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Simple Summary: An essential stage in the maturation of the central nervous system and the self-organization of neural circuits occurs during the first year of life. Sensory feedback resulting from interactive and spontaneous movements is instrumental for developing sensorimotor circuits in early infancy, and shorter gestational periods may have an impact on muscle strength and functionality. We examined developmental changes in muscle responses to passive movements and muscle activities during spontaneous movements in preterm and full-term infants by analyzing polymyographic recordings in the lower and upper limb muscles. The major finding of the current study was that there were age-related changes in the manifestation of muscle responses in both preterm and full-term infants. The first six months were the major observational period for the variations in post-term development of muscle activity in preterm infants. Manifestation of muscle reactions at an early developmental stage may reflect the processes underlying the generation of appropriate muscle tone, which is also an integral part of all movements. In preterm infants, some aspects of muscular development may occur differently than in infants born at term. Here we evaluated early manifestations of muscle tone by measuring muscle responses to passive stretching (StR) and shortening (ShR) in both upper and lower limbs in preterm infants (at the corrected age from 0 weeks to 12 months), and compared them to those reported in our previous study on full-term infants. In a subgroup of participants, we also assessed spontaneous muscle activity during episodes of relatively large limb movements. The results showed very frequent StR and ShR, and also responses in muscles not being primarily stretched/shortened, in both preterm and full-term infants. A reduction of sensorimotor responses to muscle lengthening and shortening with age suggests a reduction in excitability and/or the acquisition of functionally appropriate muscle tone during the first year of life. The alterations of responses during passive and active movements in preterm infants were primarily seen in the early months, perhaps reflecting temporal changes in the excitability of the sensorimotor networks. [ABSTRACT FROM AUTHOR]

Robot-assisted body movements are a useful approach for the rehabilitation of motor dysfunction. Various robots based on end-effector or exoskeleton type have been proposed. However, the effect of these robots on brain activity during assistive lower limb movements remains unclear. In this study, we evaluated brain activity results among robot-assisted passive movements, voluntary active movements, and kinesthetic motor imagery. We measured and compared the brain activities of 21 young, healthy individuals during three experimental conditions associated with lower limb movements (active, passive, and imagery conditions) using functional near-infrared spectroscopy (fNIRS). Our results showed that although different brain areas with significant activity were observed among the conditions, the temporal patterns of the activity in each recording channel and the spatial patterns of functional connectivity showed high similarity between robot-assisted passive movements and voluntary active movements. Conversely, the robot-assisted passive movements did not show any similarity to motor imagery. Overall, these findings suggest that the robotic assistive approach is useful for activating not only afferent processes associated with sensory feedback processing but also motor control-related efferent processes. [ABSTRACT FROM AUTHOR]

Normal subjects can completely eliminate resistance upon imposed head-on-trunk rotations when they are asked to relax. It is not, however, clear how neck reflexes to stretch can be voluntarily suppressed. Reflexive responses might be modified by adjusting the gain of the reflex loop through descending control. Theoretically, necessary corrections upon interfering disturbances during coordinated motor performance requiring the interplay of relaxation/activation may be missing if muscle relaxation is taking place exclusively by this mechanism. It has been alternatively proposed that sensory information from the periphery may be allowed to "neutralize" neck reflexes if it is fed back with opposite sign to the structures driving the reflexes. Six healthy subjects were asked to relax while subjected to head-on-trunk rotations generated by a head motor. After any initial resistance had completely subsided, the head was unexpectedly exposed to "ramp-and-hold" perturbations of up to 2-amplitude and 0.7 s duration. Resistance to stretch consistently reappeared thereupon, suggesting that stretch reflex gain had not been set to zero during the previously achieved complete relaxation. Resistance to perturbations under these circumstances was compared with the forces generated when the same ramp-and-hold displacements were delivered unpredictably to the head held stationary. A quantitative model of neck proprioceptive reflexes suppression has been thus constructed. Gain scheduling or "motor set" cannot sufficiently account for the voluntary reflex suppression during slow passive head rotations. Instead, we propose as underlying mechanism, the "neutralization" of the controlling servo by means of continuous feedback tracking displacement and force signals from the periphery. NEW & NOTEWORTHY Head stabilizing neck reflexes can be voluntarily suppressed or activated depending on the task at hand. By applying brief perturbations unexpectedly, both during passive head-on-trunk movements and at rest, we investigated the mechanism of voluntary suppression of resistance to stretch. A physiologically plausible, neuromechanical model of voluntary/reflexive interactions was constructed favoring feedback over reflex gain adjustments. Accordingly, muscle relaxation during imposed head movements is based on sensory feedback similarly to muscle contractions during purposeful movements. [ABSTRACT FROM AUTHOR]

