Modeling the Maturation of Grip Selection Planning and Action Representation: Insights from Typical and Atypical Motor Development

White matter organisation of sensorimotor tracts is associated with motor imagery in childhood

Despite the important role of motor imagery (MI) in motor development, our understanding of the contribution of white matter fibre properties to MI performance in childhood remains limited. To provide novel insight into the white matter correlates of MI performance, this study examined the association between white matter fibre properties and motor imagery performance in a sample of typically developing children. High angular diffusion weighted imaging data were collected from 22 typically developing children aged 6-14 years (12 female, MAge= 10.56). Implicit motor imagery performance was assessed using a mental hand rotation paradigm. The cerebellar peduncles and the superior longitudinal fasciculus were reconstructed using TractSeg, a semi-automated method. For each tract, white matter microstructure (fibre density, FD) and morphology (fibre bundle cross-section, FC) were estimated using Fixel-Based Analysis. Permutation-based inference testing and partial correlation analyses demonstrated that higher FC in the middle cerebellar peduncles was associated with better MI performance. Tract-based region of interest analyses showed that higher FC in the middle and superior cerebellar peduncles were associated with better MI performance. Results suggest that white matter connectivity along the cerebellar peduncles may facilitate MI performance in childhood. These findings advance our understanding of the neurobiological systems that underlie MI performance in childhood and provide early evidence for the relevance of white matter sensorimotor pathways to internal action representations.

Which outcomes are key to the pre-intervention assessment profile of a child with developmental coordination disorder? A systematic review and meta-analysis

BACKGROUND

Purpose of this study was to determine what key aspects of function should be incorporated to make up a pre-intervention assessment profile of a child with Developmental Coordination Disorder (DCD); more specifically, what aspects of functioning are implicated in DCD and what is their relative impact?

METHODS

A systematic review and meta-analysis were conducted, for which Pubmed, Web of Science, Scopus and Proquest were searched (last update: April 2023, PROSPERO: CRD42023461619). Case-control studies were included to determine point estimates for performances on field-based tests in different domains of functioning. Risk of bias was assessed, and level of evidence estimated. Random-effect meta-analyses were performed to calculate the pooled standardized mean differences for domains of functioning and subgrouping was done for clinically relevant subdomains. Heterogeneity was determined with I2.

RESULTS

121 papers were included for analyses. Data of 5 923 children with DCD were included (59.8% boys) and 23 619 Typically Developing (TD) children (45.8% boys). The mean (SD) age of the DCD group was 10.3y (1.2) and 9.3y (1.3) for the TD children. Moderate evidence was found for motor performance, executive functions, sensory processing and perceptions, cognitive functions and sports and leisure activities to be affected in children with DCD.

CONCLUSION

Differences between the two groups varied per domain of functioning. This emphasizes the diversity present within children with DCD and provides a rationale for explaining the heterogeneity in this patient group. Yet, results highlight the potential involvement of all these domains and call for clinicians to be alert not only to examine motor skill difficulties but also other aspects of function. Results indicate the need to develop an individualized pre-intervention multi-dimensional assessment profile for each child with DCD. It also supports the important role that clinicians play in an interdisciplinary team to tackle the difficulties encountered by children with DCD.

Upper Limb Kinematics of Handwriting among Children with and without Developmental Coordination Disorder

Background: Children with developmental coordination disorder (DCD) often experience difficulties with handwriting legibility and speed. This study investigates the relationship between handwriting and upper limb kinematics to characterize movement patterns of children with DCD and typically developing (TD) children. Methods: 30 children with and without DCD matched for age, gender, and parent education were compared across handwriting abilities using a standardized handwriting assessment of both copied and dictated tasks (A-A Handwriting). The 3D motion capture system (Qualysis) was used to analyze upper limb kinematics and characterize movement patterns during handwriting and contrasted with written output. Results: Children with DCD wrote fewer legible letters in both copying and dictation. Children with DCD also showed poor automatization of key writing concepts. Atypical wrist postures were associated with reduced legibility for children with DCD (F (1,27) 4.71, p = 0.04, p-η2 = 0.15); whereas for TD children, better legibility was associated with greater variations in movement speed, particularly of the wrist (rho = −0.578, p < 0.05). Conclusion: Results reflect different movement parameters influencing handwriting in children with DCD. An improved understanding of the movement characteristics during handwriting of these children may assist intervention design.

