Selective impairment of sensorimotor representations following short-term upper-limb immobilization

How pain and body representations transform each other: A narrative review

Pain, as a multidimensional and subjective experience, intertwines with various aspects of body representation, involving sensory, affective and motivational components. This review explores the bidirectional relationship between pain and body representations, emphasizing the impact of the sense of ownership on pain perception, the transformative impact of pain on motor imagery, the effects associated with vicarious pain perception on body representations and the role of pain in the maintenance of body representations in specific clinical conditions. Literature indicates complex interactions between pain and body representations, with the sense of ownership inducing analgesic effects in some cases and hyperalgesia in others, contingent upon factors such as the appearance of the affected limb. Pain sensations inform the body on which actions might be executed without harm, and which are potentially dangerous. This information impacts on motor imagery too, showing reduced motor imagery and increased reaction times in tasks where motor imagery involves the painful body parts. Finally, contrary to the conventional view, according to which pain impairs body representation, evidence suggests that pain can serve as an informative somatosensory index, preserving or even enhancing the representation of the absent or affected body parts. This bidirectional relationship highlights the dynamic and multifaceted nature of the interplay between pain and body representations, offering insights into the adaptive nature of the central nervous system in response to perceived bodily states.

Arm cooling selectively impacts sensorimotor control

The benefits of cold have long been recognized in sport and medicine. However, it also brings costs, which have more rarely been investigated, notably in terms of sensorimotor control. We hypothesized that, in addition to peripheral effects, cold slows down the processing of proprioceptive cues, which has an impact on both feedback and feedforward control. We therefore compared the performances of participants whose right arm had been immersed in either cold water (arm temperature: 14°C) or lukewarm water (arm temperature: 34°C). In experiment 1, we administered a Fitts's pointing task and performed a kinematic analysis to determine whether sensorimotor control processes were affected by the cold. Results revealed 1) modifications in late kinematic parameters, suggesting changes in the use of proprioceptive feedback, and 2) modifications in early kinematic parameters, suggesting changes in action representations and/or feedforward processes. To explore our hypothesis further, we ran a second experiment in which no physical movement was involved, and thus no peripheral effects. Participants were administrated a hand laterality task, known to involve implicit motor imagery and assess the internal representation of the hand. They were shown left- and right-hand images randomly displayed in different orientations in the picture plane and had to identify as quickly and as accurately as possible whether each image was of the left hand or the right hand. Results revealed slower responses and more errors when participants had to mentally rotate the cooled hand in the extreme orientation of 160°, further suggesting the impact of cold on action representations.NEW & NOTEWORTHY We investigated how arm cooling modulates sensorimotor representations and sensorimotor control. Arm cooling induced changes in early kinematic parameters of pointing, suggesting an impact on feedforward processes or hand representation. Arm cooling induced changes in late kinematic parameters of pointing, suggesting an impact on feedback processes. Arm cooling also affected performance on a hand laterality task, suggesting that action representations were modified.

Effects of short-term hand immobilization on anticipatory mechanism for tool use

The short-term immobilization of a limb such as the right arm can impair sensorimotor mechanisms, which in turn reduces motor control of this arm. However, it is not known whether immobilization also impairs the anticipatory mechanism for tool use without actual enactment. In two experiments, we asked participants to judge how they would use a tool in a particular environment (e.g., "Take the pencil to write on a sheet of paper"). Prior to this tool-use judgment task, some participants had been immobilized (right arm) for 24 h. Results revealed that compared to controls, immobilized participants performed more poorly on the tool-use judgment task (accuracy and response time) as well as in a manual dexterity task. As our tool-use judgment task involved anticipating the expected perceptual effect of using a tool to achieve an environmental goal (e.g., writing on a sheet of paper), our data are discussed in line with theories of motor control (e.g., ideomotor theory) that emphasize the expected perceptual consequences of the action.

Distorted body schema after mastectomy with immediate breast reconstruction: a 4-month follow up study

Background

After breast cancer, some patients report residual pain-related upper limb disability without physical impairment. Although pain and altered proprioception are known to affect the working body schema (WBS), there is little available evidence investigating the WBS of breast cancer survivors (BrCS). WBS-body representations in the brain-affect the "neuromatrix" that modulates pain sensitivity and the threshold for threatening stimuli. The aim of this study was to investigate whether WBS was disrupted after mastectomy with immediate breast reconstruction (IBR) for breast cancer and whether pain and proprioceptive changes affected WBS.

