Proprio-tactile integration for kinesthetic perception: an fMRI study

Subcortical contributions to the sense of body ownership

The sense of body ownership (i.e. the feeling that our body or its parts belong to us) plays a key role in bodily self-consciousness and is believed to stem from multisensory integration. Experimental paradigms such as the rubber hand illusion have been developed to allow the controlled manipulation of body ownership in laboratory settings, providing effective tools for investigating malleability in the sense of body ownership and the boundaries that distinguish self from other. Neuroimaging studies of body ownership converge on the involvement of several cortical regions, including the premotor cortex and posterior parietal cortex. However, relatively less attention has been paid to subcortical structures that may also contribute to body ownership perception, such as the cerebellum and putamen. Here, on the basis of neuroimaging and neuropsychological observations, we provide an overview of relevant subcortical regions and consider their potential role in generating and maintaining a sense of ownership over the body. We also suggest novel avenues for future research targeting the role of subcortical regions in making sense of the body as our own.

Relationship between resting-state functional connectivity and change in motor function after motor imagery intervention in patients with stroke: a scoping review

BACKGROUND

In clinical practice, motor imagery has been proposed as a treatment modality for stroke owing to its feasibility in patients with severe motor impairment. Motor imagery-based interventions can be categorized as open- or closed-loop. Closed-loop intervention is based on voluntary motor imagery and induced peripheral sensory afferent (e.g., Brain Computer Interface (BCI)-based interventions). Meanwhile, open-loop interventions include methods without voluntary motor imagery or sensory afferent. Resting-state functional connectivity (rs-FC) is defined as a significant temporal correlated signal among functionally related brain regions without any stimulus. rs-FC is a powerful tool for exploring the baseline characteristics of brain connectivity. Previous studies reported changes in rs-FC after motor imagery interventions. Systematic reviews also reported the effects of motor imagery-based interventions at the behavioral level. This study aimed to review and describe the relationship between the improvement in motor function and changes in rs-FC after motor imagery in patients with stroke.

REVIEW PROCESS

The literature review was based on Arksey and O'Malley's framework. PubMed, Ovid MEDLINE, Cochrane Central Register of Controlled Trials, and Web of Science were searched up to September 30, 2023. The included studies covered the following topics: illusion without voluntary action, motor imagery, action imitation, and BCI-based interventions. The correlation between rs-FC and motor function before and after the intervention was analyzed. After screening by two independent researchers, 13 studies on BCI-based intervention, motor imagery intervention, and kinesthetic illusion induced by visual stimulation therapy were included.

CONCLUSION

All studies relating to motor imagery in this review reported improvement in motor function post-intervention. Furthermore, all those studies demonstrated a significant relationship between the change in motor function and rs-FC (e.g., sensorimotor network and parietal cortex).

Beyond sense-specific processing: decoding texture in the brain from touch and sonified movement

Texture, a fundamental object attribute, is perceived through multisensory information including touch and auditory cues. Coherent perceptions may rely on shared texture representations across different senses in the brain. To test this hypothesis, we delivered haptic textures coupled with a sound synthesizer to generate real-time textural sounds. Participants completed roughness estimation tasks with haptic, auditory, or bimodal cues in an MRI scanner. Somatosensory, auditory, and visual cortices were all activated during haptic and auditory exploration, challenging the traditional view that primary sensory cortices are sense-specific. Furthermore, audio-tactile integration was found in secondary somatosensory (S2) and primary auditory cortices. Multivariate analyses revealed shared spatial activity patterns in primary motor and somatosensory cortices, for discriminating texture across both modalities. This study indicates that primary areas and S2 have a versatile representation of multisensory textures, which has significant implications for how the brain processes multisensory cues to interact more efficiently with our environment.

Pneumatic tactile stimulus delivery system for studying brain responses evoked by active finger touch with fMRI

BACKGROUND

Primates use their hands to actively touch objects and collect information. To study tactile information processing, it is important for participants to experience tactile stimuli through active touch while monitoring brain activities.

NEW METHOD

Here, we developed a pneumatic tactile stimulus delivery system (pTDS) that delivers various tactile stimuli on a programmed schedule and allows voluntary finger touches during MRI scanning. The pTDS uses a pneumatic actuator to move tactile stimuli and place them in a finger hole. A photosensor detects the time when an index finger touches a tactile stimulus, enabling the analysis of the touch-elicited brain responses.

RESULTS

We examined brain responses while the participants actively touched braille objects presented by the pTDS. BOLD responses during tactile perception were significantly stronger in a finger touch area of the contralateral somatosensory cortex compared with that of visual perception.

CONCLUSION

The pTDS enables MR studies of brain mechanisms for tactile processes through natural finger touch.

Proprioceptive uncertainty promotes the rubber hand illusion

Body ownership is the multisensory perception of a body as one's own. Recently, the emergence of body ownership illusions like the visuotactile rubber hand illusion has been described by Bayesian causal inference models in which the observer computes the probability that visual and tactile signals come from a common source. Given the importance of proprioception for the perception of one's body, proprioceptive information and its relative reliability should impact this inferential process. We used a detection task based on the rubber hand illusion where participants had to report whether the rubber hand felt like their own or not. We manipulated the degree of asynchrony of visual and tactile stimuli delivered to the rubber hand and the real hand under two levels of proprioceptive noise using tendon vibration applied to the lower arm's antagonist extensor and flexor muscles. As hypothesized, the probability of the emergence of the rubber hand illusion increased with proprioceptive noise. Moreover, this result, well fitted by a Bayesian causal inference model, was best described by a change in the a priori probability of a common cause for vision and touch. These results offer new insights into how proprioceptive uncertainty shapes the multisensory perception of one's own body.

When proprioceptive feedback enhances visual perception of self-body movement: rehabilitation perspectives

Introduction

Rehabilitation approaches take advantage of vision's important role in kinesthesia, using the mirror paradigm as a means to reduce phantom limb pain or to promote recovery from hemiparesis. Notably, it is currently applied to provide a visual reafferentation of the missing limb to relieve amputees' pain. However, the efficiency of this method is still debated, possibly due to the absence of concomitant coherent proprioceptive feedback. We know that combining congruent visuo-proprioceptive signals at the hand level enhances movement perception in healthy people. However, much less is known about lower limbs, for which actions are far less visually controlled in everyday life than upper limbs. Therefore, the present study aimed to explore, with the mirror paradigm, the benefit of combined visuo-proprioceptive feedback from the lower limbs of healthy participants.

Methods

We compared the movement illusions driven by visual or proprioceptive afferents and tested the extent to which adding proprioceptive input to the visual reflection of the leg improved the resulting movement illusion. To this end, 23 healthy adults were exposed to mirror or proprioceptive stimulation and concomitant visuo-proprioceptive stimulation. In the visual conditions, participants were asked to voluntarily move their left leg in extension and look at its reflection in the mirror. In the proprioceptive conditions, a mechanical vibration was applied to the hamstring muscle of the leg hidden behind the mirror to simulate an extension of the leg, either exclusively or concomitantly, to the visual reflection of the leg in the mirror.

Results

(i) Visual stimulation evoked leg movement illusions but with a lower velocity than the actual movement reflection on the mirror; (ii) proprioceptive stimulation alone provided more salient illusions than the mirror illusion; and (iii) adding a congruent proprioceptive stimulation improved the saliency, amplitude, and velocity of the illusion.

