[Galvanic vestibular stimulation in physiological and clinical studies in recent years].

Galvanic vestibular stimulation is a simple, harmless, noninvasive and low-cost research technique. In spite on a long history, it has been recently found popularity as a research tool. At present occurs of its revival as a research and diagnostic tool. Considerable effects of such stimulation for motor, visual, somatosensory, vestibular and cognitive/emotional function as well as for a range of neurological and psychiatric disorders have been reported. Obviously, any process that is able to extract an information due to head acceleration signals is a candidate on galvanic vestibular stimulation. In this review, we describe the basic physiological mechanisms of action of galvanic vestibular stimulation. We also consider a modern data of its influence on human, obtained in physiological and clinical studies.

[Mechanical stimulation of soles' support zones: non-invasive method of activation of generators of stepping movements in man].

The effects of mechanical stimulation of the soles' support zones in regimens of slow and fastwalking (75 and 120 steps per minute) were studied using the model of supportlessness (legs suspension). 20 healthy subjects participated in the study. EMG activity of hip and shin muscles was recorded. Kinematic of leg movements was assessed with the use of videoanalysis system. Support stimulation was followed by leg movements in 80% of cases, in 53% it was a locomotion-like movement. EMG bursts accompanied the movements. Involvement order and alteration of bursts in muscles were similar to voluntary walking. EMG activity occurred with a delay of 5.17 ± 1.08 seconds for hip muscles and 14.01 ± 2.82 seconds for shin muscles, frequency of bursts differed from stimulation frequency. Support stimulation was followed by leg movements in 80% of cases, in 53% of which they had characteristics of locomotions being accompanied by the burst-like electromyographic activities. Involvement order of the leg muscles and organization of antagonistic muscles activities were analogous to that of voluntary walking. The latencies of electromyographic activity in hip muscles composed 5.17 ± 1.083 s and 14.01 ± 2.82 s - for shin muscles, frequency of bursts differed significantly from stimulation frequency. In 31% of cases the electromyographical activity following the stimulation of the soles' support zones was not burst-like. Its amplitude rose smoothly reaching a certain level that was subsequently maintained. Results of the study showed that soles' support zones stimulation in regimen of locomotion can activate a locomotor generator and that effect evoked by this stimulation includes not only rhythmical but also non-rhythmical (probably postural) components of walking.

[Transcutaneous electrical stimulation of the spinal cord: non-invasive tool for activation of locomotor circuitry in human].

A new tool for locomotor circuitry activation in the non-injured human by transcutaneous electrical spinal cord stimulation (tSCS) has been described. We show that continuous tSCS over T11-T12 vertebrae at 5-40 Hz induced involuntary locomotor-like stepping movements in subjects with their legs in a gravity-independent position. The increase of frequency of tSCS from 5 to 30 Hz augmented the amplitude of evoked stepping movements. The duration of cycle period did not depend on frequency of tSCS. During tSCS the hip, knee and ankle joints were involved in the stepping performance. It has been suggested that tSCS activates the locomotor circuitry through the dorsal roots. It appears that tSCS can be used as a non-invasive method in rehabilitation of spinal pathology.

[Novel method for activation of the locomotor circuitry in human].

We examine the possibility for activation of the involuntary locomotion of the lower limbs by spinal electromagnetic stimulation (ES). The subject laid on the left side. The legs are supported in a gravity-neutral position by special mounting that to provide horizontal rotation in the hip, knee and ankle. ES (3 Hz and 1.56 Tesla) at the T11,-T12 vertebrae induced involuntary locomotor-like movements in the legs. The latency from the initiation of ES to the first EMG burst compoused 0.68 +/- 1.0 s and it shortened at increasing of the frequency ES from 3 Hz to 20 Hz. Thus, the spinal ES can unduce the activation of the locomotor movements in human.

[Locomotion induced by epidural stimulation in decerebrate cat after spinal cord injury].

