Higher Responsiveness of Pattern Generation Circuitry to Sensory Stimulation in Healthy Humans Is Associated with a Larger Hoffmann Reflex.

The state and excitability of pattern generators are attracting the increasing interest of neurophysiologists and clinicians for understanding the mechanisms of the rhythmogenesis and neuromodulation of the human spinal cord. It has been previously shown that tonic sensory stimulation can elicit non-voluntary stepping-like movements in non-injured subjects when their limbs were placed in a gravity-neutral unloading apparatus. However, large individual differences in responsiveness to such stimuli were observed, so that the effects of sensory neuromodulation manifest only in some of the subjects.

Muscle Responses to Passive Joint Movements in Infants During the First Year of Life.

Muscle tone represents one of the important concepts for characterizing changes in the state of the developing nervous system. It can be manifested in the level of activity of flexors and extensors and in muscle reactions to its passive stretching (StR) or shortening (ShR). Here we investigated such reactions in a cohort of healthy infants aged from 2 weeks to 12 months.

Synergistic influences of sensory and central stimuli on non-voluntary rhythmic arm movements.

In recent years, neuromodulation of the cervical spinal circuitry has become an area of interest for investigating rhythmogenesis of the human spinal cord and interaction between cervical and lumbosacral circuitries, given the involvement of rhythmic arm muscle activity in many locomotor tasks. We have previously shown that arm muscle vibrostimulation can elicit non-voluntary upper limb oscillations in unloading body conditions. Here we investigated the excitability of the cervical spinal circuitry by applying different peripheral and central stimuli in healthy humans.

Electrical Spinal Stimulation, and Imagining of Lower Limb Movements to Modulate Brain-Spinal Connectomes That Control Locomotor-Like Behavior.

Neuronal control of stepping movement in healthy human is based on integration between brain, spinal neuronal networks, and sensory signals. It is generally recognized that there are continuously occurring adjustments in the physiological states of supraspinal centers during all routines movements. For example, visual as well as all other sources of information regarding the subject's environment.

Tonic and Rhythmic Spinal Activity Underlying Locomotion.

In recent years, many researches put significant efforts into understanding and assessing the functional state of the spinal locomotor circuits in humans. Various techniques have been developed to stimulate the spinal cord circuitries, which may include both diffuse and quite specific tuning effects. Overall, the findings indicate that tonic and rhythmic spinal activity control are not separate phenomena but are closely integrated to properly initiate and sustain stepping.

Rhythmic wrist movements facilitate the soleus H-reflex and non-voluntary air-stepping in humans.

Neural coupling between the upper and lower limbs during human walking is supported by modulation of cross-limb reflexes and the presence of rhythmic activity in the proximal arm muscles. Nevertheless, the involvement of distal arm muscles in cyclic movements and sensorimotor neuromodulation is also suggested given their step-synchronized activation in many locomotor-related tasks (e.g.

[Are Interlimb Interactions Disturbed in Patients with Parkinson's Disease: a Study in Unloading Condition?].

During natural human locomotion neural connections characteristic for the control of quadrupedal walking are activated. The degree of interaction between the neural networks generating rhythmic movements of the upper and lower extremities, depends on the tonic state of each of these networks, adjustable by motor command in the brain. The distortion of such command in patients with Parkinson's disease (PD) may lead to disturbance of interlimb interactions.

[The Activation of Interlimb Interactions Increase the Motor Output in Legs in Healthy Subjects under the Conditions of Arm and Leg Unloading].

We studied the effect of arm movements and movements of separate arm joints on the electrophysiological and kinematic characteristics of voluntary and vibration-triggered stepping-like leg movements under the conditions of horizontal support of upper and lower limbs. The horizontal support of arms provided a significantly increase in the rate of activation of locomotor automatism by non-invasive impact on tonic sensory inputs. The addition of active arm movements during involuntary rhytmic stepping-like leg movements led to an increase in EMG activity of hip muscles and was accompanied by an increase in the amplitude of hip and shin movements.

Integration of sensory, spinal, and volitional descending inputs in regulation of human locomotion.

We reported previously that both transcutaneous electrical spinal cord stimulation and direct pressure stimulation of the plantar surfaces of the feet can elicit rhythmic involuntary step-like movements in noninjured subjects with their legs in a gravity-neutral apparatus. The present experiments investigated the convergence of spinal and plantar pressure stimulation and voluntary effort in the activation of locomotor movements in uninjured subjects under full body weight support in a vertical position. For all conditions, leg movements were analyzed using electromyographic (EMG) recordings and optical motion capture of joint kinematics.

Human cervical spinal cord circuitry activated by tonic input can generate rhythmic arm movements.

The coordination between arms and legs during human locomotion shares many features with that in quadrupeds, yet there is limited evidence for the central pattern generator for the upper limbs in humans. Here we investigated whether different types of tonic stimulation, previously used for eliciting stepping-like leg movements, may evoke nonvoluntary rhythmic arm movements. Twenty healthy subjects participated in this study.

Tapping into rhythm generation circuitry in humans during simulated weightlessness conditions.

An ability to produce rhythmic activity is ubiquitous for locomotor pattern generation and modulation. The role that the rhythmogenesis capacity of the spinal cord plays in injured populations has become an area of interest and systematic investigation among researchers in recent years, despite its importance being long recognized by neurophysiologists and clinicians. Given that each individual interneuron, as a rule, receives a broad convergence of various supraspinal and sensory inputs and may contribute to a vast repertoire of motor actions, the importance of assessing the functional state of the spinal locomotor circuits becomes increasingly evident.

[Interlimb interactions during cyclic in-phase and antiphased movements of arms and legs and their dependence on afferent influences].