Conclusion

The present findings confirm that visuo-proprioceptive integration occurs efficiently when the mirror paradigm is coupled with mechanical vibration at the lower limbs, thus providing promising new perspectives for rehabilitation.

Differentiation of claustrum resting-state functional connectivity in healthy aging, Alzheimer's disease, and Parkinson's disease

The claustrum is a sheet-like of telencephalic gray matter structure whose function is poorly understood. The claustrum is considered a multimodal computing network due to its reciprocal connections with almost all cortical areas as well as subcortical structures. Although the claustrum has been involved in several neurodegenerative diseases, specific changes in connections of the claustrum remain unclear in Alzheimer's disease (AD), and Parkinson's disease (PD). Resting-state fMRI and T1-weighted structural 3D images from healthy elderly (n = 15), AD (n = 16), and PD (n = 12) subjects were analyzed. Seed-based FC analysis was performed using CONN FC toolbox and T1-weighted images were analyzed with the Computational Anatomy Toolbox for voxel-based morphometry analysis. While we observed a decreased FC between the left claustrum and sensorimotor cortex, auditory association cortex, and cortical regions associated with social cognition in PD compared with the healthy control group (HC), no significant difference was found in alterations in the FC of both claustrum comparing the HC and AD groups. In the AD group, high FC of claustrum with regions of sensorimotor cortex and cortical regions related to cognitive control, including cingulate gyrus, supramarginal gyrus, and insular cortex were demonstrated. In addition, the structural results show significantly decreased volume in bilateral claustrum in AD and PD compared with HC. There were no significant differences in the claustrum volumes between PD and AD groups so the FC may offer more precise findings in distinguishing changes for claustrum in AD and PD.

Tinnitus Perception in Light of a Parietal Operculo-Insular Involvement: A Review

In tinnitus literature, researchers have increasingly been advocating for a clearer distinction between tinnitus perception and tinnitus-related distress. In non-bothersome tinnitus, the perception itself can be more specifically investigated: this has provided a body of evidence, based on resting-state and activation fMRI protocols, highlighting the involvement of regions outside the conventional auditory areas, such as the right parietal operculum. Here, we aim to conduct a review of available investigations of the human parietal operculo-insular subregions conducted at the microscopic, mesoscopic, and macroscopic scales arguing in favor of an auditory-somatosensory cross-talk. Both the previous literature and new results on functional connectivity derived from cortico-cortical evoked potentials show that these subregions present a dense tissue of interconnections and a strong connectivity with auditory and somatosensory areas in the healthy brain. Disrupted integration processes between these modalities may thus result in erroneous perceptions, such as tinnitus. More precisely, we highlight the role of a subregion of the right parietal operculum, known as OP3 according to the Jülich atlas, in the integration of auditory and somatosensory representation of the orofacial muscles in the healthy population. We further discuss how a dysfunction of these muscles could induce hyperactivity in the OP3. The evidence of direct electrical stimulation of this area eliciting auditory hallucinations further suggests its involvement in tinnitus perception. Finally, a small number of neuroimaging studies of therapeutic interventions for tinnitus provide additional evidence of right parietal operculum involvement.

Activity-dependent spinal cord neuromodulation rapidly restores trunk and leg motor functions after complete paralysis

Epidural electrical stimulation (EES) targeting the dorsal roots of lumbosacral segments restores walking in people with spinal cord injury (SCI). However, EES is delivered with multielectrode paddle leads that were originally designed to target the dorsal column of the spinal cord. Here, we hypothesized that an arrangement of electrodes targeting the ensemble of dorsal roots involved in leg and trunk movements would result in superior efficacy, restoring more diverse motor activities after the most severe SCI. To test this hypothesis, we established a computational framework that informed the optimal arrangement of electrodes on a new paddle lead and guided its neurosurgical positioning. We also developed software supporting the rapid configuration of activity-specific stimulation programs that reproduced the natural activation of motor neurons underlying each activity. We tested these neurotechnologies in three individuals with complete sensorimotor paralysis as part of an ongoing clinical trial ( www.clinicaltrials.gov identifier NCT02936453). Within a single day, activity-specific stimulation programs enabled these three individuals to stand, walk, cycle, swim and control trunk movements. Neurorehabilitation mediated sufficient improvement to restore these activities in community settings, opening a realistic path to support everyday mobility with EES in people with SCI.

Bimanual coupling effect during a proprioceptive stimulation

Circle-line drawing paradigm is used to study bimanual coupling. In the standard paradigm, subjects are asked to draw circles with one hand and lines with the other hand; the influence of the concomitant tasks results in two "elliptical" figures. Here we tested whether proprioceptive information evoked by muscle vibration inducing a proprioceptive illusion (PI) of movement at central level, was able to affect the contralateral hand drawing circles or lines. A multisite 80 Hz-muscle vibration paradigm was used to induce the illusion of circle- and line-drawing on the right hand of 15 healthy participants. During muscle vibration, subjects had to draw a congruent or an incongruent figure with the left hand. The ovalization induced by PI was compared with Real and Motor Imagery conditions, which already have proved to induce bimanual coupling. We showed that the ovalization of a perceived circle over a line drawing during PI was comparable to that observed in Real and Motor Imagery condition. This finding indicates that PI can induce bimanual coupling, and proprioceptive information can influence the motor programs of the contralateral hand.

Cutaneous and muscular afferents from the foot and sensory fusion processing: Physiology and pathology in neuropathies

The foot-sole cutaneous receptors (section 2), their function in stance control (sway minimisation, exploratory role) (2.1), and the modulation of their effects by gait pattern and intended behaviour (2.2) are reviewed. Experimental manipulations (anaesthesia, temperature) (2.3 and 2.4) have shown that information from foot sole has widespread influence on balance. Foot-sole stimulation (2.5) appears to be a promising approach for rehabilitation. Proprioceptive information (3) has a pre-eminent role in balance and gait. Reflex responses to balance perturbations are produced by both leg and foot muscle stretch (3.1) and show complex interactions with skin input at both spinal and supra-spinal levels (3.2), where sensory feedback is modulated by posture, locomotion and vision. Other muscles, notably of neck and trunk, contribute to kinaesthesia and sense of orientation in space (3.3). The effects of age-related decline of afferent input are variable under different foot-contact and visual conditions (3.4). Muscle force diminishes with age and sarcopenia, affecting intrinsic foot muscles relaying relevant feedback (3.5). In neuropathy (4), reduction in cutaneous sensation accompanies the diminished density of viable receptors (4.1). Loss of foot-sole input goes along with large-fibre dysfunction in intrinsic foot muscles. Diabetic patients have an elevated risk of falling, and vision and vestibular compensation strategies may be inadequate (4.2). From Charcot-Marie-Tooth 1A disease (4.3) we have become aware of the role of spindle group II fibres and of the anatomical feet conditions in balance control. Lastly (5) we touch on the effects of nerve stimulation onto cortical and spinal excitability, which may participate in plasticity processes, and on exercise interventions to reduce the impact of neuropathy.