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. We examined the presence and the characteristics of StR and ShR during slow passive cyclic flexion/extension movements (T~3 s) in the hip, knee, ankle, and elbow joints while awake infants were in the supine position. The results showed that most infants demonstrated prominent ShRs in response to passive joint rotations, although the StR was observed more frequently, suggesting that the ShR is an important component of adaptive motor behavior already at an early developmental stage. Interestingly, the occurrence of both StR and ShR in most muscles significantly decreased throughout the first year of life. Passive cyclic flexion/extension movements could also evoke rhythmic muscle responses in other joints or in the contralateral limb, however, such responses were predominantly observed in younger infants (<6 months). A noticeable manifestation of muscle reactions at an early developmental stage, along with spontaneous motor activity in this period of life, may reflect the processes underlying a formation of appropriate muscle tone and the self-organization of neural circuits. A substantial reduction of ipsilateral and contralateral muscle responses to passive movements with age is consistent with the idea of a functional reorganization of the motor circuitry during early development. [ABSTRACT FROM AUTHOR]

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. We examined the presence and the characteristics of StR and ShR during slow passive cyclic flexion/extension movements (T~3 s) in the hip, knee, ankle, and elbow joints while awake infants were in the supine position. The results showed that most infants demonstrated prominent ShRs in response to passive joint rotations, although the StR was observed more frequently, suggesting that the ShR is an important component of adaptive motor behavior already at an early developmental stage. Interestingly, the occurrence of both StR and ShR in most muscles significantly decreased throughout the first year of life. Passive cyclic flexion/extension movements could also evoke rhythmic muscle responses in other joints or in the contralateral limb, however, such responses were predominantly observed in younger infants (<6 months). A noticeable manifestation of muscle reactions at an early developmental stage, along with spontaneous motor activity in this period of life, may reflect the processes underlying a formation of appropriate muscle tone and the self-organization of neural circuits. A substantial reduction of ipsilateral and contralateral muscle responses to passive movements with age is consistent with the idea of a functional reorganization of the motor circuitry during early development. [ABSTRACT FROM AUTHOR]

Previous evidence has shown that tool-use can reshape one's own body schema, extending peripersonal space and modulating the representation of related body parts. Here, we investigated the role of tool action in shaping the body metric representation, by contrasting two different views. According to a first view, the shaping would rely on the mere execution of tool action, while the second view suggests that the shaping induced by tool action on body representation would primarily depend on the representation of the action goals to be accomplished. To this aim, we contrasted a condition in which participants voluntarily accomplish the movement by representing the program and goal of a tool action (i.e., active tool-use training) with a condition in which the tool-use training was produced without any prior goal representation (i.e., passive tool-use training by means of robotic assistance). If the body metric representation primarily depends on the coexistence between goal representation and bodily movements, we would expect an increase of the perceived forearm length in the post- with respect to the pre-training phase after the active training phase only. Healthy participants were asked to estimate the midpoint of their right forearm before and after 20 min of tool-use training. In the active condition, subjects performed "enfold-and-push" movements using a rake to prolong their arm. In the passive condition, subjects were asked to be completely relaxed while the movements were performed with robotic assistance. Results showed a significant increase in the perceived arm length in the post- with respect to the pre-training phase only in the active task. Interestingly, only in the post-training phase, a significant difference was found between active and passive conditions, with a higher perceived arm length in the former than in the latter. From a theoretical perspective, these findings suggest that tool-use may shape body metric representation only when action programs are motorically represented and not merely produced. From a clinical perspective, these results support the use of robots for the rehabilitation of brain-damaged hemiplegic patients, provided that robot assistance during the exercises is present only "as-needed" and that patients' motor representation is actively involved. [ABSTRACT FROM AUTHOR]