Methods

Thirty-five BrCS participated in the 4-month follow-up study. They were observed at 1 and 4 months postoperatively. The main outcome measures were the left right judgement test (LRJT) results, absolute angle error, pectoralis minor length index (PMI), pain, and Quick-Disabilities of the Arm, Shoulder, and Hand (Q-DASH) score. They were measured at each observation, and parametric tests were performed to identify the nature of WBS.

Results

Both the reaction time and accuracy of the hand LRJT were poorer than those of the foot and back LRJT (p < 0.001). The hand LRJT reaction time and accuracy were unchanged over the total follow-up period (p = 0.77 and p = 0.47, respectively). There was a weak correlation between the LRJT reaction time and PMI (r = -0.26, p = 0.07), pain severity (r = 0.37, p = 0.02), and Q-DASH score (r = 0.37, p = 0.02). There was also a weak correlation between LRJT accuracy and Q-DASH score (r = -0.31, p = 0.04). The LRJT accuracy of BrCS who underwent surgery on their dominant side was higher than that of BrCS who underwent surgery on their non-dominant side (p = 0.002). Regression analysis found a weak but significant relationship between the early hand LRJT results and late pain severity (adjusted R² = 0.179, p = 0.007). A similar relationship was found between early hand LRJT results and Q-DASH score (adjusted R² = 0.099, p = 0.039).

Conclusion

To the best of our knowledge, this is the first study providing the nature of WBS after mastectomy with IBR. In this population, it is necessary to postoperatively preserve WBS integrity for pain and upper limb disability.

Hand laterality recognition in distal radius and/or ulna fracture

INTRODUCTION

Hand laterality, an important ability to determine the orientation of a limb is common to get affected after short term immobilization. Distal radius and/or ulna fracture is a commonly encountered fracture resulting from upper-limb trauma. Conservative treatment using closed reduction and plaster cast application to immobilize the joint remains choice of treatment over surgery in the treatment of these fractures. There is a paucity of literature reporting impairment in hand laterality after long term immobilization as commonly performed in patients with distal radius and/or ulna fractures. Understanding effect of immobilization on hand laterality in distal-end radius/ulna fractures warranted present investigation.

PURPOSE

To evaluate hand laterality based on the accuracy and response time for hand determination after plaster cast removal in distal radius and/or ulna fracture.

STUDY DESIGN

Prospective cross sectional study.

METHODOLOGY

Subjects (n = 60, age range = 40-59 years, females (n) = 28 and males (n) = 32) were shown 24 real-hand images with various degrees of angular rotation and instructed to identify the hand as left and/or right. Accuracy (% correctly identified) and Response time (milliseconds to identify left or right hand in the image) of motor imagery during hand laterality task were recorded. Pain intensity before and after the hand laterality task were noted using Visual Analogue Scale. Repeated measures of ANOVA and t tests were used to analyze the accuracy and response times among two groups.

RESULTS

The experimental group showed significantly (P < .05) lower accuracy and longer response time as compared to the control group. No significant difference in the accuracy and response time were noted in the immobilization of the dominant and the non-dominant hand within the experimental group (P > .05). Also, there was no change in pain pre- to post-hand laterality task.

CONCLUSION

Findings of this study could aid in enhancing the understanding of post-immobilization effect on hand laterality and open new arenas for assessment and rehabilitation of distal-end radius and/or ulna fractures where immobilization is the principal treatment.

Imagined paralysis reduces motor cortex excitability

Mental imagery is a powerful capability that engages similar neurophysiological processes that underlie real sensory and motor experiences. Previous studies show that motor cortical excitability can increase during mental imagery of actions. In this study, we focused on possible inhibitory effects of mental imagery on motor functions. We assessed whether imagined arm paralysis modulates motor cortical excitability in healthy participants, as measured by motor evoked potentials (MEPs) of the hand induced by near-threshold transcranial magnetic stimulation (TMS) over the primary motor cortex hand area. We found lower MEP amplitudes during imagined arm paralysis when compared to imagined leg paralysis or baseline stimulation without paralysis imagery. These results show that purely imagined bodily constraints can selectively inhibit basic motor corticospinal functions. The results are discussed in the context of motoric embodiment/disembodiment.