Differences in Proprioception Between Young and Middle-Aged Adults With and Without Chronic Low Back Pain

Introduction: While young adults with chronic low back pain (CLBP) exhibit impaired lumbar proprioception, it remains unclear if the same phenomenon is observed in middle-aged adults with CLBP. Objectives: This study aimed to investigate whether young or middle-aged adults with CLBP displayed different proprioception ability as compared to age-matched asymptomatic controls. Methods: Sixty-four young adults with [median age:34 [interquartile range (IQR): 29-37] years] and without [median age:29 (IQR; 23-34) years] CLBP, and 87 middle-aged adults with [median age:53 (IQR: 49-58) years] and without [median age: 54 (IQR: 45-64) years] CLBP underwent postural sway tests on a force-plate with (unstable surface) and without a foam (stable surface), while bilateral L5/S1 multifidi and triceps-surae were vibrated separately. An individual's proprioception reweighting ability was estimated by relative proprioceptive reweighting (RPW). Higher RPW values indicate less reliance on lumbar multifidus proprioceptive signals for balance. Participants also underwent lumbar repositioning tests in sitting to determine repositioning errors in reproducing target lumbar flexion/extension positions. Results: Young adults with CLBP demonstrated significantly higher median RPW values than age-matched asymptomatic controls for maintaining standing balance [stable surface: CLBP: 0.9 (IQR: 0.7-0.9), asymptomatic: 0.7 (IQR: 0.6-0.8), p < 0.05; unstable surface: CLBP: 0.6 (IQR: 0.4-0.8), asymptomatic: 0.5 (IQR: 0.3-0.7), p < 0.05]. No significant differences in repositioning error were noted between young or middle-aged adults with and without CLBP (p > 0.05). RPW values were unrelated to repositioning errors in all groups (p > 0.05). Conclusion: Young adults with CLBP, and middle-aged adults with and without CLBP had inferior proprioceptive reweighting capability. This finding may indicate potential age-related deterioration in central and peripheral processing of lumbar proprioceptive signals. Future studies should use advanced imaging and/or electroencephalogram to determine mechanisms underlying changes in proprioceptive reweighting in middle-aged adults.

Functional properties of extended body representations in the context of kinesthesia

A person's internal representation of his/her body is not fixed. It can be substantially modified by neurological injuries and can also be extended (in healthy participants) to incorporate objects that have a corporeal appearance (such as fake body segments, e.g. a rubber hand), virtual whole bodies (e.g. avatars), and even objects that do not have a corporeal appearance (e.g. tools). Here, we report data from patients and healthy participants that emphasize the flexible nature of body representation and question the extent to which incorporated objects have the same functional properties as biological body parts. Our data shed new light by highlighting the involvement of visual motion information from incorporated objects (rubber hands, full body avatars and hand-held tools) in the perception of one's own movement (kinesthesia). On the basis of these findings, we argue that incorporated objects can be treated as body parts, especially when kinesthesia is involved.

Effect of primary motor cortex excitability changes after quadripulse transcranial magnetic stimulation on kinesthetic sensitivity: A preliminary study

Muscle spindles provide the greatest contribution to kinesthetic perception. Primary motor cortex (M1) excitability changes in parallel with the intensity of kinesthetic perception inputs from muscle spindles; M1 is therefore involved in kinesthetic perception. However, the causal relationship between changes in kinesthetic sensitivity and M1 excitability is unclear. The purpose of this study was to test whether artificially and sustainably modulated M1 excitability causes changes in kinesthetic sensitivity in healthy individuals. We evaluated motor evoked potentials (MEP) in Experiment 1 and joint motion detection thresholds (JMDT) in Experiment 2 before and after quadripulse transcranial magnetic stimulation (QPS). Nine healthy right-handed male volunteers were recruited. In each experiment, participants received QPS or sham stimulation (Sham) on separate days. MEP amplitude and JMDT were recorded before and at 0, 15, 30, 45, and 60 min after QPS and Sham. Our results showed that M1 excitability and kinesthetic sensitivity increased after QPS, whereas neither changed after Sham. In the five subjects who participated in both experiments, there was a significant moderate correlation between M1 excitability and kinesthetic sensitivity. Thus, the long-lasting change in kinesthetic sensitivity may be due to changes in M1 excitability. In addition, M1 may play a gain adjustment role in the neural pathways of muscle spindle input.

Functional brain changes in the elderly for the perception of hand movements: A greater impairment occurs in proprioception than touch

Unlike age-related brain changes linked to motor activity, neural alterations related to self-motion perception remain unknown. Using fMRI data, we investigated age-related changes in the central processing of somatosensory information by inducing illusions of right-hand rotations with specific proprioceptive and tactile stimulation. Functional connectivity during resting-state (rs-FC) was also compared between younger and older participants. Results showed common sensorimotor activations in younger and older adults during proprioceptive and tactile illusions, but less deactivation in various right frontal regions and the precuneus were found in the elderly. Older participants exhibited a less-lateralized pattern of activity across the primary sensorimotor cortices (SM1) in the proprioceptive condition only. This alteration of the interhemispheric balance correlated with declining individual performance in illusion velocity perception from a proprioceptive, but not a tactile, origin. By combining task-related data, rs-FC and behavioral performance, this study provided consistent results showing that hand movement perception was altered in the elderly, with a more pronounced deterioration of the proprioceptive system, likely due to the breakdown of inhibitory processes with aging. Nevertheless, older people could benefit from an increase in internetwork connectivity to overcome this kinesthetic decline.

Changes in the Organization of the Secondary Somatosensory Cortex While Processing Lumbar Proprioception and the Relationship With Sensorimotor Control in Low Back Pain

OBJECTIVES

Patients with nonspecific low back pain (NSLBP) rely more on the ankle compared with the lower back proprioception while standing, perform sit-to-stand-to-sit (STSTS) movements slower, and exhibit perceptual impairments at the lower back. However, no studies investigated whether these sensorimotor impairments relate to a reorganization of the primary and secondary somatosensory cortices (S1 and S2) and primary motor cortex (M1) during proprioceptive processing.

MATERIALS AND METHODS

Proprioceptive stimuli were applied at the lower back and ankle muscles during functional magnetic resonance imaging in 15 patients with NSLBP and 13 controls. The location of the activation peaks during the processing of proprioception within S1, S2, and M1 were determined and compared between groups. Proprioceptive use during postural control was evaluated, the duration to perform 5 STSTS movements was recorded, and participants completed the Fremantle Back Awareness Questionnaire (FreBAQ) to assess back-specific body perception.

RESULTS

The activation peak during the processing of lower back proprioception in the right S2 was shifted laterally in the NSLBP group compared with the healthy group (P=0.007). Moreover, patients with NSLSP performed STSTS movements slower (P=0.018), and reported more perceptual impairments at the lower back (P<0.001). Finally, a significant correlation between a more lateral location of the activation peak during back proprioceptive processing and a more disturbed body perception was found across the total group (ρ=0.42, P=0.025).

CONCLUSIONS

The results suggest that patients with NSLBP show a reorganization of the higher-order processing of lower back proprioception, which could negatively affect spinal control and body perception.

