Control Of Voluntary Movements Research Articles

Transcranial Direct Current Stimulation on Parietal Operculum Contralateral to the Moving Limb Does Not Affect the Programming of Intra-Limb Anticipatory Postural Adjustments.

Recent data suggest that the parietal operculum acts as an integration center within a multimodal network, originating from different primary sensory and motor cortices and projecting to frontal, parietal and temporal cortical hubs, which in turn govern cognitive and motor functions. Thus, parietal operculum might also play a crucial role in the integrated control of voluntary movement and posture. As a first step to test this hypothesis, the Anticipatory Postural Adjustments (APAs) stabilizing the arm when the index-finger is briskly flexed were recorded, on the preferred side, in three groups of 10 healthy subjects, before, during and after CATHODAL or ANODAL transcranial Direct Current Stimulation (tDCS, 20 min at 2 mA) applied over the contralateral Parietal Operculum (coPO). Results were compared to those obtained in a SHAM group. In agreement with literature, in the SHAM group the activation of the prime mover Flexor Digitorum Superficialis was preceded by an inhibitory APA in Biceps Brachii and Anterior Deltoid, and almost simultaneous to an excitatory APA in Triceps Brachii. The same pattern was observed in both the CATHODAL and ANODAL groups, with no significant tDCS effects on APAs amplitude and timing. Index-finger kinematics were also unchanged. These negative results suggest that the coPO does not disturb the key network governing APAs in index-finger flexion. Since it has been well documented that such APAs share many features with those observed in trunk and limb muscles when performing several other movements, we suggest that coPO may not be crucial to the general APA control.

Artificial Intelligence and Cerebellar Motor Learning

Half a century ago, cerebellar learning models based on a simple perceptron were proposed independently by Marr and Albus. Soon, these models were combined with Ito's flocculus hypothesis that the cerebellar flocculus controls the vestibulo-ocular reflex through teacher signal-dependent learning, and consequently integrated into the so-called Marr-Albus-Ito cerebellar learning hypothesis. Ten years later, Ito found the synaptic plasticity of long-term depression at cerebellar Purkinje cell synapses, which underlies cerebellar learning. The liquid-state machine (LSM) model, which adds the random inhibitory recurrent neural network composed of granule cells --Golgi cells loop to a simple perceptron, explained the learning of timing in eyeblink conditioning, the learning of gains in ocular reflex, and the formation of short- and long-term motor memories in the cerebellum. The LSM model is now extended to the cerebellar internal model-based voluntary movement control and cognitive function. Artificial intelligence (AI) based on the neural network models originating from a simple perceptron, has now developed to deep learning. As the LSM model of the cerebellum is the counterpart of deep learning in the brain, the cerebellum is considered to be the origin of current AI. Finally, we discuss the impact of the evolution of AI on future clinical cerebellar neurology.

The effects of the watsu method on functional capacity, anxiety and depression in patients with parkinson disease

Parkinson's disease (PD) is a chronic and progressive pathology that results from the degeneration of the black substance responsible for the voluntary control of movements. The reduction of dopamine generates motor and non-motor symptoms that hinder the mobility of the patient and the execution of their activities of daily living. The Watsu method relieves pain, tension and releases the muscles, fascias and spine leading to the gain of flexibility and range of motion, and can be a facilitator in reducing the symptoms of PD. The aim was to evaluate the effects of the Watsu method on motor and non-motor symptoms and their relation with the functional capacity of these individuals. This is an experimental study applied to 4 male patients diagnosed with PD. The analyzed variables were: anxiety, depression, quality of life, basic and instrumental activities of daily living and balance. 9 Watsu sessions was applied. Student's t-test (paired sample) was carried out to compare the variables studied. There was no significant improvement in the variables analyzed, but there was a tendency for improvement in quality of life variables (before 38.75 and later 36.50), depression (before 23 and after 21.25) and instrumental activities of daily living (before 19.50 and later 20.75). For the variables anxiety, basic activities of daily living and balance there was no improvement of these variables. It was observed that the Watsu method trends to improve motor and no-motor symptoms that affect the PD patients. In addition, there is still a lack in the literature in studies that use the Watsu method as a treatment for both PD and other diseases.