The role of the primary motor cortex in motor imagery: A theta burst stimulation study

While mentally simulated actions activate similar neural structures to overt movement, the role of the primary motor cortex (PMC) in motor imagery remains disputed. The aim of the study was to use continuous theta burst stimulation (cTBS) to modulate corticospinal activity to investigate the putative role of the PMC in implicit motor imagery in young adults with typical and atypical motor ability. A randomized, double blind, sham-controlled, crossover, offline cTBS protocol was applied to 35 young adults. During three separate sessions, adults with typical and low motor ability (developmental coordination disorder [DCD]), received active cTBS to the PMC and supplementary motor area (SMA), and sham stimulation to either the PMC or SMA. Following stimulation, participants completed measures of motor imagery (i.e., hand rotation task) and visual imagery (i.e., letter number rotation task). Although active cTBS significantly reduced corticospinal excitability in adults with typical motor ability, neither task performance was altered following active cTBS to the PMC or SMA, compared to performance after sham cTBS. These results did not differ across motor status (i.e., typical motor ability and DCD). These findings are not consistent with our hypothesis that the PMC (and SMA) is directly involved in motor imagery. Instead, previous motor cortical activation observed during motor imagery may be an epiphenomenon of other neurophysiological processes and/or activity within brain regions involved in motor imagery. This study highlights the need to consider multi-session theta burst stimulation application and its neural effects when probing the putative role of motor cortices in motor imagery.

Association between Motor Planning and the Frontoparietal Network in Children: An Exploratory Multimodal Study

OBJECTIVE

Evidence from adult literature shows the involvement of cortical grey matter areas of the frontoparietal lobe and the white matter bundle, the superior longitudinal fasciculus (SLF) in motor planning. This is yet to be confirmed in children.

METHOD

A multimodal study was designed to probe the neurostructural basis of childhood motor planning. Behavioural (motor planning), magnetic resonance imaging (MRI) and diffusion weighted imaging (DWI) data were acquired from 19 boys aged 8-11 years. Motor planning was assessed using the one and two colour sequences of the octagon task. The MRI data were preprocessed and analysed using FreeSurfer 6.0. Cortical thickness and cortical surface area were extracted from the caudal middle frontal gyrus (MFG), superior frontal gyrus (SFG), precentral gyrus (PcG), supramarginal gyrus (SMG), superior parietal lobe (SPL) and the inferior parietal lobe (IPL) using the Desikan-Killiany atlas. The DWI data were preprocessed and analysed using ExploreDTI 4.8.6 and the white matter tract, the SLF was reconstructed.

RESULTS

Motor planning of the two colour sequence was associated with cortical thickness of the bilateral MFG and left SFG, PcG, IPL and SPL. The right SLF was related to motor planning for the two colour sequence as well as with the left cortical thickness of the SFG.

CONCLUSION

Altogether, morphology within frontodorsal circuity, and the white matter bundles that support communication between them, may be associated with individual differences in childhood motor planning.

Representational Processes of Actions Toward and Away from the Body

The aim of the present study was to investigate the role of mental representation processes during the planning, reaching, and use phases of actions with tools commonly used toward the body (TB, e.g., toothbrush) or away from the body (AB, e.g., pencil). In the first session, healthy participants were asked to perform TB (i.e., making circular movements with the toothbrush near the mouth) and AB (i.e., making circular movements with the pencil near the desk) actions both with (i.e., actual use) and without the tool in hand (i.e., the pantomime of tool use). In the second session, the same participants performed a series of mental rotation tasks involving body- (i.e., face and hands) and object-related (i.e., abstract lines) stimuli. The temporal and kinematic analysis of the motor actions showed that the time required to start the pantomimes (i.e., the planning phase) was shorter for the AB action than for the TB action. In contrast, the reaching phase lasted longer for the AB action than for the TB action. Furthermore, the TB pantomime was associated with the performance in the mental rotation of body-related stimuli, especially during the planning and reaching phases, whereas the AB pantomime was more related to the performance in the mental rotation of object-related stimuli, especially during the tool use phase. Thus, the results revealed that the direction of a goal-directed motor action influences the dynamics of the different phases of the motor action and can determine the type of mental images involved in the planning and execution of the action.

Real-time processes in the development of action planning

Across species and ages, planning multi-step actions is a hallmark of intelligence and critical for survival. Traditionally, researchers adopt a "top-down" approach to action planning by focusing on the ability to create an internal representation of the world that guides the next step in a multi-step action. However, a top-down approach does not inform on underlying mechanisms, so researchers can only speculate about how and why improvements in planning occur. The current study takes a "bottom-up" approach by testing developmental changes in the real-time, moment-to-moment interplay among perceptual, neural, and motor components of action planning using simultaneous video, motion-tracking, head-mounted eye tracking, and electroencephalography (EEG). Preschoolers (n = 32) and adults (n = 22) grasped a hammer with their dominant hand to pound a peg when the hammer handle pointed in different directions. When the handle pointed toward their non-dominant hand, younger children ("nonadaptive planners") used a habitual overhand grip that interfered with wielding the hammer, whereas adults and older children ("adaptive planners") used an adaptive underhand grip. Adaptive and nonadaptive children differed in when and where they directed their gaze to obtain visual information, neural activation of the motor system before reaching, and straightness of their reach trajectories. Nonadaptive children immediately used a habitual overhand grip before gathering visual information, leaving insufficient time to form a plan before acting. Our novel bottom-up approach transcends mere speculation by providing converging evidence that the development of action planning depends on a real-time "tug of war" between habits and information gathering and processing.

