On the role of imagery modalities on motor learning

Learning motor actions via imagery-perceptual or motor learning?

It is well accepted that repeatedly imagining oneself acting without any overt behavior can lead to learning. The prominent theory accounting for why imagery practice is effective, motor simulation theory, posits that imagined action and overt action are functionally equivalent, the exception being activation of the end effector. If, as motor simulation theory states, one can compile the goal, plan, motor program and outcome of an action during imagined action similar to overt action, then learning of novel skills via imagery should proceed in a manner equivalent to that of overt action. While the evidence on motor simulation theory is both plentiful and diverse, it does not explicitly account for differences in neural and behavioural findings between imagined and overt action. In this position paper, we briefly review theoretical accounts to date and present a perceptual-cognitive theory that accounts for often observed outcomes of imagery practice. We suggest that learning by way of imagery reflects perceptual-cognitive scaffolding, and that this 'perceptual' learning transfers into 'motor' learning (or not) depending on various factors. Based on this theory, we characterize consistently reported learning effects that occur with imagery practice, against the background of well-known physical practice effects and show that perceptual-cognitive scaffolding is well-suited to explain what is being learnt during imagery practice.

Effects of Mirror Neurons-Based Rehabilitation Techniques in Hand Injuries: A Systematic Review and Meta-Analysis

Background: Hand trauma requires specific rehabilitation protocol depending on the different structures involved. According to type of surgical intervention, and for monitoring pain and edema, post-operative rehabilitation of a hand that has experienced trauma involves different timings for immobilization. Several protocols have been used to reduce immobilization time, and various techniques and methods are adopted, depending on the structures involved. Objective: To measure the effects of mirror neurons-based rehabilitation techniques in hand injuries throughout a systematic review and meta-analysis. Methods: The protocol was accepted in PROSPERO database. A literature search was conducted in Cinahl, Scopus, Medline, PEDro, OTseeker. Two authors independently identified eligible studies, based on predefined inclusion criteria, and extracted the data. RCT quality was assessed using the JADAD scale. Results: Seventy-nine suitable studies were screened, and only eleven were included for qualitative synthesis, while four studies were selected for quantitative analysis. Four studies were case reports/series, and seven were RCTs. Nine investigate the effect of Mirror Therapy and two the effect of Motor Imagery. Quantitative analyses revealed Mirror Therapy as effective for hand function recovery (mean difference = −14.80 95% Confidence Interval (CI) = −17.22, −12.38) (p < 0.00001) in the short term, as well as in long follow-up groups (mean difference = −13.11 95% Confidence Interval (CI) = −17.53, −8.69) (p < 0.00001). Clinical, but not statistical, efficacy was found for manual dexterity (p = 0.15), while no benefit was reported for range of motion. Conclusions: Mirror neurons-based rehabilitation techniques, combined with conventional occupational and physical therapy, can be a useful approach in hand trauma. Mirror therapy seems to be effective for hand function recovery, but, for motor imagery and action observation, there is not sufficient evidence to recommend its use. Further research on the efficacy of the mirror neurons-based technique in hand injury is recommended.

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.

Imagining handwriting movements in a usual or unusual position: effect of posture congruency on visual and kinesthetic motor imagery

Motor imagery has been used in training programs to improve the performance of motor skills. Handwriting movement may benefit from motor imagery training. To optimize the efficacy of this kind of training, it is important to identify the factors that facilitate the motor imagery process for handwriting movements. Several studies have shown that motor imagery is more easily achieved when there is maximum compatibility between the actual posture and the imagined movement. We, therefore, examined the effect of posture congruency on visual and kinesthetic motor imagery for handwriting movements. Adult participants had to write and imagine writing a sentence by focusing on the evocation of either the kinesthetic or visual consequences of the motion. Half the participants performed the motor imagery task in a congruent posture (sitting with a hand ready for writing), and half in an incongruent one (standing with arms crossed behind the back and fingers spread wide). The temporal similarity between actual and imagined movement times and the vividness of the motor imagery were evaluated. Results revealed that temporal similarity was stronger in the congruent posture condition than in the incongruent one. Furthermore, in the incongruent posture condition, participants reported greater difficulty forming a precise kinesthetic motor image of themselves writing than a visual image, whereas no difference was observed in the congruent posture condition. Taken together, our results show that postural information is taken into account during the mental simulation of handwriting movements. The implications of these findings for guiding the design of motor imagery training are discussed.

Does the Improvement of Position Sense Following Motor Imagery Practice Vary as a Function of Age and Time of Day?

The effectiveness of motor imagery practice is known to depend on age and on the ability to form motor images. In the same individual, motor imagery quality changes during the day, being better late in the morning for older adults and in the afternoon for younger adults. Does this mean that motor imagery practice should be done at specific time of the day depending on the age of participants to maximize motor learning? To examine whether the effect of motor imagery practice varies as a function of time of day and age, the authors used an arm configuration reproduction task and measured position sense accuracy before and after 135 kinesthetic motor imagery trials. Younger and older participants were randomly assigned to either a morning or an afternoon session. Data showed that the accuracy for reproducing arm configurations improved following imagery practice regardless of time of day for both younger and older adults. Moreover, the authors observed that the position sense was less accurate in the afternoon than in the morning in older participants (before and after motor imagery practice), while performance did not change during the day in younger participants. These results may have practical implications in motor learning and functional rehabilitation programs. They highlight the effectiveness of motor imagery practice for movement accuracy in both younger and older adults regardless of time of day. By contrast, they reveal that the assessment of position sense requires that the time of day be taken into account when practitioners want to report on the older patients' progress without making any mistakes.

The specificity of practice hypothesis in goal-directed movements: visual dominance or proprioception neglect?