The impact of evoked cutaneous afferents on voluntary reaching movement in patients with Parkinson’s disease

Objective. Resting tremor may compound the effects of bradykinesia to further prolong the initiation of voluntary movement in patients with Parkinson’s disease (PD). However, the interaction between resting tremor and voluntary movements in these PD patients has not been well understood. Recently, we demonstrated that cutaneous afferents evoked by surface stimulation of superficial radial nerve can inhibit resting tremor effectively. The inhibition appears to take effect via spinal interneuronal pathways. This study evaluates how evoked cutaneous afferents would impact the performance of voluntary movements in PD subjects when tremor is inhibited. Approach. Ten PD patients with tremor and eight age-matched control subjects were recruited to participate in this study. Both groups of subjects performed fast reaching movements, while cutaneous stimulation was delivered during reaching tasks on or off randomly. Kinematic performance, such as reaction time (RT), movement time (MT), and movement variability, as well as muscle synergy of tasks were evaluated and compared to assess the impact of evoked cutaneous afferents on movement performances. Main results. Results indicated that the cutaneous stimulation significantly reduced RT in PD patients by 17.7%; but had an insignificant effect on RT in control subjects. Cutaneous stimulation, however, caused a significantly longer MT both in control subjects (8.6%) and in PD subjects (15.7%). Movement variability was not significantly altered in both groups of subjects by the cutaneous stimulation. Muscle synergy analysis revealed that cutaneous stimulation affected the power spectral densities (PSD) of time profiles of muscle synergies more significantly than the vector patterns of synergies in both control subjects and PD subjects. Significance. These findings provide evidence that tremor increases the RT of voluntary motor control in PD patients, and demonstrate that cutaneous stimulation reduces the RT of voluntary movements significantly, in addition to suppressing tremor, yet without interrupting voluntary control of movements.

Fear conditioning and extinction induce opposing changes in dendritic spine remodeling and somatic activity of layer 5 pyramidal neurons in the mouse motor cortex

Multiple brain regions including the amygdala and prefrontal cortex are crucial for modulating fear conditioning and extinction. The primary motor cortex is known to participate in the planning, control, and execution of voluntary movements. Whether and how the primary motor cortex is involved in modulating freezing responses related to fear conditioning and extinction remains unclear. Here we show that inactivation of the mouse primary motor cortex impairs both the acquisition and extinction of freezing responses induced by auditory-cued fear conditioning. Fear conditioning significantly increases the elimination of dendritic spines on apical dendrites of layer 5 pyramidal neurons in the motor cortex. These eliminated spines are further apart from each other than expected from random distribution along dendrites. On the other hand, fear extinction causes the formation of new spines that are located near the site of spines eliminated previously after fear conditioning. We further show that fear conditioning decreases and fear extinction increases somatic activities of layer 5 pyramidal neurons in the motor cortex respectively. Taken together, these findings indicate fear conditioning and extinction induce opposing changes in synaptic connections and somatic activities of layer 5 pyramidal neurons in the primary motor cortex, a cortical region important for the acquisition and extinction of auditory-cued conditioned freezing responses.

Dopamine neuronal protection in the mouse Substantia nigra by GHSR is independent of electric activity