The aging brain: A set of functional MRI data acquired at rest and during exposure to tactile or muscle proprioceptive stimulation in healthy young and older volunteers

There is a growing interest in understanding functional brain decline with aging. The dataset provides raw anatomical and functional images recorded in a group of 20 young volunteers and in another group of 19 older volunteers during a 10-minute period of resting state followed by four consecutive task-related runs. During each task-related run, the participants were exposed to two types of sensory stimulation: a tactile stimulation consisting in a textured-disk rotation under the palm of their right hand or a muscle proprioceptive stimulation consisting in a mechanical vibration applied to the muscle tendon of their wrist abductor. These two stimulations are known to evoke illusory sensations of hand movement, while the hand remains actually still. Therefore, the dataset is meant to be used to assess age-related functional brain changes during the perception of hand movements based on muscle proprioception or touch individually. It also allows to explore any structural changes or functional resting connectivity alteration with aging. The dataset is a supplement to the research findings in the paper ‘Functional brain changes in the elderly for the perception of hand movements: a greater impairment occurs in proprioception than touch published in NeuroImage.

Errors in proprioceptive matching post-stroke are associated with impaired recruitment of parietal, supplementary motor, and temporal cortices

Deficits in proprioception, the ability to discriminate the relative position and movement of our limbs, affect ~50% of stroke patients and reduce functional outcomes. Our lack of knowledge of the anatomical correlates of proprioceptive processing limits our understanding of the impact that such deficits have on recovery. This research investigated the relationship between functional impairment in brain activity and proprioception post-stroke. We developed a novel device and task for arm position matching during functional MRI (fMRI), and investigated 16 subjects with recent stroke and nine healthy age-matched controls. The stroke-affected arm was moved by an experimenter (passive arm), and subjects were required to match the position of this limb with the opposite arm (active arm). Brain activity during passive and active arm movements was determined, as well as activity in association with performance error. Passive arm movement in healthy controls was associated with activity in contralateral primary somatosensory (SI) and motor cortices (MI), bilateral parietal cortex, supplementary (SMA) and premotor cortices, secondary somatosensory cortices (SII), and putamen. Active arm matching was associated with activity in contralateral SI, MI, bilateral SMA, premotor cortex, putamen, and ipsilateral cerebellum. In subjects with stroke, similar patterns of activity were observed. However, in stroke subjects, greater proprioceptive error was associated with less activity in ipsilesional supramarginal and superior temporal gyri, and lateral thalamus. During active arm movement, greater proprioceptive error was associated with less activity in bilateral SMA and ipsilesional premotor cortex. Our results enhance our understanding of the correlates of proprioception within the temporal parietal cortex and supplementary/premotor cortices. These findings also offer potential targets for therapeutic intervention to improve proprioception in recovering stroke patients and thus improve functional outcome.

Temporal Discrimination Thresholds and Proprioceptive Performance: Impact of Age and Nerve Conduction

Background

Increasing attention is payed to the contribution of somatosensory processing in motor control. In particular, temporal somatosensory discrimination has been found to be altered differentially in common movement disorders. To date, there have only been speculations as to how impaired temporal discrimination and clinical motor signs may relate to each other. Prior to disentangling this relationship, potential confounders of temporal discrimination, in particular age and peripheral nerve conduction, should be assessed, and a quantifiable measure of proprioceptive performance should be established.

Objective

To assess the influence of age and polyneuropathy (PNP) on somatosensory temporal discrimination threshold (STDT), temporal discrimination movement threshold (TDMT), and behavioral measures of proprioception of upper and lower limbs.

Methods

STDT and TDMT were assessed in 79 subjects (54 healthy, 25 with PNP; age 30–79 years). STDT was tested with surface electrodes over the thenar or dorsal foot region. TDMT was probed with needle electrodes in flexor carpi radialis (FCR) and tibialis anterior (TA) muscle. Goniometer-based devices were used to assess limb proprioception during (i) active pointing to LED markers, (ii) active movements in response to variable visual cues, and (iii) estimation of limb position following passive movements. Pointing (or estimation) error was taken as a measure of proprioceptive performance.

Results

In healthy subjects, higher age was associated with higher STDT and TDMT at upper and lower extremities, while age did not correlate with proprioceptive performance. Patients with PNP showed higher STDT and TDMT values and decreased proprioceptive performance in active pointing tasks compared to matched healthy subjects. As an additional finding, there was a significant correlation between performance in active pointing tasks and temporal discrimination thresholds.

Conclusion

Given their notable impact on measures of temporal discrimination, age and peripheral nerve conduction need to be accounted for if STDT and TDMT are applied in patients with movement disorders. As a side observation, the correlation between measures of proprioception and temporal discrimination may prompt further studies on the presumptive link between these two domains.

Low Back Pain: The Potential Contribution of Supraspinal Motor Control and Proprioception

Motor control, which relies on constant communication between motor and sensory systems, is crucial for spine posture, stability and movement. Adaptions of motor control occur in low back pain (LBP) while different motor adaption strategies exist across individuals, probably to reduce LBP and risk of injury. However, in some individuals with LBP, adapted motor control strategies might have long-term consequences, such as increased spinal loading that has been linked with degeneration of intervertebral discs and other tissues, potentially maintaining recurrent or chronic LBP. Factors contributing to motor control adaptations in LBP have been extensively studied on the motor output side, but less attention has been paid to changes in sensory input, specifically proprioception. Furthermore, motor cortex reorganization has been linked with chronic and recurrent LBP, but underlying factors are poorly understood. Here, we review current research on behavioral and neural effects of motor control adaptions in LBP. We conclude that back pain-induced disrupted or reduced proprioceptive signaling likely plays a pivotal role in driving long-term changes in the top-down control of the motor system via motor and sensory cortical reorganization. In the outlook of this review, we explore whether motor control adaptations are also important for other (musculoskeletal) pain conditions.

Hand-eye coordination, movement reaction time and hand tactile sensitivity depending on the practiced sports discipline

BACKGROUND

Practicing competitive sports, particularly those disciplines in which the upper limbs are involved in the movement, develops physical fitness and its special feature, namely the hand-eye coordination. Some sport disciplines require manipulation of an object. Using a sport equipment every day, several times, during training and matches must affect the characteristics of the skin of the palmar side of the hand. It may be presumed to affect the tactile sensitivity of the skin. The aim of the study was to determine the relationship between hand-eye coordination and tactile sensitivity in basketball, volleyball, handball, football and combat sports players as compared to those who do not practice competitive sports.

METHODS

Overall, 121 men were subject to tests. The tactile sensitivity threshold was determined at three points of the palmar side of the hand using The Touch-Test™ Sensory Evaluators esthesiometer. The second test involved hand-eye coordination of the upper limbs and it was carried out using cross-type machine.

RESULTS

The greatest tactile sensitivity was shown in combat sports players. These players also demonstrated the shortest reaction time and the lowest number of errors in the motor coordination test. The correlation between tactile sensitivity and coordination was found to be the strongest in subjects not practicing sports.

CONCLUSIONS

The most interesting finding is that in the group of athletes using hands (team sports games and combat sports) the correlation between movement coordination and tactile sensitivity is weaker.

