Mental rotation of hands and objects in ageing and Parkinson’s disease: Implications for understanding motor imagery

Motor imagery (MI) supports motor learning and performance, having the potential to be a useful tool for neurorehabilitation. However, MI ability may be impacted by ageing and neurodegeneration, which could limit its therapeutic effectiveness. MI is often assessed through a hand laterality task (HLT), whereby laterality judgements are typically slower for hands presented at orientations corresponding to physically more difficult postures (a “biomechanical constraint” effect). Performance is also found to differ between back and palm views of the hand, suggesting the differential involvement of visual and sensorimotor strategies. While older adults are generally found to be slowed and show increased biomechanical effects, few studies have examined the effects of both ageing and Parkinson’s disease (PD).The present study compared healthy younger (YA), healthy older (OA) and PD groups on HLT performance from both palm and back views, as well as an object-based (letter) mental rotation task. OA and PD groups were slower than YA, particularly when judging laterality from the back view, and exhibited increased biomechanical constraint effects for the palm. While response times were generally similar between OA and PD groups, the PD group showed reduced accuracy in the back view. Moreover, object rotation was slower and less accurate only in the PD group. The results indicate that different mechanisms are involved in mental rotation of hands viewed from the back or palm, consistent with previous findings, and demonstrate particular effects of ageing and PD when judging the back view. Alongside findings from studies of explicit MI, this suggests a greater alteration of visual than kinaesthetic MI with ageing and neurodegeneration, with additional impairment of object-based visual imagery in PD. The findings are also discussed in relation to different perspectives in MI and the integration of visual and kinaesthetic representations.

Atypical influence of biomechanical knowledge in Complex Regional Pain Syndrome-Towards a different perspective on body representation

Part of the multifaceted pathophysiology of Complex Regional Pain syndrome (CRPS) has been ascribed to a lateralized maladaptive neuroplasticity in sensorimotor cortices, a finding that has been corroborated by behavioral studies indicating that CRPS patients indeed present difficulties in mentally representing their painful limb. Hand laterality judgment tasks (HLT) are widely used to measure such difficulties, with the laterality of hand stimuli corresponding to the affected hand judged more slowly than the one of hand stimuli corresponding to the unaffected hand. Importantly, the HLT is also regularly used in the rehabilitation of CRPS and other chronic pain disorders, with the aim to activate motor imagery and, consequently, restoring the cortical representation of the limb. The potential of these tasks to elicit motor imagery is thus critical to their use in therapy. Yet, the influence of the biomechanical constraints (BMC) on HLT reaction time, supposed to reflect the activation of motor imagery, is rarely verified. In the present study we investigated the influence of the BMC on the perception of hand postures and movements. The results of a first experiment, in which a HLT was used, showed that CRPS patients were significantly slower than controls in judging hand stimuli, whether or not the depicted hand corresponded to their affected hand, but that their performance did not differ from controls when they judged non-body stimuli. Results regarding reaction time patterns reflecting the BMC were inconclusive in CRPS and controls, questioning the validity of the task in activating motor imagery processes. In a second experiment we therefore directly investigated the influence of implicit knowledge of upper-limb BMC on perceptual judgments of hand movements with the apparent body movement perception task. Participants judge the perceived path of movement between two depicted hand positions, with only one of the two proposed paths that is biomechanically plausible. While the controls chose the biomechanically plausible path most of the time, CRPS patients did not, indicating that the perception and/or use of the BMC seems to be disturbed in CRPS. These findings show a non-lateralized body representation impairment in CRPS, which might be related to difficulties in using correct knowledge of the body's biomechanics. Most importantly however, our results, in agreement with previous studies, indicate that it seems highly challenging to measure motor imagery and the indexes of BMC with the classical HLT task, which has important implications for the rehabilitation of chronic pain with these tasks.