ObjectiveDopamine neurons in the Substantia nigra (SN) play crucial roles in control of voluntary movement. Extensive degeneration of this neuronal population is the cause of Parkinson's disease (PD). Many factors have been linked to SN DA neuronal survival, including neuronal pacemaker activity (responsible for maintaining basal firing and DA tone) and mitochondrial function. Dln-101, a naturally occurring splice variant of the human ghrelin gene, targets the ghrelin receptor (GHSR) present in the SN DA cells. Ghrelin activation of GHSR has been shown to protect SN DA neurons against 1-methyl-4-phenyl-1,2,5,6 tetrahydropyridine (MPTP) treatment. We decided to compare the actions of Dln-101 with ghrelin and identify the mechanisms associated with neuronal survival. MethodsHistologial, biochemical, and behavioral parameters were used to evaluate neuroprotection. Inflammation and redox balance of SN DA cells were evaluated using histologial and real-time PCR analysis. Designer Receptors Exclusively Activated by Designer Drugs (DREADD) technology was used to modulate SN DA neuron electrical activity and associated survival. Mitochondrial dynamics in SN DA cells was evaluated using electron microscopy data. ResultsHere, we report that the human isoform displays an equivalent neuroprotective factor. However, while exogenous administration of mouse ghrelin electrically activates SN DA neurons increasing dopamine output, as well as locomotion, the human isoform significantly suppressed dopamine output, with an associated decrease in animal motor behavior. Investigating the mechanisms by which GHSR mediates neuroprotection, we found that dopamine cell-selective control of electrical activity is neither sufficient nor necessary to promote SN DA neuron survival, including that associated with GHSR activation. We found that Dln101 pre-treatment diminished MPTP-induced mitochondrial aberrations in SN DA neurons and that the effect of Dln101 to protect dopamine cells was dependent on mitofusin 2, a protein involved in the process of mitochondrial fusion and tethering of the mitochondria to the endoplasmic reticulum. ConclusionsTaken together, these observations unmasked a complex role of GHSR in dopamine neuronal protection independent on electric activity of these cells and revealed a crucial role for mitochondrial dynamics in some aspects of this process.

Evidence Transcranial Direct Current Stimulation Can Improve Saccadic Eye Movement Control in Older Adults.

Objectives: Ageing is associated with declines in voluntary eye movement control, which negatively impact the performance of daily activities. Therapies treating saccadic eye movement control deficits are currently lacking. To address the need for an effective therapy to treat age-related deficits in saccadic eye movement control, the current study investigated whether saccadic behaviour in older adults can be improved by anodal transcranial direct current stimulation (tDCS) over the dorsolateral prefrontal cortex using a montage that has been proven to be effective at improving nonoculomotor control functions. Method: The tDCS protocol entailed a 5 cm × 7 cm anodal electrode and an encephalic cathodal reference electrode positioned over the contralateral supraorbital area. In two experiments, healthy older men completed one active (1.5 mA current for 10 min) and one sham stimulation session, with the session order counterbalanced across participants, and eye movement testing following stimulation. In the first experiment, participants rested during the tDCS (offline), whereas in the follow-up experiment, participants engaged in antisaccades during the tDCS (online). Results: Analyses revealed improvements in saccadic performance following active anodal tDCS relative to sham stimulation in the online experiment, but not in the offline experiment, which was presumably due to the activation of the relevant networks during tDCS promoting more targeted effects. Discussion: These outcomes converge with findings pertaining to nonoculomotor cognitive functions, and provide evidence that tDCS can improve saccadic eye movement control in older adults.

Sensory attenuation in Parkinson\u2019s disease is related to disease severity and dopamine dose

Abnormal initiation and control of voluntary movements are among the principal manifestations of Parkinson’s disease (PD). However, the processes underlying these abnormalities and their potential remediation by dopamine treatment remain poorly understood. Normally, movements depend on the integration of sensory information with the predicted consequences of action. This integration leads to a suppression in the intensity of predicted sensations, reflected in a ‘sensory attenuation’. We examined this integration process and its relation to dopamine in PD, by measuring sensory attenuation. Patients with idiopathic PD (n = 18) and population-derived controls (n = 175) matched a set of target forces applied to their left index finger by a torque motor. To match the force, participants either pressed with their right index finger (‘Direct’ condition) or moved a knob that controlled a motor through a linear potentiometer (‘Slider’ condition). We found that despite changes in sensitivity to different forces, overall sensory attenuation did not differ between medicated PD patients and controls. Importantly, the degree of attenuation was negatively related to PD motor severity but positively related to individual patient dopamine dose, as measured by levodopa dose equivalent. The results suggest that dopamine could regulate the integration of sensorimotor prediction with sensory information to facilitate the control of voluntary movements.