Event-related desynchronization possibly discriminates the kinesthetic illusion induced by visual stimulation from movement observation

Visual stimulation of a repetitive self-movement image can evoke kinesthetic illusion when a virtual body part is set over the actual body part (kinesthetic illusion induced by visual stimulation, KINVIS). KINVIS induces activity in cerebral network, similar to that produced during motor execution, and triggers motor imagery passively. This study sought to identify a biomarker of KINVIS using event-related desynchronization (ERD) to improve the application of KINVIS to brain-machine interface (BMI) therapy of patients with stroke with hemiparesis. We included healthy adults in whom KINVIS could be induced. Scalp electroencephalograms were recorded during the KINVIS condition, where KINVIS was induced using a self-movement image. The findings were compared to signals recorded during an observation (OB) condition where only the self-movement image was viewed. For the signal intensity of the α- and low β-frequency bands, we calculated ERD during a movie period. The ERD of the α-frequency band in P3 and CP3 during KINVIS was significantly higher than that during OB. Furthermore, using the ERD of the α-frequency band recorded from FC3 and CP3, we could discriminate illusory perception with a 70% success rate. In this study, KINVIS could be detected using the ERD of the α-frequency band recorded from the posterior portion of the sensorimotor cortex. Furthermore, adding ERD recorded from FC3 to that recorded from CP3 may enable the objective discrimination of KINVIS from OB. When applying KINVIS in BMI therapy, the combination ERD of FC3 and CP3 will become a parameter for objectively judging the degree of kinesthetic perception achieved.

Target-oriented motor imagery for grasping action: different characteristics of brain activation between kinesthetic and visual imagery

Motor imagery (MI) for target-oriented movements, which is a basis for functional activities of daily living, can be more appropriate than non-target-oriented MI as tasks to promote motor recovery or brain-computer interface (BCI) applications. This study aimed to explore different characteristics of brain activation among target-oriented kinesthetic imagery (KI) and visual imagery (VI) in the first-person (VI-1) and third-person (VI-3) perspectives. Eighteen healthy volunteers were evaluated for MI ability, trained for the three types of target-oriented MIs, and scanned using 3 T functional magnetic resonance imaging (fMRI) under MI and perceptual control conditions, presented in a block design. Post-experimental questionnaires were administered after fMRI. Common brain regions activated during the three types of MI were the left premotor area and inferior parietal lobule, irrespective of the MI modalities or perspectives. Contrast analyses showed significantly increased brain activation only in the contrast of KI versus VI-1 and KI versus VI-3 for considerably extensive brain regions, including the supplementary motor area and insula. Neural activity in the orbitofrontal cortex and cerebellum during VI-1 and KI was significantly correlated with MI ability measured by mental chronometry and a self-reported questionnaire, respectively. These results can provide a basis in developing MI-based protocols for neurorehabilitation to improve motor recovery and BCI training in severely paralyzed individuals.

A two alternative forced choice method for assessing vibrotactile discrimination thresholds in the lower limb

The development of an easy to implement, quantitative measure to examine vibration perception would be useful for future application in clinical settings. Vibration sense in the lower limb of younger and older adults was examined using the method of constant stimuli (MCS) and the two-alternative forced choice paradigm. The focus of this experiment was to determine an appropriate stimulation site on the lower limb (tendon versus bone) to assess vibration threshold and to determine if the left and right legs have varying thresholds. Discrimination thresholds obtained at two stimulation sites in the left and right lower limbs showed differences in vibration threshold across the two ages groups, but not across sides of the body nor between stimulation sites within each limb. Overall, the MCS can be implemented simply, reliably, and with minimal time. It can also easily be implemented with low-cost technology. Therefore, it could be a good candidate method to assess the presence of specific deep sensitivity deficits in clinical practice, particularly in populations likely to show the onset of sensory deficits.

Important Movement Concepts: Clinical Versus Neuroscience Perspectives

Human movement is complex, presenting clinical and research challenges regarding how it is described and investigated. This paper discusses the commonalities and differences on how human movement is conceptualized from neuroscientific and clinical perspectives with respect to postural control; the limitations of linear measures; movement efficiency with respect to metabolic energy cost and selectivity; and, how muscle synergy analysis may contribute to our understanding of movement variability. We highlight the role of sensory information on motor performance with respect to the base of support and alignment, illustrating a potential disconnect between the clinical and neuroscientific perspectives. The purpose of this paper is to discuss the commonalities and differences in how movement concepts are defined and operationalized by Bobath clinicians and the neuroscientific community to facilitate a common understanding and open the dialogue on the research practice gap.

Differences in brain processing of proprioception related to postural control in patients with recurrent non-specific low back pain and healthy controls

Patients with non-specific low back pain (NSLBP) show an impaired postural control during standing and a slower performance of sit-to-stand-to-sit (STSTS) movements. Research suggests that these impairments could be due to an altered use of ankle compared to back proprioception. However, the neural correlates of these postural control impairments in NSLBP remain unclear. Therefore, we investigated brain activity during ankle and back proprioceptive processing by applying local muscle vibration during functional magnetic resonance imaging in 20 patients with NSLBP and 20 controls. Correlations between brain activity during proprioceptive processing and (Airaksinen et al., 2006) proprioceptive use during postural control, evaluated by using muscle vibration tasks during standing, and (Altmann et al., 2007) STSTS performance were examined across and between groups. Moreover, fear of movement was assessed. Results revealed that the NSLBP group performed worse on the STSTS task, and reported more fear compared to healthy controls. Unexpectedly, no group differences in proprioceptive use during postural control were found. However, the relationship between brain activity during proprioceptive processing and behavioral indices of proprioceptive use differed significantly between NSLBP and healthy control groups. Activity in the right amygdala during ankle proprioceptive processing correlated with an impaired proprioceptive use in the patients with NSLBP, but not in healthy controls. Moreover, while activity in the left superior parietal lobule, a sensory processing region, during back proprioceptive processing correlated with a better use of proprioception in the NSLBP group, it was associated with a less optimal use of proprioception in the control group. These findings suggest that functional brain changes during proprioceptive processing in patients with NSLBP may contribute to their postural control impairments.

Seeing Your Foot Move Changes Muscle Proprioceptive Feedback

Multisensory effects are found when the input from single senses combines, and this has been well researched in the brain. Presently, we examined in humans the potential impact of visuo-proprioceptive interactions at the peripheral level, using microneurography, and compared it with a similar behavioral task. We used a paradigm where participants had either proprioceptive information only (no vision) or combined visual and proprioceptive signals (vision). We moved the foot to measure changes in the sensitivity of single muscle afferents, which can be altered by the descending fusimotor drive. Visual information interacted with proprioceptive information, where we found that for the same passive movement, the response of muscle afferents increased when the proprioceptive channel was the only source of information, as compared with when visual cues were added, regardless of the attentional level. Behaviorally, when participants looked at their foot moving, they more accurately judged differences between movement amplitudes, than in the absence of visual cues. These results impact our understanding of multisensory interactions throughout the nervous system, where the information from different senses can modify the sensitivity of peripheral receptors. This has clinical implications, where future strategies may modulate such visual signals during sensorimotor rehabilitation.

Association Between Sensorimotor Impairments and Functional Brain Changes in Patients With Low Back Pain: A Critical Review

Low back pain (LBP) coincides with sensorimotor impairments, for example, reduced lumbosacral tactile and proprioceptive acuity and postural control deficits. Recent functional magnetic resonance imaging studies suggest that sensorimotor impairments in LBP may be associated with brain changes. However, no consensus exists regarding the relationship between functional brain changes and sensorimotor behavior in LBP. Therefore, this review critically discusses the available functional magnetic resonance imaging studies on brain activation related to nonnociceptive somatosensory stimulation and motor performance in individuals with LBP. Four electronic databases were searched, yielding nine relevant studies. Patients with LBP showed reduced sensorimotor-related brain activation and a reorganized lumbar spine representation in higher-order (multi)sensory processing and motor regions, including primary and secondary somatosensory cortices, supplementary motor area, and superior temporal gyrus. These results may support behavioral findings of sensorimotor impairments in LBP. In addition, patients with LBP displayed widespread increased sensorimotor-evoked brain activation in regions often associated with abnormal pain processing. Overactivation in these regions could indicate an overresponsiveness to sensory inputs that signal potential harm to the spine, thereby inducing overgeneralized protective responses. Hence, functional brain changes could contribute to the development and recurrence of LBP. However, future studies investigating the causality between sensorimotor-related brain function and LBP are imperative.