The effect of partial and complete spinal cord injury (Th7-Th8) on locomotor activity evoked by epidural electrical stimulation (L5 segment, stimulation frequency 5 Hz, current strength 80-100 microA) in decerebrate cats has been investigated. It was established that the cutting of dorsal columns did not influence substantially the locomotion. The destruction of the ventral spinal quadrant resulted in the deterioration and instability of the locomotor rhythm. The injury of lateral or medial descending motor systems led to a redistribution of the tone in antagonist muscles. It was found that locomotion can be evoked by epidural stimulation within 20 h after the complete transaction of the spinal cord. The restoration of polysynaptic components in EMG responses correlated with the restoration of the stepping function. The data obtained confirm that the initiation of locomotion under epidural stimulation is caused by direct action on intraspinal systems responsible for locomotion regulation. In the case of intact or partially injured spinal cord, this effect is under the influence of supraspinal motor systems correcting and stabilizing the evoked locomotor pattern.

[Mechanisms of stepping rhythm formation during epidural spinal cord stimulation in decerebrated and spinal cord transected cats].

The mechanisms of stepping pattern formation during epidural spinal cord stimulation in decerebrated and chronically spinal cord transected cats have been investigated. The features of the stepping performance in hindlimb muscles depending on the parameters of epidural stimulation and afferent input were determined. It was shown that, at nonoptimal parameters of stimulation, stepping movements are not induced. In response to the stimulation, reflectory muscle responses are evoked only. Epidural stimulation with optimal parameters induces coordinated stepping movements in hindlimbs with normal rhythm (0.8-1 Hz), which is accompanied by the electromyographic bursting activity of the corresponding muscles. In decerebrated cats, the formation of electromyographic bursts occurs due to the modulation of early responses and the late polysynaptic activity. In chronically spinal cord transected cats, this process is provided mainly by the amplitude modulation of early responses. The formation of the stepping pattern in decerebrated cats with the participation of spinal interneurons responsible for the polysynaptic activity allows one to perform its correction on the basis of the processing of afferent signals. The activation of this system in chronically spinal cord transected cats can be realized by afferent stimulation alone.

[Morphofunctional characteristic of the rat distal spinal cord after its complete experimental section with subsequent treadbun training of the animal].

Motor activity of rats has been studied after complete experimental section of spinal cord at the lower thoracic level. A treadbun training performed one day after the operation has been shown to lead to the appearance of movement of hindlimbs and to restoration of function of support of the body weight. In our opinion, the key moment in initiation of locomotor movements is stimulation of foot. Morphoimmunohistochemical study (detection of nuclear protein of proliferation cells, synaptophysin, and glial fibrillary acid protein) of the lumbar enlargement has allowed revealing reorganization of motoneurons, interneurons, and afferent chain in the distal part of the sectioned spinal cord. In trained animals there are observed the normal structure of motoneurons and the appearance of aggregates of synaptophysin-immunoreactive structures lost after the operation.

[Morpho-functional characterictic of rat lumbar spinal cord enlargement].

Topography and the distribution of synaptophysin-immunoreactive structures were studied in the rat lumbar spinal cord enlargement. Synaptophysin (synaptic vesicle marker) was found in the gray matter of all Rexed laminae around most neurons and in neuropil. Subpial synaptic contacts, that were not described previously, were found in the white matter by immunohistochemistry and their presence was confirmed by electron microscopy. They were localized directly beneath the astrocyte processes, that cover the spinal cord externally. In the dorsal portion of the white matter within the lumbar spinal cord enlargement, the unmyelinated synaptophysin-immunoreactive component of pyramidal tract was detected which included axonal varicosities and synaptic contacts.

[Mathematical modeling of the mechanisms of locomotory pattern formation under epidural spinal cord stimulation with consideration of peripheral feedback].

The mechanisms of nervous regulation of locomotory activity of the spinal cord and participation of afferent peripheral feedback from lower limb muscles in the formation of locomotory patterns were investigated. The set of electromyograms of lower-limb muscle groups recorded in experiments on mesencephalic cats with application of electric epidural stimulations of lumbar segments of the spinal cord is described by a nonlinear dynamic model constructed on the basis of the Van-der-Pol equation with the compelling member. The conditions of occurrence of the regime of self-oscillations were investigated depending on the parameters of external influence. A modified equation was proposed, which takes into account the role of the afferent feedback and delay between the beginning of stimulation and muscle reaction. The conformity of the mathematical model with experimental data was shown, which makes possible its use both for the description of the mechanism of locomotory pattern formation under epidural spinal cord stimulation and the choice of optimum stimulation conditions.