The early stages of motor skill acquisition are often marked by uncertainty about the sensory and motor goals of the task, as is the case in learning to speak or learning the feel of a good tennis serve. Herewepresent an experimental model of this early learning process, in which targets are acquired by exploration and reinforcement rather than sensory error. We use this model to investigate the relative contribution of motor and sensory factors to human motor learning. Participants make active reaching movements or matched passive movements to an unseen target using a robot arm. We find that learning through passive movements paired with reinforcement is comparable with learning associated with active movement, both in terms of magnitude and durability, with improvements due to training still observable at a 1 week retest. Motor learning is also accompanied by changes in somatosensory perceptual acuity. No stable changes in motor performance are observed for participants that train, actively or passively, in the absence of reinforcement, or for participants who are given explicit information about target position in the absence of somatosensory experience. These findings indicate that the somatosensory system dominates learning in the early stages of motor skill acquisition. [ABSTRACT FROM AUTHOR]

Further development of an EEG based communication device for patients with disorders of consciousness (DoC) could benefit from addressing the following gaps in knowledge-first, an evaluation of different types of motor imagery; second, an evaluation of passive feet movement as a mean of an initial classifier setup; and third, rapid delivery of biased feedback. To that end we investigated whether complex and/or familiar mental imagery, passive, and attempted feet movement can be reliably detected in patients with DoC using EEG recordings, aiming to provide them with a means of communication. Six patients in a minimally conscious state (MCS) took part in this study. The patients were verbally instructed to perform different mental imagery tasks (sport, navigation), as well as attempted feet movements, to induce distinctive event-related (de)synchronization (ERD/S) patterns in the EEG. Offline classification accuracies above chance level were reached in all three tasks (i.e., attempted feet, sport, and navigation), with motor tasks yielding significant (p < 0.05) results more often than navigation (sport: 10 out of 18 sessions; attempted feet: 7 out of 14 sessions; navigation: 4 out of 12 sessions). The passive feet movements, evaluated in one patient, yielded mixed results: whereas time-frequency analysis revealed task-related EEG changes over neurophysiological plausible cortical areas, the classification results were not significant enough (p < 0.05) to setup an initial classifier for the detection of attempted movements. Concluding, the results presented in this study are consistent with the current state of the art in similar studies, to which we contributed by comparing different types of mental tasks, notably complex motor imagery and attempted feet movements, within patients. Furthermore, we explored new venues, such as an evaluation of passive feet movement as a mean of an initial classifier setup, and rapid delivery of biased feedback. [ABSTRACT FROM AUTHOR]

The degree of activation of the central stepping program during passive leg movement was studied in healthy subjects under unloading conditions; the excitability of spinal motoneurons was studied during passive and voluntary stepping movements. Passive stepping movements with characteristics maximally close to those during voluntary stepping were accomplished by the experimenter. The bursts of muscular activity during voluntary and imposed stepping movements were compared. In addition, the influence on the leg movement of artificially created loading onto the foot was studied. The excitability of spinal motoneurons was estimated by the amplitude of modulation of the m. soleus H reflex. Changes in the H reflex (Hoffmann's reflex) after fixation of the knee and hip joints were also studied. In most subjects, passive movements were accompanied by bursts of electromyographic (EMG) activity in the hip muscles (sometimes in shank muscles); the timing of the EMG burst during the step cycle coincided with the burst's timing during voluntary stepping. In many cases, the bursts in EMG activity exceeded the activity of homonymous muscles during voluntary stepping. Simulation of foot loading influenced significantly the distal part of the moving extremity during both voluntary and passive movements, which was expressed in the appearance of movements in the ankle joint and an increase in the phasic EMG activity of the shank muscles. The excitability of motoneurons during passive movements was higher than during voluntary movements. Changes and modulation of the H reflex throughout the step cycle were similar without restriction of joint mobility and without hip joint mobility. Fixation of the knee joint was of great importance. It is supposed that imposed movements activate the same mechanisms of rhythm generation as supraspinal commands during voluntary movements. During passive movements, presynaptic inhibition depends mostly on the afferent influences from the moving leg rather than on the central commands. Under the conditions of 'air-stepping,' the afferent influences from the foot pressure receptors are likely to interact actively with the central program of stepping and to determine the final activity pattern irrespective of the movement type (voluntary or passive). [ABSTRACT FROM AUTHOR]