Linear Integration of Tactile and Non-tactile Inputs Mediates Estimation of Fingertip Relative Position

While skin, joints and muscles receptors alone provide lower level information about individual variables (e.g., exerted limb force and limb displacement), the distance between limb endpoints (i.e., relative position) has to be extracted from high level integration of somatosensory and motor signals. In particular, estimation of fingertip relative position likely involves more complex sensorimotor transformations than those underlying hand or arm position sense: the brain has to estimate where each fingertip is relative to the hand and where fingertips are relative to each other. It has been demonstrated that during grasping, feedback of digit position drives rapid adjustments of fingers force control. However, it has been shown that estimation of fingertips' relative position can be biased by digit forces. These findings raise the question of how the brain combines concurrent tactile (i.e., cutaneous mechanoreceptors afferents induced by skin pressure and stretch) and non-tactile (i.e., both descending motor command and joint/muscle receptors signals associated to muscle contraction) digit force-related inputs for fingertip distance estimation. Here we addressed this question by quantifying the contribution of tactile and non-tactile force-related inputs for the estimation of fingertip relative position. We asked subjects to match fingertip vertical distance relying only on either tactile or non-tactile inputs from the thumb and index fingertip, and compared their performance with the condition where both types of inputs were combined. We found that (a) the bias in the estimation of fingertip distance persisted when tactile inputs and non-tactile force-related signals were presented in isolation; (b) tactile signals contributed the most to the estimation of fingertip distance; (c) linear summation of the matching errors relying only on either tactile or non-tactile inputs was comparable to the matching error when both inputs were simultaneously available. These findings reveal a greater role of tactile signals for sensing fingertip distance and suggest a linear integration mechanism with non-tactile inputs for the estimation of fingertip relative position.

Postoperative Treatment of Distal Radius Fractures Using Sensorimotor Rehabilitation

Background  Sensorimotor and specifically proprioception sense has been used in rehabilitation to treat neurological and joint injuries. These feedback loops are not well understood or implemented in wrist treatment. We observed a temporary sensorimotor loss, following distal radius fractures (DRF) that should be addressed postsurgery. Purpose  The purpose of this prospective therapeutic study was to compare the outcomes of patients following surgery for DRF treated using a sensorimotor treatment protocol with those patients treated according to the postoperative standard of care. Patients and Methods  Patients following surgery for DRF sent for hand therapy were eligible for the study. Both the evaluation and treatment protocols included a comprehensive sensorimotor panel. Patients were randomized into standard and standard plus sensorimotor postoperative therapy and were evaluated a few days following surgery, at 6 weeks, and 3 months postsurgery. Results  Sixty patients following surgery were randomized into the two treatment regimens. The initial evaluation was similar for both groups and both demonstrated significant sensorimotor deficits, following surgery for DRF. There was documented sensorimotor and functional improvement in both groups with treatment. The clinical results were better in the group treated with the sensorimotor-proprioception protocol mostly in the wrist; however, not all of the differences were significant. Conclusion  Patients after surgery for DRF demonstrate significant sensorimotor deficits which may improve faster when utilizing a comprehensive sensorimotor treatment protocol. However, we did not demonstrate efficacy of the protocol in treating proprioceptive deficits. Further study should include refinement of functional outcome evaluation, studying of the treatment protocol, and establishment of sensorimotor therapeutic guidelines for other conditions. Level of Evidence This is a level II, therapeutic study.

Activation of Bilateral Secondary Somatosensory Cortex With Right Hand Touch Stimulation: A Meta-Analysis of Functional Neuroimaging Studies

Background: Brain regions involved in processing somatosensory information have been well documented through lesion, post-mortem, animal, and more recently, structural and functional neuroimaging studies. Functional neuroimaging studies characterize brain activation related to somatosensory processing; yet a meta-analysis synthesis of these findings is currently lacking and in-depth knowledge of the regions involved in somatosensory-related tasks may also be confounded by motor influences. Objectives: Our Activation Likelihood Estimate (ALE) meta-analysis sought to quantify brain regions that are involved in the tactile processing of the right (RH) and left hands (LH) separately, with the exclusion of motor related activity. Methods: The majority of studies (n = 41) measured activation associated with RH tactile stimulation. RH activation studies were grouped into those which conducted whole-brain analyses (n = 29) and those which examined specific regions of interest (ROI; n = 12). Few studies examined LH activation, though all were whole-brain studies (N = 7). Results: Meta-analysis of brain activation associated with RH tactile stimulation (whole-brain studies) revealed large clusters of activation in the left primary somatosensory cortex (S1) and bilaterally in the secondary somatosensory cortex (S2; including parietal operculum) and supramarginal gyrus (SMG), as well as the left anterior cingulate. Comparison between findings from RH whole-brain and ROI studies revealed activation as expected, but restricted primarily to S1 and S2 regions. Further, preliminary analyses of LH stimulation studies only, revealed two small clusters within the right S1 and S2 regions, likely limited due to the small number of studies. Contrast analyses revealed the one area of overlap for RH and LH, was right secondary somatosensory region. Conclusions: Findings from the whole-brain meta-analysis of right hand tactile stimulation emphasize the importance of taking into consideration bilateral activation, particularly in secondary somatosensory cortex. Further, the right parietal operculum/S2 region was commonly activated for right and left hand tactile stimulation, suggesting a lateralized pattern of somatosensory activation in right secondary somatosensory region. Implications for further research and for possible differences in right and left hemispheric stroke lesions are discussed.

Role-Specific Brain Activations in Leaders and Followers During Joint Action

Much of social interaction in human life requires that individuals perform different roles during joint actions, the most basic distinction being that between a leader and a follower. A number of neuroimaging studies have examined the brain networks for leading and following, but none have examined what effect prior expertise at these roles has on brain activations during joint motor tasks. Couple dancers (e.g., dancers of Tango, Salsa, and swing) are an ideal population in which examine such effects, since leaders and followers of partnered dances have similar overall levels of motor expertise at dancing, but can differ strikingly in their role-specific skill sets. To explore role-specific expertise effects on brain activations for the first time, we recruited nine skilled leaders and nine skilled followers of couple dances for a functional magnetic resonance imaging study. We employed a two-person scanning arrangement that allowed a more naturalistic interaction between two individuals. The dancers interacted physically with an experimenter standing next to the bore of the magnet so as to permit bimanual partnered movements. Together, they alternated between leading and following the joint movements. The results demonstrated that the brain activations during the acts of leading and following were enhanced by prior expertise at being a leader or follower, and that activity in task-specific brain areas tended to be positively correlated with the level of expertise at the corresponding role. These findings provide preliminary evidence that training at one role of a joint motor task can selectively enhance role-related brain activations.