Measurement properties of the upright motor control test in adults with subacute stroke

ABSTRACTBackground: Previous studies have distilled the Upright Motor Control Test Knee Extension and Knee Flexion subscales (UMCT-KE and UMCT-KF, respectively) from the original 6-item instrument and examined these as stand-alone rapid tests of voluntary movement control in the standing position. Systematic review evidence suggests that the UMCT-KE and UMCT-KF may have value in predicting walking ability after stroke.Objective: To examine the interrater and intrarater reliability, and concurrent validity of the UMCT-KE and UMCT-KF, and associations with walking ability in adults with subacute stroke.Methods: A prospective repeated assessments design was implemented in a rehabilitation department in a public teaching hospital. A consecutive sample of patients with subacute first-time stroke (N = 50; mean age = 51 ± 12 years; 20 females; mean time post-stroke = 68 ± 48 days) completed the study. Three physical therapists independently administered the UMCT-KE and UMCT-KF on two testing occasions 2 days apart (t1 and t2). On t2, a fourth rater administered the Leg subscale of the Motricity Index (MI-Leg) as criterion standard.Results: The UMCT-KE and UMCT-KF demonstrated substantial to almost perfect interrater and intrarater reliability (W = 0.77–0.95), with lower limits of 95% confidence intervals extending to no lower than the substantial level. Both the UMCT-KE and UMCT-KF showed high correlations with the MI-Leg (ρ = 0.747–0.775) and significant associations with walking ability. p Values for all tests were <0.001.Conclusions: The UMCT-KE and UMCT-KF are reliable and valid tests for rapidly estimating voluntary movement control of the lower limbs in adults with subacute stroke.

Ipsilesional Motor Cortex Plasticity Participates in Spontaneous Hindlimb Recovery after Lateral Hemisection of the Thoracic Spinal Cord in the Rat.

After an incomplete spinal cord injury (SCI) spontaneous motor recovery can occur in mammals, but the underlying neural substrates remain poorly understood. The motor cortex is crucial for skilled motor learning and the voluntary control of movement and is known to reorganize after cortical injury to promote recovery. Motor cortex plasticity has also been shown to parallel the recovery of forelimb function after cervical SCI, but whether cortical plasticity participates in hindlimb recovery after SCI remains unresolved. Using intracortical microstimulation (ICMS) mapping, behavioral and cortical inactivation techniques in the female Long-Evans rat, we evaluated the spontaneous cortical mechanisms of hindlimb motor recovery 1-5 weeks after lateral hemisection of the thoracic (T8) spinal cord that ablated the crossed corticospinal tract (CST) from the contralesional motor cortex while sparing the majority of the CST from the ipsilesional motor cortex. Hemisection initially impaired hindlimb motor function bilaterally but significant recovery occurred during the first 3 weeks. ICMS revealed time-dependent changes in motor cortex organization, characterized by a chronic abolishment of hindlimb motor representation in the contralesional motor cortex and the development of transient bilateral hindlimb representation in the ipsilesional motor cortex 3 weeks after hemisection, when significant behavioral recovery occurred. Consistently, reversible inactivation of the ipsilesional, but not the contralesional motor cortex, during skilled ladder walking 3 weeks after hemisection reinstated deficits in both hindlimbs. These findings indicate that the ipsilesional motor cortex transiently reorganizes after lateral hemisection of the thoracic spinal cord to support recovery of hindlimb motor function.SIGNIFICANCE STATEMENT Partial motor recovery can occur after an incomplete spinal cord injury and is hypothesized to result from the reorganization of spared descending motor pathways. The motor cortex is crucial for the control of voluntary movement and contains topographical movement representations (motor maps) that are highly plastic. We examined the organization of hindlimb motor maps bilaterally after a lateral hemisection of the spinal cord to show that while motor maps are abolished in the deefferented cortex, the spared ipsilesional cortex transiently reorganizes to gain a representation of the affected hindlimb after injury that relates to recovery. This finding demonstrates that plasticity in the ipsilesional motor cortex at early time points after spinal cord hemisection is initially important to support motor recovery.

Visual salience of the stop signal affects the neuronal dynamics of controlled inhibition

The voluntary control of movement is often tested by using the countermanding, or stop-signal task that sporadically requires the suppression of a movement in response to an incoming stop-signal. Neurophysiological recordings in monkeys engaged in the countermanding task have shown that dorsal premotor cortex (PMd) is implicated in movement control. An open question is whether and how the perceptual demands inherent the stop-signal affects inhibitory performance and their underlying neuronal correlates. To this aim we recorded multi-unit activity (MUA) from the PMd of two male monkeys performing a countermanding task in which the salience of the stop-signals was modulated. Consistently to what has been observed in humans, we found that less salient stimuli worsened the inhibitory performance. At the neuronal level, these behavioral results were subtended by the following modulations: when the stop-signal was not noticeable compared to the salient condition the preparatory neuronal activity in PMd started to be affected later and with a less sharp dynamic. This neuronal pattern is probably the consequence of a less efficient inhibitory command useful to interrupt the neural dynamic that supports movement generation in PMd.