Development of Laterality and Bimanual Interference of Fine Motor Movements in Childhood and Adolescence

Drawing and handwriting are fine motor skills acquired during childhood. We analyzed the development of laterality by comparing the performance of the dominant with the nondominant hand and the effect of bimanual interference in kinematic hand movement parameters (speed, automation, variability, and pressure). Healthy subjects (n = 187, 6–18 years) performed drawing tasks with both hands on a digitizing tablet followed by performance in the presence of an interfering task of the nondominant hand. Age correlated positively with speed, automation, and pressure, and negatively with variability for both hands. As task complexity increased, differences between both hands were less pronounced. Playing an instrument had a positive effect on the nondominant hand. Speed and automation showed a strong association with lateralization. Bimanual interference was associated with an increase of speed and variability. Maturation of hand laterality and the extent of bimanual interference in fine motor tasks are age-dependent processes.

Feasibility of motor imagery and effects of activating and relaxing practice on autonomic functions in healthy young adults: A randomised, controlled, assessor-blinded, pilot trial

Introduction Motor imagery (MI) is the mental rehearsal of a motor task. Between real and imagined movements, a functional equivalence has been described regarding timing and brain activation. The primary study aim was to investigate the feasibility of MI training focusing on the autonomic function in healthy young people. Further aims were to evaluate participants’ MI abilities and compare preliminary effects of activating and relaxing MI on autonomic function and against controls. Methods A single-blinded randomised controlled pilot trial was performed. Participants were randomised to the activating MI (1), relaxing MI (2), or control (3) group. Following a MI familiarisation, they practiced home-based kinaesthetic MI for 17 minutes, 5 times/week for 2 weeks. Participants were called once for support. The primary outcome was the feasibility of a full-scale randomised controlled trial using predefined criteria. Secondary outcomes were participants’ MI ability using the Movement Imagery Questionnaire-Revised, mental chronometry tests, hand laterality judgement and semi-structured interviews, autonomic function. Results A total of 35 participants completed the study. The feasibility of a larger study was confirmed, despite 35% attrition related to the COVID-19 pandemic. Excellent MI capabilities were seen in participants, and significant correlations between MI ability measures. Interview results showed that participants accepted or liked both interventions. Seven major themes and insider recommendations for MI interventions emerged. No significant differences and negligible to medium effects were observed in MI ability or autonomic function between baseline and post-intervention measures or between groups. Conclusions Results showed that neither activating nor relaxing MI seems to change autonomic function in healthy individuals. Further adequately powered studies are required to answer open questions remaining from this study. Future studies should investigate effects of different MI types over a longer period, to rule out habituation and assess autonomic function at several time points and simultaneously with MI.

Motor imagery practice benefits during arm immobilization

Motor imagery (MI) is known to engage motor networks and is increasingly used as a relevant strategy in functional rehabilitation following immobilization, whereas its effects when applied during immobilization remain underexplored. Here, we hypothesized that MI practice during 11 h of arm-immobilization prevents immobilization-related changes at the sensorimotor and cortical representations of hand, as well as on sleep features. Fourteen participants were tested after a normal day (without immobilization), followed by two 11-h periods of immobilization, either with concomitant MI treatment or control tasks, one week apart. At the end of each condition, participants were tested on a hand laterality judgment task, then underwent transcranial magnetic stimulation to measure cortical excitability of the primary motor cortices (M1), followed by a night of sleep during which polysomnography data was recorded. We show that MI treatment applied during arm immobilization had beneficial effects on (1) the sensorimotor representation of hands, (2) the cortical excitability over M1 contralateral to arm-immobilization, and (3) sleep spindles over both M1s during the post-immobilization night. Furthermore, (4) the time spent in REM sleep was significantly longer, following the MI treatment. Altogether, these results support that implementing MI during immobilization may limit deleterious effects of limb disuse, at several levels of sensorimotor functioning.