Evaluating the effects of delivering integrated kinesthetic and tactile cues to individuals with unilateral hemiparetic stroke during overground walking

BACKGROUND

Integration of kinesthetic and tactile cues for application to post-stroke gait rehabilitation is a novel concept which needs to be explored. The combined provision of haptic cues may result in collective improvement of gait parameters such as symmetry, balance and muscle activation patterns. Our proposed integrated cue system can offer a cost-effective and voluntary gait training experience for rehabilitation of subjects with unilateral hemiparetic stroke.

METHODS

Ten post-stroke ambulatory subjects participated in a 10 m walking trial while utilizing the haptic cues (either alone or integrated application), at their preferred and increased gait speeds. In the system a haptic cane device (HCD) provided kinesthetic perception and a vibrotactile feedback device (VFD) provided tactile cue on the paretic leg for gait modification. Balance, gait symmetry and muscle activity were analyzed to identify the benefits of utilizing the proposed system.

RESULTS

When using kinesthetic cues, either alone or integrated with a tactile cue, an increase in the percentage of non-paretic peak activity in the paretic muscles was observed at the preferred gait speed (vastus medialis obliquus: p <  0.001, partial eta squared (η2) = 0.954; semitendinosus p <  0.001, partial η2 = 0.793) and increased gait speeds (vastus medialis obliquus: p <  0.001, partial η2 = 0.881; semitendinosus p = 0.028, partial η2 = 0.399). While using HCD and VFD (individual and integrated applications), subjects could walk at their preferred and increased gait speeds without disrupting trunk balance in the mediolateral direction. The temporal stance symmetry ratio was improved when using tactile cues, either alone or integrated with a kinesthetic cue, at their preferred gait speed (p <  0.001, partial η2 = 0.702).

CONCLUSIONS

When combining haptic cues, the subjects walked at their preferred gait speed with increased temporal stance symmetry and paretic muscle activity affecting their balance. Similar improvements were observed at higher gait speeds. The efficacy of the proposed system is influenced by gait speed. Improvements were observed at a 20% increased gait speed, whereas, a plateau effect was observed at a 40% increased gait speed. These results imply that integration of haptic cues may benefit post-stroke gait rehabilitation by inducing simultaneous improvements in gait symmetry and muscle activity.

When the vibrations allow for anticipating the force to be produced: an extend to Pfister et al. (2014)

According to the ideomotor theory, action selection is done by the mental anticipation of its perceptual consequences. If the distal information processed mainly by vision and hearing are considered essential for the representation of the action, the proximal information processed by the sense of touch and proprioception is of less importance. Recent works seem to show the opposite. Nevertheless, it is necessary to complete these results by offering a situation, more ecological, where response and effect can occur on the same effector. So, the goal of our work was to implement a more relevant spatial correspondence because to touch is not the same action that to hear or to see. To do so, participants pressed a specific key after the presentation of a stimulus. The key vibrated depending on the pressure exerted on it. In a compatible condition, high pressure on a key triggered a high vibration, while in an incompatible condition high pressure triggered a low vibration on the same effectors. As expected, the response times were faster in the compatible condition than the incompatible condition. This means that proximal information participates actively in the selection of action.

Peripheral and central determinants of skin wetness sensing in humans

Evolutionarily, our ability to sense skin wetness and humidity (i.e., hygroreception) could have developed as a way of helping to maintain thermal homeostasis, as much as it is the case for the role of temperature sensation and thermoreception. Humans are not provided with a specific skin hygroreceptor, and recent studies have indicated that skin wetness is likely to be centrally processed as a result of the multisensory integration of peripheral inputs from skin thermoreceptors and mechanoreceptors coding the biophysical interactions between skin and moisture. The existence of a specific hygrosensation strategy for human wetness perception has been proposed and the first neurophysiologic model of skin wetness sensing has been recently developed. However, while these recent findings have shed light on some of the peripheral and central neural mechanisms underlying wetness sensing, our understanding of how the brain processes the thermal and mechanical inputs that give rise to one of our "most worn" skin sensory experiences is still far from being conclusive. Understanding these neural mechanisms is clinically relevant in the context of those neurologic conditions that are accompanied by somatosensory abnormalities. The present chapter will present the current knowledge on the peripheral and central determinants of skin wetness sensing in humans.

Visuomotor effects of body part movements presented in the first-person perspective on imitative behavior

Imitative stimuli presented from a first-person perspective (FPP) produce stronger visuomotor effects than those presented from a third-person perspective (TPP) due to the relatively greater response of the mirror neuron system (MNS) to FPP stimuli. Some previous studies utilizing TPP stimuli have reported no differences in MNS activity between moving and static bodies' stimuli. However, few studies have compared visuomotor effects of such stimuli when presented in the FPP. To clarify this issue, we measured cortical activation in 17 participants during a functional magnetic resonance imaging (MRI) imitation task involving three conditions: moving (a lifting finger was presented), static (an "X" appeared on a static finger), and control (an "X" appeared on a button). All stimuli were presented from the FPP or TPP. Participants were asked to lift the finger corresponding to the imitative stimulus. In the FPP condition, moving stimuli elicited greater MNS activation than static stimuli. Furthermore, such movement effects were stronger in the MNS and insula (a region associated with body-ownership) for FPP stimuli than for TPP stimuli. Psychophysiological interaction analysis revealed increased connectivity between the MNS and insula for moving stimuli in the FPP condition. These findings suggest that bodily movements presented in the FPP elicit a greater visuomotor response than static body presented in the FPP, and that the visuomotor effects of bodily movements were greater in the FPP condition than in the TPP condition. Our analyses further indicated that such responses are processed via the neural system underlying body-ownership. Hum Brain Mapp 38:6218-6229, 2017. © 2017 Wiley Periodicals, Inc.

Contrasting effects of adaptation to a visuomotor rotation on explicit and implicit measures of sensory coupling

We previously investigated sensory coupling of the sensed positions of cursor and hand in a cursor-control task and found differential characteristics of implicit and explicit measures of the bias of sensed hand position toward the position of the cursor. The present study further tested whether adaptation to a visuomotor rotation differentially affects these two measures. Participants made center-out reaching movements to remembered targets while looking at a rotated feedback cursor. After sets of practice trials with constant (adaptation condition) or random (control condition) visuomotor rotations, test trials served to assess sensory coupling. In these trials, participants judged the position of the hand at the end of the center-out movement, and the deviation of these judgments from the physical hand positions served as explicit measure of the bias of sensed hand position toward the position of the cursor, whereas the implicit measure was based on the direction of the return movement. The results showed that inter-individual variability of explicitly assessed biases of sensed hand position toward the cursor position was less in the adaptation condition than in the control condition. Conversely, no such changes were observed for the implicit measure of the bias of sensed hand position, revealing contrasting effects of adaptation on the explicit and implicit measures. These results suggest that biases of explicitly sensed hand position reflect sensory coupling of neural representations that are altered by visuomotor adaptation. In contrast, biases of implicitly sensed hand position reflect sensory coupling of neural representations that are unaffected by adaptation.