StartReact during gait initiation reveals differential control of muscle activation and inhibition in patients with corticospinal degeneration

Corticospinal lesions cause impairments in voluntary motor control. Recent findings suggest that some degree of voluntary control may be taken over by a compensatory pathway involving the reticulospinal tract. In humans, evidence for this notion mainly comes from StartReact studies. StartReact is the acceleration of reaction times by a startling acoustic stimulus (SAS) simultaneously presented with the imperative stimulus. As previous StartReact studies mainly focused on isolated single-joint movements, the question remains whether the reticulospinal tract can also be utilized for controlling whole-body movements. To investigate reticulospinal control, we applied the StartReact paradigm during gait initiation in 12 healthy controls and 12 patients with ‘pure’ hereditary spastic paraplegia (HSP; i.e., retrograde axonal degeneration of corticospinal tract). Participants performed three consecutive steps in response to an imperative visual stimulus. In 25% of 16 trials a SAS was applied. We determined reaction times of muscle (de)activation, anticipatory postural adjustments (APA) and steps. Without SAS, we observed an overall delay in HSP patients compared to controls. Administration of the SAS accelerated tibialis anterior and rectus femoris onsets in both groups, but more so in HSP patients, resulting in (near-)normal latencies. Soleus offsets were accelerated in controls, but not in HSP patients. The SAS also accelerated APA and step reaction times in both groups, yet these did not normalize in the HSP patients. The reticulospinal tract is able to play a compensatory role in voluntary control of whole-body movements, but seems to lack the capacity to inhibit task-inappropriate muscle activity in patients with corticospinal lesions.

Muscle Synergies Obtained from Comprehensive Mapping of the Cortical Forelimb Representation Using Stimulus Triggered Averaging of EMG Activity

Neuromuscular control of voluntary movement may be simplified using muscle synergies similar to those found using non-negative matrix factorization. We recently identified synergies in electromyography (EMG) recordings associated with both voluntary movement and movement evoked by high-frequency long-duration intracortical microstimulation applied to the forelimb representation of the primary motor cortex (M1). The goal of this study was to use stimulus-triggered averaging (StTA) of EMG activity to investigate the synergy profiles and weighting coefficients associated with poststimulus facilitation, as synergies may be hard-wired into elemental cortical output modules and revealed by StTA. We applied StTA at low (LOW, ∼15 μA) and high intensities (HIGH, ∼110 μA) to 247 cortical locations of the M1 forelimb region in two male rhesus macaques while recording the EMG of 24 forelimb muscles. Our results show that 10-11 synergies accounted for 90% of the variation in poststimulus EMG facilitation peaks from the LOW-intensity StTA dataset while only 4-5 synergies were needed for the HIGH-intensity dataset. Synergies were similar across monkeys and current intensities. Most synergy profiles strongly activated only one or two muscles; all joints were represented and most, but not all, joint directions of motion were represented. Cortical maps of the synergy weighting coefficients suggest only a weak organization. StTA of M1 resulted in highly diverse muscle activations, suggestive of the limiting condition of requiring a synergy for each muscle to account for the patterns observed.SIGNIFICANCE STATEMENT Coordination of muscle activity and the neural origin of potential muscle synergies remains a fundamental question of neuroscience. We previously demonstrated that high-frequency long-duration intracortical microstimulation-evoked synergies were unrelated to voluntary movement synergies and were not clearly organized in the cortex. Here we present stimulus-triggered averaging facilitation-related muscle synergies, suggesting that when fundamental cortical output modules are activated, synergies approach the limit of single-muscle control. Thus, we conclude that if the CNS controls movement via linear synergies, those synergies are unlikely to be called from M1. This information is critical for understanding neural control of movement and the development of brain-machine interfaces.