The Body across the Lifespan: On the Relation between Interoceptive Sensibility and High-Order Body Representations

Background: Interoceptive information plays a pivotal role in building higher-order cognitive body representations (BR) that neuropsychological and neuroimaging evidence classifies as action-oriented (i.e., body schema) or non-action-oriented (i.e., visuo-spatial body map). This study aimed to explore the development of BR, considering the association with the interoceptive sensibility throughout the lifespan. Methods: Two hundred thirty-nine healthy participants divided into five age groups (7 to 8 years; 9 to 10 years; 18 to 40 years; 41 to 60 years; over 60 years) completed a self-report measure of interoceptive sensibility (the Self-Awareness Questionnaire; SAQ) and were given tasks assessing the two BR (action-oriented: hand laterality task; non-action-oriented: frontal body evocation task). Results: Both children (7–8 and 9–10 years) and older adults (over 60 years) performed worse than young (18–40 years) and middle-aged adults (41–60 years) in action- and non-action-oriented BR tasks. Moderation analyses showed that the SAQ score significantly moderated the relationship between age and action-oriented BR. Conclusions: The current results are consistent with inverted U-shaped developmental curves for action- and non-action-oriented BR. As an innovative aspect, the ability to mentally represent one’s own body parts in diverse states could be negatively affected by higher interoceptive sensibility levels in childhood and late adulthood.

The Relationship Between Internal Motor Imagery and Motor Inhibition in School-Aged Children: A Cross-Sectional Study

Functional equivalence hypothesis and motor-cognitive model both posit that motor imagery performance involves inhibition of overt physical movement and thus engages control processes. As motor inhibition in internal motor imagery has been fairly well studied in adults, the present study aimed to investigate the correlation between internal motor imagery and motor inhibition in children. A total of 73 children (7-year-olds: 23, 9-year-olds: 27, and 11-year-olds: 23) participated the study. Motor inhibition was assessed with a stop-signal task, and motor imagery abilities were measured with a hand laterality judgment task and an alphanumeric rotation task, respectively. Overall, for all age groups, response time in both motor imagery tasks increased with rotation angles. Moreover, all children’s response times in both tasks decreased with age, their accuracy increased with age, and their motor inhibition efficiency increased with age. We found a significant difference between 7-year-olds and 9-year-olds in the hand laterality judgment task, suggesting that the involvement of motor inhibition in internal motor imagery might change with age. Our results reveal the underlying processes of internal motor imagery development, and furthermore, provide practical implications for movement rehabilitation of children.

The Body Across Adulthood: On the Relation Between Interoception and Body Representations

Interoceptive information plays a pivotal role in building body representations (BR), but the association between interoception and the different types of BR in healthy individuals has never been systematically investigated. Thus, this study aimed to explore the association between BR and interoceptive sensibility (IS) throughout adulthood. One hundred thirty-seven healthy participants (50 aged from 18 to 40 years old; 50 aged from 41 to 60 years old; and 37 over 60 years old) were given a self-report tool for assessing IS (the Self-Awareness Questionnaire; SAQ), and a specific battery including tasks evaluating three different BR (i.e., the body schema, using the Hand Laterality Task; the body structural representation, using the Frontal Body Evocation task, FBE; and body semantics, using the Object-Body Part Association Task) as well as control tasks (i.e., tasks with non-body stimuli). The older age group (aged over 60 years old) showed lower performances on the tasks probing the body schema and body structural representation than younger groups (aged 18 to 40 and 41 to 60 years old). More interestingly, worse performances on a task assessing the body schema were significantly associated with higher IS with older age, suggesting that higher awareness of one’s inner body sensations would decrease the plasticity of this BR. These findings are interpreted according to the neuropsychological model of BR development and the effects of aging on the brain.

A Study of Embodiment and Its Relations with Body Awareness and Empathy

Objective: The embodiment theories have been an increasingly important perspective to understand the social mind, and the current study aims to demonstrate how embodiment is built up from the interoceptive states of the body and how it contributes to human empathy. Method: Forty-two participants with normal vision or corrected-to-normal vision completed the hand Laterality Judgement Task (LJT) and questionnaires on body awareness and empathy. Response accuracies and reaction times in LJT and self-report scores from body awareness and empathy quotient questionnaires were collected. Results: A Pearson’s correlation analysis revealed that body awareness scores correlated positively with empathy scores and a paired samples t-test showed that people who were self-described as having a white skin tone responded to hand stimuli of black skin tone more accurately than to hand stimuli of white skin tone. Conclusions: These findings suggest the important role of the awareness of internal body states in higher order social cognition, and that higher-level action simulation is a bidirectional process, as other mental representations. Limitations are discussed for the improvements in future studies.