The Impact of Context on EEG Motor Imagery Neurofeedback and Related Motor Domains

Neurofeedback (NF) is a versatile non-invasive neuromodulation technique. In combination with motor imagery (MI), NF has considerable potential for enhancing motor performance or supplementing motor rehabilitation. However, not all users achieve reliable NF control. While research has focused on various brain signal properties and the optimisation of signal processing to solve this issue, the impact of context, i.e. the conditions in which NF motor tasks occur, is comparatively unknown. We review current research on the impact of context on MI NF and related motor domains. We identify long-term factors that act at the level of the individual or of the intervention, and short-term factors, with levels before/after and during a session. The reviewed literature indicates that context plays a significant role. We propose considering context factors as well as within-level and across-level interactions when studying MI NF.

Left/right discrimination is not impaired in people with unilateral chronic Achilles tendinopathy

OBJECTIVE

Impaired left/right discrimination of an affected body part has been observed in various chronic pain states. This study aimed to examine whether people with unilateral chronic Achilles tendinopathy also present with impaired left/right discrimination.

DESIGN

Cross-sectional study.

METHODS

Nineteen runners with persistent unilateral Achilles tendinopathy and 19 matched healthy volunteers performed a left/right discrimination task in a laboratory setting. Participants were shown pictures of feet, hands and Shepard-Metzler figures and were asked to decide as accurately and as fast as possible whether the body part belonged to the left or right side of the body, or whether the Shepard-Metzler figures were rotated or mirrored. Performance was evaluated in terms of accuracy and response time. Data were analysed with mixed-design ANOVAs.

RESULTS

The decline in left/right discrimination ability at group level, if present, between affected and unaffected side, or compared to healthy participants, was negligible for both accuracy (<1.5%) and response time (<50 ms). There was no significant effect of side (affected versus unaffected side) or group (people with Achilles tendinopathy versus healthy) for accuracy (p > 0.36) or response time (p > 0.69).

CONCLUSIONS

People with Achilles tendinopathy recognised the affected side as accurately and as fast as the non-affected side and their performance was comparable to healthy participants. The absence of impaired left/right discrimination despite the chronicity of the condition may be attributable to the typical intermittent nature of Achilles tendinopathy pain and/or maintained sports activity.

Motor imagery and action observation following immobilization-induced hypoactivity: a narrative review

BACKGROUND

In sports, the risk of pathology or event that leads to an injury, a cessation of practice or even to an immobilization is high. The subsequent reduction of physical activity, or hypoactivity, induces neural and muscular changes that adversely affect motor skills and functional motor rehabilitation. Because the implementation of physical practice is difficult, if not impossible, during and immediately following injury or immobilization, complementary techniques have been proposed to minimize the deleterious impact of hypoactivity on neuromuscular function.

OBJECTIVE

The current narrative review aimed to discuss the contributions of motor imagery and action observation, which enhance motor (re)learning and induce neural adaptations in both healthy individuals and injured athletes.

METHODS

Online literature research for studies of the effects of motor imagery, action observation and their combination on hypoactivity, extracting relevant publications within the last decade (2009-2020).

RESULTS

From published studies and the authors' knowledge of both motor imagery and action observation, some elements are provided for developing applied protocols during and after the immobilization period. Such interventions consist of associating congruent action observation with kinesthetic motor imagery of different movements, organized in increasing difficulty. The aim is to maintain motor functions and promote motor relearning by activating sensorimotor cortical areas and corticomotor pathways of the injured effector.

CONCLUSION

This narrative review supports the implementation of combined motor imagery and action observation protocols in the context of sports rehabilitation.

Short-term upper limb immobilisation impairs grasp representation

The present experiment aimed to gain more information on the effect of limb nonuse on the cognitive level of actions and, more specifically, on the content of the motor programme used for grasping an object. For that purpose, we used a hand-grasping laterality task that is known to contain concrete information on manipulation activity. Two groups participated in the experiment: an immobilised group, including participants whose right hand and arm were fixed with a rigid splint and an immobilisation vest for 24 hr, and a control group, including participants who did not undergo the immobilisation procedure. The main results confirmed the slowdown of sensorimotor processes, which is highlighted in the literature, with slower response times when the participants identified the laterality of hand images that corresponded to the immobilised hand. Importantly, the grip-precision effect, highlighted by slower response times for hands grasping a small sphere versus a large sphere, is impaired by 24 hr of limb nonuse. Overall, this study provided additional evidence of the disengagement of sensorimotor processes due to a short period of limb immobilisation.