Polymorphism of the DRD2 Gene in a Mexican Population with Mental Deviations

The important functions of dopamine (DA) in emotional behavior, control of voluntary movements, memory, and attention have been recognized. To date, the 939 C/T (rs6275) polymorphism of this gene has been implicated in association with alcohol and drug abuse and also with schizophrenia. We examined the allele frequencies of 939CT (rs6275) polymorphism of the DRD2 gene and those of the respective genotypes in a Mexican population (n = 166) with mental deviations and a history of suicide attempts and psychiatric diagnoses (101 suicidal individuals from Mexico City and 65 patients recruited from psychiatry outpatients of Tabasco, Mexico). The most common allele found in both subpopulations was the T allele (about 60% and 69%, respectively). In addition to the Mexican population, the frequencies were compared with those in some Asian and American populations. Thus, a noticeable difference of the distribution of the 939 C/T (rs6275) was observed in patients with the above-mentioned mental deviations, as well as in the Asian population with a diagnosis of schizophrenia. Future studies are necessary to evaluate mentally unhealthy populations to observe the role of the above polymorphism in the susceptibility to psychiatric diseases.

Repeated Bout Rate Enhancement Is Elicited by Various Forms of Finger Tapping.

Voluntary rhythmic movements, such as, for example, locomotion and other cyclic tasks, are fundamental during everyday life. Patients with impaired neural or motor function often take part in rehabilitation programs, which include rhythmic movements. Therefore, it is imperative to have the best possible understanding of control and behaviour of human voluntary rhythmic movements. A behavioural phenomenon termed repeated bout rate enhancement has been established as an increase of the freely chosen index finger tapping frequency during the second of two consecutive tapping bouts. The present study investigated whether the phenomenon would be elicited when the first bout consisted of imposed passive finger tapping or air tapping. These two forms of tapping were applied since they can be performed without descending drive (passive tapping) and without afferent feedback related to impact (air tapping) – as compared to tapping on a surface. Healthy individuals (n = 33) performed 3-min tapping bouts separated by 10 min rest. Surface electromyographic, kinetic, and kinematic data were recorded. Supportive experiments were made to measure, for example, the cortical sensory evoked potential (SEP) response during the three different forms of tapping. Results showed that tapping frequencies in the second of two consecutive bouts increased by 12.9 ± 14.8% (p < 0.001), 9.9 ± 6.0% (p = 0.001), and 16.8 ± 13.6% (p = 0.005) when the first bout had consisted of tapping, passive tapping, and air tapping, respectively. Rate enhancement occurred without increase in muscle activation. Besides, the rate enhancements occurred despite that tapping, as compared with passive tapping and air tapping, resulted in different cortical SEP responses. Based on the present findings, it can be suggested that sensory feedback in an initial bout increases the excitability of the spinal central pattern generators involved in finger tapping. This can eventually explain the phenomenon of repeated bout rate enhancement seen after a consecutive bout of finger tapping.

Feedback Control of Functional Electrical Stimulation for 2-D Arm Reaching Movements.

Functional electrical stimulation (FES) can be used as a neuroprosthesis in which muscles are stimulated by electrical pulses to compensate for the loss of voluntary movement control. Modulating the stimulation intensities to reliably generate movements is a challenging control problem. This paper introduces a feedback controller for a multi-muscle FES system to control hand movements in a 2-D (table-top) task space. This feedback controller is based on a recent human motor control model, which uses muscle synergies to simplify its calculations and improve the performance. This synergy-based controller employs direct relations between the muscle synergies and the produced hand force, therefore allowing for the real-time calculation of six muscle stimulation levels required to reach an arbitrary target. The experimental results show that this control scheme can perform arbitrary point-to-point reaching tasks in the 2-D task space in real time, with an average of ~2 cm final hand position error from the specified targets. The success of this prototype demonstrates the potential of the proposed method for the feedback control of functional tasks with FES.

Posture Control-Human-Inspired Approaches for Humanoid Robot Benchmarking: Conceptualizing Tests, Protocols and Analyses.