In this paper we present an original method to estimate in vivo the joint dynamics of the human limbs. The method is based on a noninvasive and painless technology making use of an optical motion capture system and an associated skeletal model to record the human motion and compute its kinematics and its dynamics. The formalism that is used for the identification is commonly used in robotics. The passive limb joints properties are modeled by enhanced springdamper systems. The inverse dynamics is sampled along a movement to give an over-determined system. The obtained system is solved by the linear least-squares method. To perform the estimation, we place emphasis on giving indicators and requirements to interpret the obtained results, and on using painless, passive constraint-free movements that are usually performed during the clinical diagnosis of neuromuscular diseases. Finally the method is experimentally applied to two healthy subjects and five patients of neuromuscular diseases in order to estimate the upper-limb viscoelastic properties. The obtained results are discussed. [ABSTRACT FROM AUTHOR]

Patients with multiple sclerosis (MS) activate a more diffuse cortical network than do healthy subjects when they perform motor tasks. This brain functional reorganisation might contribute to the limiting of disability, but it is unclear whether there is a loss of regional activation in more advanced disease. The aim of this study was to assess whether functional reorganisation diminishes in more disabled patients with primary progressive (PP) MS. The differences in the fMRI response to active and passive movements of the dominant ankle of 13 patients and 16 controls were assessed. The relationships between functional activation and disability and brain lesion load and atrophy were investigated. Patients showed greater fMRI activation than controls with passive movements in the superior temporal gyrus, rolandic operculum, and putamen. The fMRI response to active and passive movements in the ipsilateral inferior frontal gyrus was lower in patients with greater disability and greater brain T2 lesion load, respectively. Furthermore, the fMRI activation with active movements in the contralateral cerebellum was lower in patients with worse mobility. The increased activity with passive movements in regions that participate in sensori–motor integration, such as the putamen, reflects true functional reorganisation, since passive movements induce brain activation through sensory afferents only. The inverse correlation between the fMRI response in regions that are associated with motor control, and clinical or MRI measures of disease progression, suggests that there is a loss of distributed activation in more disabled patients. This may inform future treatment strategies. [ABSTRACT FROM AUTHOR]

Recovery from hemiplegia is a complex phenomenon that depends on various adaptive processes involving both the affected and the unaffected hemisphere. Our aim in this study was to investigate changes in cerebral perfusion in hemiplegic stroke patients during passive movements and their correlation with the subsequent motor recovery. The study included 30 patients with single, subcortical ischemic cerebral lesions. Within 14 days (range 8 to 14 days) from stroke onset, all patients were examined for the effects of passive elbow movements on cerebral blood flow in the middle cerebral arteries (MCAs) by means of bilateral transcranial Doppler (TCD) ultrasonography. On the same day as TCD assessment, they were also evaluated clinically with the Canadian Neurological Scale (CNS) and with Medical Research Council (MRC) scale for motor deficit of the affected arm. A clinical evaluation using the same scales was repeated after two months of motor rehabilitation therapy. We investigated the relationship between changes of Mean Flow Velocity (MFV) during passive movements and degree of recovery after stroke. The logistic regression procedure indicated that out of all factors considered as possibly related to a good clinical motor deficit recovery of the affected arm, evaluated by means of MRC, only the MFV percentage increase played a predictive role. In particular, for each additional point of contralateral MFV percentage increase during passive movement of the affected arm, the relative probability of good clinical recovery increased 5.68 times (95% CI=1.76–18.40; p=0.004). Similar results were found when the clinical recovery was measured by means of the CNS (slope=0.40, p<0.001). Passive movements in hemiplegic stroke patients before clinical recovery elicit activation patterns that may be critical for the restoration of motor function.I n particular, early and consistent activation of the affected hemisphere, as detected with TCD, seems to predict the positive evolution of a motor deficit. [ABSTRACT FROM AUTHOR]