Coordinated movements of arms and legs suppose the neural interaction between the generators of the rhythmics of the upper and lower extremities. In the lying position in 10 healthy subjects activity of the muscles of the upper and lower extremities was recorded when separate and joint cyclic movements of the arms and legs with different phase relationships between the movements of the limbs were performed, and under various conditions of the motor task. Antiphased active arm movements were characterized by increased muscle activity than during in-phase mode.

Activation of spinal locomotor circuits in the decerebrated cat by spinal epidural and/or intraspinal electrical stimulation.

The present study was designed to further compare the stepping-like movements generated via epidural (ES) and/or intraspinal (IS) stimulation. We examined the ability to generate stepping-like movements in response to ES and/or IS of spinal lumbar segments L1-L7 in decerebrate cats. ES (5-10 Hz) of the dorsal surface of the spinal cord at L3-L7 induced hindlimb stepping-like movements on a moving treadmill belt, but with no rhythmic activity in the forelimbs.

Initiation and modulation of locomotor circuitry output with multisite transcutaneous electrical stimulation of the spinal cord in noninjured humans.

The mammalian lumbar spinal cord has the capability to generate locomotor activity in the absence of input from the brain. Previously, we reported that transcutaneous electrical stimulation of the spinal cord at vertebral level T11 can activate the locomotor circuitry in noninjured subjects when their legs are placed in a gravity-neutral position (Gorodnichev RM, Pivovarova EA, Pukhov A, Moiseev SA, Savokhin AA, Moshonkina TR, Shcherbakova NA, Kilimnik VA, Selionov VA, Kozlovskaia IB, Edgerton VR, Gerasimenko IU. Fiziol Cheloveka 38: 46-56, 2012).

[Investigation of muscle tone in patients with Parkinson's disease in unloading conditions].

Parkinson's disease (PD) is a progressive neurodegenerative disorder, ones of the main symptoms of which are hypertonicity and emergent difficulties during performance of stepping movements due to increased muscle stiffness. Biomechanical (stiffness) and electrophysiological (shorting reaction) characteristics of hip and shank muscles were examined in 25 patients with mild and moderate stages of PD (1 to 3 of Hoehn & Yahr Rating Scale, 61 +/- 9 years) and 22 age-matched healthy controls in unloading leg conditions during passive flexion/extension of hip, knee and ankle joints, as well as the changes of tonic state under levodopa influence. The data obtained were compared with similar findings of healthy subjects.

Effects of transcranial magnetic stimulation during voluntary and non-voluntary stepping movements in humans.

Here, we compared motor evoked potentials (MEP) in response to transcranial magnetic stimulation of the motor cortex and the H-reflex during voluntary and vibration-induced air-stepping movements in humans. Both the MEPs (in mm biceps femoris, rectus femoris and tibialis anterior) and H-reflex (in m soleus) were significantly smaller during vibration-induced cyclic leg movements at matched amplitudes of angular motion and muscle activity. These findings highlight differences between voluntary and non-voluntary activation of the spinal pattern generator circuitry in humans, presumably due to an extra facilitatory effect of voluntary control/triggering of stepping on spinal motoneurons and interneurons.

[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.

Lack of non-voluntary stepping responses in Parkinson's disease.

The majority of research and therapeutic actions in Parkinson's disease (PD) focus on the encephalic areas, however, the potential involvement of the spinal cord in its genesis has received little attention. Here we examined spinal locomotor circuitry activation in patients with PD using various types of central and peripheral tonic stimulation and compared results to those of age-matched controls. Subjects lay on their sides with both legs suspended, allowing low-friction horizontal rotation of the limb joints.

[Abnormalities in mutual influences of upper and lower limbs in patients with stroke].

Previously, in healthy subjects the common pattern of muscle activation and specifics of interlimb neuron connections during performance of rhythmic separate and simultaneous movements of arms and legs in the lying position, which reflect functional meaningful of interlimb interactions, were shown. The aim of this research was to investigate such mutual influences of upper and lower limbs during the execution of similar motor tasks by patients with stroke. In sixteen poststroke patients with different stage of hemiparesis arms movements together with or without legs movements were performed, while lying supine.

[The influence of vibration on spinal alpha-motoneurons excitability in static conditions and during evoked stepping in human].

In healthy human the excitability of spinal alpha-motoneurons under application of vibrostimulation (20-60 Hz) to different leg muscles was investigated both in stationary condition and during stepping movements caused by vibration in the condition of suspended leg. In 15 subjects the amplitude of H-reflex were compared under vibration of rectus femoris (RF) and biceps femoris (BF) muscles of left leg as well during vibration of rectus femoris of contralateral, motionless leg in three spatial positions: upright, supine and on right side of body with suspended left leg. In dynamic conditions the amount of H-reflex was compared during evoked and voluntary stepping at 8 intervals of step cycle.

[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.

[Mutual influences of upper and lower extrimities during cyclic movements].

The possibility of muscle activation of passive arm during its cyclic movements, imposed by active movements of contralateral arm or by experimenter was studied, as well as the influence of lower extremities cyclic movements onto arm muscles activity. In addition to that the activity of legs muscles was estimated in dependence on motor task condition for arms. Ten healthy supine subjects carried out opposite movements of arms with and without stepping-like movements of both legs.

[The influence of afferent inputs from the foot load receptors onto spinal alpha-motoneurons excitability in air-stepping condition].

We investigated excitability of alpha-motoneurons during voluntary and passive locomotor-like movements under air-stepping conditions during the imitation of foot loading. Limb loading notably inhibited the H-reflex during both static condition and active or passive stepping. Thus, load-related afferent inputs play an essentially role in phase-dependence H-reflex modulation.

[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.