Muscular responses appear to be associated with existence of kinesthetic perception during combination of tendon co-vibration and motor imagery

The afferent inputs from peripheral sensory receptors and efferent signals from the central nervous system that underlie intentional movement can contribute to kinesthetic perception. Previous studies have revealed that tendon vibration to wrist muscles elicits an excitatory response-known as the antagonist vibratory response-in muscles antagonistic to the vibrated muscles. Therefore, the present study aimed to further investigate the effect of tendon vibration combined with motor imagery on kinesthetic perception and muscular activation. Two vibrators were applied to the tendons of the left flexor carpi radialis and extensor carpi radialis. When the vibration frequency was the same between flexors and extensors, no participant perceived movement and no muscle activity was induced. When participants imagined flexing their wrists during tendon vibration, the velocity of perceptual flexion movement increased. Furthermore, muscle activity of the flexor increased only during motor imagery. These results demonstrate that kinesthetic perception can be induced during the combination of motor imagery and co-vibration, even with no experience of kinesthetic perception from an afferent input with co-vibration at the same frequency. Although motor responses were observed during combined co-vibration and motor imagery, no such motor responses were recorded during either co-vibration alone or motor imagery alone, suggesting that muscular responses during the combined condition are associated with kinesthetic perception. Thus, the present findings indicate that kinesthetic perception is influenced by the interaction between afferent input from muscle spindles and the efferent signals that underlie intentional movement. We propose that the physiological behavior resulting from kinesthetic perception affects the process of modifying agonist muscle activity, which will be investigated in a future study.

Specific brain activation patterns associated with two neuromuscular electrical stimulation protocols

The influence of neuromuscular electrical stimulation (NMES) parameters on brain activation has been scarcely investigated. We aimed at comparing two frequently used NMES protocols - designed to vary in the extent of sensory input. Whole-brain functional magnetic resonance imaging was performed in sixteen healthy subjects during wide-pulse high-frequency (WPHF, 100 Hz–1 ms) and conventional (CONV, 25 Hz–0.05 ms) NMES applied over the triceps surae. Each protocol included 20 isometric contractions performed at 10% of maximal force. Voluntary plantar flexions (VOL) were performed as control trial. Mean force was not different among the three protocols, however, total current charge was higher for WPHF than for CONV. All protocols elicited significant activations of the sensorimotor network, cerebellum and thalamus. WPHF resulted in lower deactivation in the secondary somatosensory cortex and precuneus. Bilateral thalami and caudate nuclei were hyperactivated for CONV. The modulation of the NMES parameters resulted in differently activated/deactivated regions related to total current charge of the stimulation but not to mean force. By targeting different cerebral brain regions, the two NMES protocols might allow for individually-designed rehabilitation training in patients who can no longer execute voluntary movements.

The biology of skin wetness perception and its implications in manual function and for reproducing complex somatosensory signals in neuroprosthetics

Our perception of skin wetness is generated readily, yet humans have no known receptor (hygroreceptor) to signal this directly. It is easy to imagine the sensation of water running over our hands or the feel of rain on our skin. The synthetic sensation of wetness is thought to be produced from a combination of specific skin thermal and tactile inputs, registered through thermoreceptors and mechanoreceptors, respectively. The present review explores how thermal and tactile afference from the periphery can generate the percept of wetness centrally. We propose that the main signals include information about skin cooling, signaled primarily by thinly myelinated thermoreceptors, and rapid changes in touch, through fast-conducting, myelinated mechanoreceptors. Potential central sites for integration of these signals, and thus the perception of skin wetness, include the primary and secondary somatosensory cortices and the insula cortex. The interactions underlying these processes can also be modeled to aid in understanding and engineering the mechanisms. Furthermore, we discuss the role that sensing wetness could play in precision grip and the dexterous manipulation of objects. We expand on these lines of inquiry to the application of the knowledge in designing and creating skin sensory feedback in prosthetics. The addition of real-time, complex sensory signals would mark a significant advance in the use and incorporation of prosthetic body parts for amputees in everyday life.NEW & NOTEWORTHY Little is known about the underlying mechanisms that generate the perception of skin wetness. Humans have no specific hygroreceptor, and thus temperature and touch information combine to produce wetness sensations. The present review covers the potential mechanisms leading to the perception of wetness, both peripherally and centrally, along with their implications for manual function. These insights are relevant to inform the design of neuroengineering interfaces, such as sensory prostheses for amputees.

Localization of Impaired Kinesthetic Processing Post-stroke

Kinesthesia is our sense of limb motion, and allows us to gauge the speed, direction, and amplitude of our movements. Over half of stroke survivors have significant impairments in kinesthesia, which leads to greatly reduced recovery and function in everyday activities. Despite the high reported incidence of kinesthetic deficits after stroke, very little is known about how damage beyond just primary somatosensory areas affects kinesthesia. Stroke provides an ideal model to examine structure-function relationships specific to kinesthetic processing, by comparing lesion location with behavioral impairment. To examine this relationship, we performed voxel-based lesion-symptom mapping and statistical region of interest analyses on a large sample of sub-acute stroke subjects (N = 142) and compared kinesthetic performance with stroke lesion location. Subjects with first unilateral, ischemic stroke underwent neuroimaging and a comprehensive robotic kinesthetic assessment (~9 days post-stroke). The robotic exoskeleton measured subjects' ability to perform a kinesthetic mirror-matching task of the upper limbs without vision. The robot moved the stroke-affected arm and subjects' mirror-matched the movement with the unaffected arm. We found that lesions both within and outside primary somatosensory cortex were associated with significant kinesthetic impairments. Further, sub-components of kinesthesia were associated with different lesion locations. Impairments in speed perception were primarily associated with lesions to the right post-central and supramarginal gyri whereas impairments in amplitude of movement perception were primarily associated with lesions in the right pre-central gyrus, anterior insula, and superior temporal gyrus. Impairments in perception of movement direction were associated with lesions to bilateral post-central and supramarginal gyri, right superior temporal gyrus and parietal operculum. All measures of impairment shared a common association with damage to the right supramarginal gyrus. These results suggest that processing of kinesthetic information occurs beyond traditional sensorimotor areas. Additionally, this dissociation between kinesthetic sub-components may indicate specialized processing in these brain areas that form a larger distributed network.

Optimal visuotactile integration for velocity discrimination of self-hand movements

Illusory hand movements can be elicited by a textured disk or a visual pattern rotating under one's hand, while proprioceptive inputs convey immobility information (Blanchard C, Roll R, Roll JP, Kavounoudias A. PLoS One 8: e62475, 2013). Here, we investigated whether visuotactile integration can optimize velocity discrimination of illusory hand movements in line with Bayesian predictions. We induced illusory movements in 15 volunteers by visual and/or tactile stimulation delivered at six angular velocities. Participants had to compare hand illusion velocities with a 5°/s hand reference movement in an alternative forced choice paradigm. Results showed that the discrimination threshold decreased in the visuotactile condition compared with unimodal (visual or tactile) conditions, reflecting better bimodal discrimination. The perceptual strength (gain) of the illusions also increased: the stimulation required to give rise to a 5°/s illusory movement was slower in the visuotactile condition compared with each of the two unimodal conditions. The maximum likelihood estimation model satisfactorily predicted the improved discrimination threshold but not the increase in gain. When we added a zero-centered prior, reflecting immobility information, the Bayesian model did actually predict the gain increase but systematically overestimated it. Interestingly, the predicted gains better fit the visuotactile performances when a proprioceptive noise was generated by covibrating antagonist wrist muscles. These findings show that kinesthetic information of visual and tactile origins is optimally integrated to improve velocity discrimination of self-hand movements. However, a Bayesian model alone could not fully describe the illusory phenomenon pointing to the crucial importance of the omnipresent muscle proprioceptive cues with respect to other sensory cues for kinesthesia.