The study aimed to examine whether modifying the proprioceptive feedback usually associated with a specific movement would decrease the dominance of visual feedback and/or decrease, which appears to be the neglect of proprioceptive feedback in ensuring the accuracy of goal-directed movements. We used a leg positioning recall task and measured the recall error after 15 and 165 acquisition trials performed with both vision and proprioception or proprioception only, under either a normal or a modified proprioception condition (i.e., with a 1-kg load attached to the participants' ankle). Participant learning was evaluated in transfer with proprioception only. In support of the specificity of practice hypothesis, the recall errors in acquisition were significantly smaller when practice occurred with both vision and proprioception, in either the loaded or the unloaded leg condition, and they increased significantly in transfer when vision was withdrawn. An important finding of the study highlighted that withdrawing vision after 165 acquisition trials had less deleterious effects on the recall errors when practice occurred under the loaded leg condition. Under that modified condition, recall errors in transfer were similar when practice occurred with and without vision, whereas larger errors were observed following practice with vision under the normal proprioceptive condition. Overall, these results highlighted the dominance of vision in ensuring accurate leg positioning recall and revealed that the dominance of vision is such that the processing of proprioceptive feedback may be neglected. Importantly, modifying the proprioceptive feedback has the advantage of reducing what appears to be the neglect of proprioceptive information when movement execution occurs in a visuo-proprioceptive context. Practical considerations for rehabilitation are discussed at the end of the manuscript.

Effects of mental practice in novice learners in a serial positioning skill acquisition

The effects of mental practice in novices were investigated. University students (N = 60) performed a serial aiming task, distributed in 5 groups of 12: mental practice, physical practice, mental-physical practice (first mental then physical practice), physical-mental practice (first physical then mental practice), and a control group that only performed the tests. Participants transported three tennis balls among six containers in a pre-established sequence in a target time. In the acquisition phase and retention test (24 hr. later), the task was the same; in the transfer test, 5 min. after the acquisition phase, sequence and time changed. Six trials were performed in the acquisition phase, and each test consisted of 9 trials. The performance measures were absolute error, constant error, and variable error; a t test and a two-way ANOVA were used to compare the acquisition phase and tests, respectively. Physical practice and both groups of combined conditions presented better performance in tests than the mental practice and control groups. Mental practice without motor experience in the task did not improve motor learning. Prior physical performance is desirable before conducting mental practice.

Neural activation and functional connectivity during motor imagery of bimanual everyday actions

Bimanual actions impose intermanual coordination demands not present during unimanual actions. We investigated the functional neuroanatomical correlates of these coordination demands in motor imagery (MI) of everyday actions using functional magnetic resonance imaging (fMRI). For this, 17 participants imagined unimanual actions with the left and right hand as well as bimanual actions while undergoing fMRI. A univariate fMRI analysis showed no reliable cortical activations specific to bimanual MI, indicating that intermanual coordination demands in MI are not associated with increased neural processing. A functional connectivity analysis based on psychophysiological interactions (PPI), however, revealed marked increases in connectivity between parietal and premotor areas within and between hemispheres. We conclude that in MI of everyday actions intermanual coordination demands are primarily met by changes in connectivity between areas and only moderately, if at all, by changes in the amount of neural activity. These results are the first characterization of the neuroanatomical correlates of bimanual coordination demands in MI. Our findings support the assumed equivalence of overt and imagined actions and highlight the differences between uni- and bimanual actions. The findings extent our understanding of the motor system and may aid the development of clinical neurorehabilitation approaches based on mental practice.

Best practice for motor imagery: a systematic literature review on motor imagery training elements in five different disciplines

BACKGROUND

The literature suggests a beneficial effect of motor imagery (MI) if combined with physical practice, but detailed descriptions of MI training session (MITS) elements and temporal parameters are lacking. The aim of this review was to identify the characteristics of a successful MITS and compare these for different disciplines, MI session types, task focus, age, gender and MI modification during intervention.

METHODS

An extended systematic literature search using 24 databases was performed for five disciplines: Education, Medicine, Music, Psychology and Sports. References that described an MI intervention that focused on motor skills, performance or strength improvement were included. Information describing 17 MITS elements was extracted based on the PETTLEP (physical, environment, timing, task, learning, emotion, perspective) approach. Seven elements describing the MITS temporal parameters were calculated: study duration, intervention duration, MITS duration, total MITS count, MITS per week, MI trials per MITS and total MI training time.

RESULTS

Both independent reviewers found 96% congruity, which was tested on a random sample of 20% of all references. After selection, 133 studies reporting 141 MI interventions were included. The locations of the MITS and position of the participants during MI were task-specific. Participants received acoustic detailed MI instructions, which were mostly standardised and live. During MI practice, participants kept their eyes closed. MI training was performed from an internal perspective with a kinaesthetic mode. Changes in MI content, duration and dosage were reported in 31 MI interventions. Familiarisation sessions before the start of the MI intervention were mentioned in 17 reports. MI interventions focused with decreasing relevance on motor-, cognitive- and strength-focused tasks. Average study intervention lasted 34 days, with participants practicing MI on average three times per week for 17 minutes, with 34 MI trials. Average total MI time was 178 minutes including 13 MITS. Reporting rate varied between 25.5% and 95.5%.

CONCLUSIONS

MITS elements of successful interventions were individual, supervised and non-directed sessions, added after physical practice. Successful design characteristics were dominant in the Psychology literature, in interventions focusing on motor and strength-related tasks, in interventions with participants aged 20 to 29 years old, and in MI interventions including participants of both genders. Systematic searching of the MI literature was constrained by the lack of a defined MeSH term.