Transcranial Doppler ultrasonography (TCD) has been widely used to obtain information about changes in cerebral perfusion during monitor activity after stroke. This type of application is greatly limited when severe motor deficits are presnet that impede the performance of an active motor task. In this study, we explored the effect of performing passive arm movements on cerebral perfusion. Twenty healthy subjects were investigated. A bilateral TCD monitoring of the middle cerebral artery (MCA) flow velocity was performed during the following experimental conditions: 1-min of active and passive flexion extension elbow movement and 1-min of active and passive dorsal extension hand movement. Each task was performed with both left and right arms. The percentage increase in flow velocity from rest to task performance was calculated. Each task produced a significantly greater increase in mean flow velocity in the contralateral MCA with respect to the ipsilateral. When comparing the effect of passive and active tasks, no significant difference in mean flow velocity changes recorded in the ipsilateral and the contralateral MCA was detected regarding either elbow or hand movements. These findings demonstrate the possibility of obtaining information about changes in hemispheric cerebral perfusion during passive movements involving elbow and hand. This type of application deserves further attention in the study of cerebral functional changes following cerebral lesions. [ABSTRACT FROM AUTHOR]

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1) Experiments were designed to detect how static parameters of natural, passive hand movements are encoded and integrated within the cerebellar cortex. For this purpose unit activity was recorded extracellularly from presumed mossy fibres (MF), presumed granule cells (GrC) and from Purkinje cells (PC) discharging with simple spikes (SS) and complex spikes (CS). With respect to the PC, our interest was focussed primarily on the SS activity. The recordings were performed in the intermediate part of the cerebellar anterior lobe of decerebrate cats. The animal's forepaw was passively moved around the wrist joint by an electronically controlled device. The movements were exactly reproducible so that peristimulus time histograms of the unit activity could be constructed. 2) At the input level (MF) and at the first level of integration within the cerebellar cortex (GrC), patterns with similar discharge characteristics were found. Such patterns could, to a limited extent, also be detected at the cerebellar output (SS of PC). However, in most cases of SS discharge, patterns were found with weak correlation between the tonic activity and static parameters of the movements. 3) Absolute paw position, amplitude, and duration of movements were found to be related over wide ranges to the activities of MF and GrC. Absolute position is directly encoded by tonic discharge during the low or high holding phases. Beside this, units were found without a correlation between the tonic discharge and the position of the nonmoving paw. However, in these units it was sometimes observed that the information about the momentary position or the information about the mean position was sometimes conveyed exclusively during the proceeding upward or downward movement. Thus, information about static parameters was transmitted only at times when a dynamic parameter (such as velocity) occurred. This type of position information encoding is termed 'indirect mode of transmission'. 4) A specific relationship between SS unit activity of PC and the absolute position of the forepaw or amplitude of the movement could be found primarily by using multiple ramps instead of single ramp movements. This was observed even if both types of ramp movements had the same velocity, individual amplitude, and tested range. However, on multiple ramp movements the paw generally remained for a shorter period at a specific position level as compared to the single ramp movements. 5) Apart from this timing phenomenon, a late movement response was observed, which results in a specific type of position information encoding on multiple ramp functions. 6) These results indicate that static parameters of a passive limb movement are conveyed via the MF input to the cerebellar cortex. Patterns related to these parameters undergo a change within the MF-, GrC-, Parallel fibre-, PC-system. Different modes of encoding these parameters were observed depending primarily on the neuronal niveau within the cerebellar cortex. Tonic discharge related e.g. to limb position was found at MF and GrC level. Such patterns resemble, at least to a certain extent, those obtained from different peripheral receptors. The high tonic SS activity never showed such a strong relationship to static parameters as observed at the input level; static parameters could be resolved only within relatively short periods of time, especially during the dynamic phases of the movement or during short periods immediately following these phases. This implies that the function of this part of the cerebellum, which is to provide correction signals, should be considered as a more dynamic process characterized by evaluating predominantly information about the momentary ongoing movement. [ABSTRACT FROM AUTHOR]

Discharges of Purkinje cells (PCs) with simple (SS) and complex spikes (CS) in the czone of lobule Vc of the anterior lobe of the cerebellar cortex were analyzed in the decerebrate cat during a passive movement of the cat forepaw. The CS of the PC responded differentially and/or proportionally to the position of the extremity, amplitude of the movement, velocity and acceleration. Inphase and outphase responses of the climbing fiber (CF) system to sinusoidal movements could depend on the position of the extremity within the operational range. From these results we deduce that peripheral events can be signalled by the CF system. The possible function of the interaction between the two inputs at the PC level is discussed. [ABSTRACT FROM AUTHOR]