[Characteristics of the pressure center movement under upright posture regulation]. / Osobennosti dvizheniia tsentra davleniia v usloviiakh podderzhaniia vertikal'noi pozy.

The hypothesis was put forward that, along with the regulation of mass center projection, the system of upright posture control stabilizes the deviation of pressure center from the position of the mass center projection. The regularities in the behavior of the trajectories of pressure center and mass center projection were analysed. Experimental evidence was obtained supporting the validity of the hypothesis. The structure of the control system that corresponds to the new understanding of the variables being regulated during the maintenance of vertical posture was considered.

[Generators of walking movements in humans: spinal mechanisms of their activation]. / Generatory shagatel'nykh dvizhenii cheloveka: spinal'nye mekhanizmy ikh aktivatsii.

The paper is focused on spinal generation of walking movements in patients afflicted with loss of supraspinal control consequent to back trauma. The author cites literature on methods of initiation of walking movements with pharmacological and proprioceptive stimulation. On his own experimental investigations with epidural electrical stimulation of the spinal marrow dorsal surface he proves existence of walking generators in the human. There is evidence that the walking pattern in extensors is formed through amplitude modulation of monosynaptic reflexes, whereas in flexors it is established through switching of the reflex paths from the monosynaptic reflex to the polysynaptic neuron network. Investigations of the functional deafferentation of lower extremities showed that walking movements as a result of epidural stimulation are intraspinal by origin and adjusted by way of peripheral feedback. A hypothetical sequence of activation of walking generators through the propriospinal system of dorsolateral and ventrilateral funiculi has been put forward.

[Diagnosis and treatment of embryonal hernia]. / Diagnostika i lechenie émbrional'noi gryzhi.

In 1994-1999 years in clinic 19 children with omphalocele were treated, 8 of them died. Authors proposed tactic of treatment of their own, giving preference to conservative method, what permitted to reduce mortality of children with embryonal hernia.

[Vestibular influences on human locomotion: results obtained using galvanic vestibular stimulation].

Locomotion is the most important mode of our movement in space. The role of the vestibular system during human locomotion is not well studied, mainly due to problems associated with its isolation stimulation. It is difficult to stimulate this system in isolation during locomotion because the real movement of the head to activate the vestibular end-organs inevitably leads to the activation of other sensory inputs. Galvanic stimulation is not a natural way to stimulate the vestibular system, but it has the advantage providing an isolated stimulation of the vestibular inputs. This technique is relatively novel in the examination of vestibular contributions during human locomotion. In our review we consider the current data regarding the effect of vestibular signals on human locomotion by using galvanic vestibular stimulation.

[Neuronal control of posture and locomotion in decerebrated and spinalized animals].

We have found that the brainstem-spinal cord circuitry of decerebrated cats actively maintain the equilibrium during standing, walking and imposed mechanical perturbations similar to that observed in intact animals. The corrective hindlimb motor responses during standing included redistribution of the extensor activity ipsilateral and contralateral to perturbation. The postural corrections in walking cats were due to considerable modification of EMG pattern in the limbs as well as changing of the swing-stance phases of the step cycle and ground reaction forces depending of perturbation side. Thus the basic mechanisms for balance control of decerebrated animals in these two forms of motor behavior are different. Balance-related adjustments relied entirely on the integration of somatosensory information arising from the moving hindquarters because of the suppression of vestibular, visual, and head-neck-trunk sensory input. We propose that the somatosensory input from the hindquarters in concert with the lumbosacral spinal circuitry can control the dynamics of the hindquarters sufficient to sustain balance. We found that, after isolation from the brainstem or forebrain, lumbosacral circuits receiving tonic epidural electrical stimulation can effectively control equilibrium during standing and stepping. Detailed analyses of the relationships among muscle activity, trunk kinematics, and limb kinetics indicate that spinal motor systems utilize a combination of feedback and feedforward strategies to maintain dynamic equilibrium during walking. The unexpected ability of spinal circuitries to exert efficient postural control in the presence of epidural electrical stimulation in decerebrated and spinal cats have significant implications for the potential of humans with a severe spinal cord injury to regain a significant level of functional standing and walking capacities.

[Analysis of locomotor activity in decerebrated cats during electromagnetic and epidural electrical spinal cord stimulation].