Altered sensorimotor representations after recovery from peripheral nerve damage in neuralgic amyotrophy

Neuralgic amyotrophy is a common peripheral nerve disorder caused by acute autoimmune inflammation of the brachial plexus. Subsequent weakness of the stabilizing shoulder muscles leads to compensatory strategies and abnormal motor control of the shoulder. Despite recovery of peripheral nerves and muscle strength over time, motor dysfunction often persists. Suboptimal motor recovery has been linked to maladaptive changes in the central motor system in several nervous system disorders. We therefore hypothesized that neuralgic amyotrophy patients with persistent motor dysfunction may have altered cerebral sensorimotor representations of the affected upper limb. To test this hypothesis, 21 neuralgic amyotrophy patients (mean age 45 ± 12 years, 5 female) with persistent lateralized symptoms in the right upper limb and 20 age- and sex-matched healthy controls, all right-handed, performed a hand laterality judgement task in a cross-sectional comparison. Previous evidence has shown that to solve this task, subjects rely on sensorimotor representations of their own upper limb, using a first-person imagery perspective without actual motor execution. This enabled us to investigate altered central sensorimotor representations while controlling for altered motor output and altered somatosensory afference. We found that neuralgic amyotrophy patients were specifically less accurate for laterality judgments of their affected right limb, as compared to healthy controls. There were no significant group differences in reaction times. Both groups used a first-person imagery perspective, as evidenced by changes in reaction times as a function of participants' own arm posture. We conclude that cerebral sensorimotor representations of the affected upper limb are altered in neuralgic amyotrophy patients. This suggests that maladaptive central neuroplasticity may occur in response to peripheral nerve damage, thereby contributing to motor dysfunction. Therapies focused on altering cerebral sensorimotor representations may help to treat peripheral nerve disorders such as neuralgic amyotrophy.

Beyond Jeannerod's motor simulation theory: An approach for improving post-traumatic motor rehabilitation

This paper depicts an approach aiming to allow individuals with orthopedic trauma injuries to optimize recovery and safely return to daily life. The core of this approach is motor simulation, used in complement to conventional physical rehabilitation methods. This paper provides recent scientific insights on the basis of motor simulation, discusses benefits of this approach in motor rehabilitation, and provides applied perspectives.

A functional limitation to the lower limbs affects the neural bases of motor imagery of gait

Studies on athletes or neurological patients with motor disorders have shown a close link between motor experience and motor imagery skills. Here we evaluated whether a functional limitation due to a musculoskeletal disorder has an impact on the ability to mentally rehearse the motor patterns of walking, an overlearned and highly automatic behaviour. We assessed the behavioural performance (measured through mental chronometry tasks) and the neural signatures of motor imagery of gait in patients with chronic knee arthrosis and in age-matched, healthy controls. During fMRI, participants observed (i) stationary or (ii) moving videos of a path in a park shown in the first-person perspective: they were asked to imagine themselves (i) standing on or (ii) walking along the path, as if the camera were “their own eyes” (gait imagery (GI) task). In half of the trials, participants performed a dynamic gait imagery (DGI) task by combining foot movements with GI. Behavioural tests revealed a lower degree of isochrony between imagined and performed walking in the patients, indicating impairment in the ability to mentally rehearse gait motor patterns. Moreover, fMRI showed widespread hypoactivation during GI in motor planning (premotor and parietal) brain regions, the brainstem, and the cerebellum. Crucially, the performance of DGI had a modulatory effect on the patients and enhanced activation of the posterior parietal, brainstem, and cerebellar regions that the healthy controls recruited during the GI task. These findings show that functional limitations of peripheral origin may impact on gait motor representations, providing a rationale for cognitive rehabilitation protocols in patients with gait disorders of orthopaedic nature. The DGI task may be a suitable tool in this respect.

•

Patients with chronic knee arthrosis show impairment in gait motor imagery

•

Impairment is selective for gait and paralleled by hypoactivation in premotor areas

•

Peripheral limitation of lower limb movements affects central gait motor control

•

Dynamic motor imagery favours the recruitment of a motor strategy during imagery

•

Mental motor training might help to restore gait control in orthopaedic patients