University of California, 90024 Los Angeles, California, United States Received September 27, 2011 Abstract—A new method for the activation of stepping pattern generators (SPGs) in humans by transcuta- neous electrical spinal cord stimulation (tESCS) has been described. The tESCS applied in the region of the T11–T12 vertebrae with a frequency of 5–40 Hz elicited involuntary steplike movements in healthy subjects with their legs suspended in a gravity-neutral position. The amplitude of evoked steplike movements increased with increasing tESCS frequency. The frequency of evoked steplike movements did not depend on the frequency of tESCS. It was shown that the hip, knee, and ankle joints were involved in the evoked move- ments. It has been suggested that tESCS activates the SPG through the dorsal roots that enter the spinal cord. tESCS can be used as a noninvasive method in rehabilitation of spinal pathology. Keywords: electric stimulation, spinal cord, locomotion. DOI: 10.1134/S0362119712020065