Posture control is indispensable for both humans and humanoid robots, which becomes especially evident when performing sensorimotor tasks such as moving on compliant terrain or interacting with the environment. Posture control is therefore targeted in recent proposals of robot benchmarking in order to advance their development. This Methods article suggests corresponding robot tests of standing balance, drawing inspirations from the human sensorimotor system and presenting examples from robot experiments. To account for a considerable technical and algorithmic diversity among robots, we focus in our tests on basic posture control mechanisms, which provide humans with an impressive postural versatility and robustness. Specifically, we focus on the mechanically challenging balancing of the whole body above the feet in the sagittal plane around the ankle joints in concert with the upper body balancing around the hip joints. The suggested tests target three key issues of human balancing, which appear equally relevant for humanoid bipeds: (1) four basic physical disturbances (support surface (SS) tilt and translation, field and contact forces) may affect the balancing in any given degree of freedom (DoF). Targeting these disturbances allows us to abstract from the manifold of possible behavioral tasks. (2) Posture control interacts in a conflict-free way with the control of voluntary movements for undisturbed movement execution, both with “reactive” balancing of external disturbances and “proactive” balancing of self-produced disturbances from the voluntary movements. Our proposals therefore target both types of disturbances and their superposition. (3) Relevant for both versatility and robustness of the control, linkages between the posture control mechanisms across DoFs provide their functional cooperation and coordination at will and on functional demands. The suggested tests therefore include ankle-hip coordination. Suggested benchmarking criteria build on the evoked sway magnitude, normalized to robot weight and Center of mass (COM) height, in relation to reference ranges that remain to be established. The references may include human likeness features. The proposed benchmarking concept may in principle also be applied to wearable robots, where a human user may command movements, but may not be aware of the additionally required postural control, which then needs to be implemented into the robot.

Postural Control of Voluntary and Involuntary Sway Movements in Healthy Young Adults

Postural Control of Voluntary and Involuntary Sway Movements in Healthy Young Adults

Using proprioception to control ongoing actions: dominance of vision or altered proprioceptive weighing?

Visual feedback is crucial for movement accuracy (e.g., Keele and Posner, J Exp Psychol 77:155-158, 1968). As well, proprioception has been argued to be important for the control of voluntary movements (e.g., Bagesteiro et al., Exp Brain Res 171:358-370, 2006; Rossetti et al., J Neurophysiol 74:457-463, 1995). While tendon vibration (TVib) has been used to perturb proprioceptive information during limb matching tasks (Goodwin et al., Science 175:1382-1384, 1972), the current study employed between-trial dual-muscle TVib, coupled with vision occlusion, to assess the use of vision and proprioception for the online control of voluntary movements. Participants (n = 17) performed an upper-limb reaching task (30cm). TVib influenced both accuracy and precision of movement endpoint. Critically, variability analyses showed that participant's performance was most affected by TVib at 75% of the movement duration, even in the presence of vision. These findings demonstrate that between-trial dual-muscle tendon vibration can perturb proprioceptive feedback, and further, suggest that proprioception can be important for the online control of reaches, even when vision is available.

Abnormal somatosensory temporal discrimination in Parkinson’s disease: Pathophysiological correlates and role in motor control deficits

ObjectiveThe somatosensory temporal discrimination threshold (STDT), defined as the shortest time interval required for two tactile stimuli to be perceived as separate, is longer in patients with Parkinson’s disease (PD). In this review, we discuss STDT findings in healthy subjects and in PD patients and the relationship between altered STDT and motor disturbances. MethodsA search was conducted on PubMed for papers dealing with PD and temporal discrimination published from January 1990 to July 2017. ResultsAbnormal STDT in PD correlates with disease duration, disease severity and degree of nigrostriatal dopamine loss, and responds to dopaminergic medication. In PD, a prolonged STDT does not correlate, or only marginally correlates, with clinically assessed bradykinesia of finger tapping. By contrast, a prolonged STDT correlates with the variability in amplitude and speed of finger tapping as assessed by means of neurophysiological techniques and may contribute to impaired finger dexterity in PD. ConclusionsWe suggest that abnormal temporal processing of sensory information in PD generates incorrect signals for the execution and control of voluntary movements. SignificanceThis review sheds light on unsolved questions regarding the relationship between STDT alterations and motor disturbances in PD and proposes directions for future research on this topic.