It was shown that the epidural and the electromagnetic tonic stimulation with frequency 5 Hz applied to the lumbal as well as to the cervical region of the spinal cord enabled stepping on a moving treadmill belt in decerebrated cats. It was found that there were differences in initiation of the stepping movements during epidural and electromagnetic stimulation depending on the region of spinal cord stimulation. Stimulation at frequency of 0.3 Hz induced single reflex responses in the anterior and posterior limbs. On the basis of analysis of the response structure it was concluded that the locomotor ability during epidural and electromagnetic stimulation depended on the degree of polysynaptic pathways activation. The hypothesis about stepping pattern generator activation through the dorsal roots during epidural stimulation and more direct activation of neuronal locomotor networks in the case of electromagnetic spinal cord stimulation is discussed.

[Serotoninergic system morphofunctional aspects in control of postural and locomotion function].

Different mediator systems including serotoninergic one can influence animal's locomotor behavior. It has been shown that the spinal cord in the absence of supraspinal control is able to induce the locomotor activity in hindlimbs and afferent system can activate this mechanism. In behavioral studies on the rats with complete transection of the spinal cord it has been demonstrated that the pharmacological blocking of serotoninergic system results in depression of motor activity mediated by activation of support reactions. Histological studies did not reveal any effects of activation of support reactions on the safety of neurons as well as on the distribution of synaptic contacts within L2-L4 spinal segments. At the same time it has been shown that blockade of the serotoninergic system results in alterations of cells located in 1-3 laminae of dorsal horns, and in 7 Rexed's lamina as well as in redistribution of synaptic contacts in 1-4 Rexed laminae of the spinal cord dorsal horns.

[Initiation of locomotion in decerebrated cat by using of impulse magnetic field projected onto the spinal cord segments].

The motor effects induced by impulse magnetic field (IMF) applied to lumbar as well as to cervical enlargements in decerebrated cat were studied. The magnetic coil with diameter 8 cm was placed on the distance 1-2 cm over the spinal cord. Single magnetic spinal cord stimulation with intensity 0.5-1 Tesla as well as continuous magnetic stimulation with frequency of 1 Hz and intensity 0.5 Tesla was performed. Single magnetic stimulation of lumbar enlargement elicited reflex responses in proximal and distal hind limb muscles. Continuous stimulation induced the locomotor activity in hind limbs on moving treadmill belt by activation of neuronal spinal locomotor networks (generator of stepping movements). The stimulation of lumbar enlargement involved into the locomotor activity only hind limbs. Continuous magnetic stimulation of cervical enlargerment evoked coordinated stepping movements in fore- and hind limbs. Initially stepping movements raised in hind limbs and then in forelimbs. After cessation of magnetic stimulation some coordinated stepping movements were observed. Thus, for the first time we showed a possibility to induce the locomotor activity in decerebrated cat by magnetic stimulation. The obtained results demonstrate the ability of non-invasive mode of neuronal spinal locomotor network activation. This approach opens new perspectives for using magnetic stimulation in clinical practice.

[The role of skin afferent in regulation of locomotion evoked by electrical epidural stimulation of spinal cord in decerebrated cats].

The role of hindpaw skin afferent input in the locomotor pattern formation induced by epidural spinal cord stimulation was investigated in decerebrated cats. Locomotor activity was evoked by continuous 3-5Hz stimulation of dorsal surface of L4-L5 spinal segments. Kinematic and electromyographic activity (EMG) of m. Quadriceps, m. Semitendinosus, m. Tibialis anterior an m. Gastrocnemius lateralis before and after blocking of skin receptors in one hind limb were recorded. In addition, reflex responses in the hind limb muscles to epidural stimulation with frequency 0.5 Hz were analysed. Blocking of skin receptors of the foot with chlorothane paw irrigation or 2 % lidocaine administrated into the hind paw was performed. After blocking of skin receptors of the foot the stepping pattern changed. Stepping with dorsal foot placement and dragging during swing phase was observed. Duration of stance phase significantly decreased. Inhibition of polysynaptic activity of proximal and distal extensor muscles and distal flexor muscles of hind paw during locomotion was found. Monosynaptic responses after blocking of skin receptors of the foot changed insignificantly.