Children's planning of efficient tool use in a social context

Efficient joint action requires that we anticipate situational demands both regarding our own and another person's perspective, and adapt our actions accordingly. Accordingly, when handing over a tool somebody else, it is advantageous to anticipate our future hand orientation (motor imagery), as well as the future orientation of the tool (mental rotation) relative to the other person, in order to make the transfer as smooth and efficient as possible. Furthermore, familiarity with specific tools might facilitate planning. We tested thirty-two 5.5- to 7-year-old children on a tool transfer task, asking if they consider another person's comfort when handing over different tools, and whether tool familiarity, motor imagery, and mental rotation are related to their grip choices. We compared the children's performance to that of an adult control group. Besides a rather low performance on the transfer task, we found differences in children's consideration of another person's comfort related to the specific tools they interacted with. Specifically, the unfamiliar tool (a bar) was transferred more efficiently than the familiar tools (hammer/brush). In addition, the results suggest a relation between children's consideration of another person's comfort and their mental rotation score, but no relation with their motor imagery score.

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.

Mental rotation performance in young adults with and without developmental coordination disorder

While there have been consistent behavioural reports of atypical hand rotation task (HRT) performance in adults with developmental coordination disorder (DCD), this study aimed to clarify whether this deficit could be attributed to specific difficulties in motor imagery (MI), as opposed to broad deficits in general mental rotation. Participants were 57 young adults aged 18-30 years with (n = 22) and without DCD (n = 35). Participants were compared on the HRT, a measure of MI, and the letter number rotation task (LNRT), a common visual imagery task. Only participants whose behavioural performance on the HRT suggested use of a MI strategy were included in group comparisons. Young adults with DCD were significantly less efficient compared to controls when completing the HRT yet showed comparable performance on the LNRT relative to adults with typical motor ability. Our data are consistent with the view that atypical HRT performance in adults with DCD is likely to be attributed to specific difficulties engaging in MI, as opposed to deficits in general mental rotation. Based on the theory that MI provides insight into the integrity of internal action representations, these findings offer further support for the internal modelling deficit hypothesis of DCD.

Eliciting End-State Comfort Planning in Children With and Without Developmental Coordination Disorder Using a Hammer Task: A Pilot Study

The end-state comfort (ESC) effect refers to the consistent tendency of healthy adults to end their movements in a comfortable end posture. In children with and without developmental coordination disorder (DCD), the results of studies focusing on ESC planning have been inconclusive, which is likely to be due to differences in task constraints. The present pilot study focused on the question whether children with and without DCD were able to change their planning strategy and were more likely to plan for ESC when demanded by complex object manipulations at the end of a task. To this end, we examined ESC planning in 18 children with and without DCD (aged 5–11years) using the previously used sword-task and the newly developed hammer-task. In the sword-task, children had to insert a sword in a wooden block, which could be relatively easily completed with an uncomfortable end-posture. In the hammer-task, children had to strike down a nail in a wooden pounding bench, which required additional force and speed demands, making it relatively difficult to complete the movement with an uncomfortable end-posture. In line with our hypothesis, the results demonstrated that children with and without DCD were more likely to plan for ESC on the hammer-task compared with the sword-task. Thus, while children with and without DCD show inconsistent ESC planning on many previously used tasks, the present pilot study shows that many of them are able to take into account the end-state of their movements if demanded by task constraints.

Preferential Reaching and End-State Comfort: How Task Demands Influence Motor Planning

Various factors (e.g., hand preference, object properties) constrain reach-to-grasp in hemispace. With object use, end-state comfort (ESC) has been shown to supersede the preferential use of one hand at the midline. To assess how location, size, and orientation of objects (dowel, mallet, cup) influence preferred-hand use and ESC (N = 50; M_age = 20.83), three preferential reaching tasks were implemented. Object location influenced hand selection in all tasks, along with size (cups) and orientation (mallets). Object location and orientation influenced ESC, but only with dowels and mallets. When oriented away from the preferred hand in hemispace, there was a higher occurrence of non-preferred hand use to facilitate ESC. Overall, findings add to understanding of ESC and preferential reaching with varying task demands.

Effects of virtual reality training intervention on predictive motor control of children with DCD - A randomized controlled trial

It has been hypothesised that deficits in the functions of predictive motor control and internal modeling may contribute to motor control issues of children with Developmental Coordination Disorder (DCD). Virtual reality (VR) technologies have great potential to provide opportunity for Motor observation and motor imagery (MI) which could enhance learning and development of motor skills in children with DCD. Thus, the present study aimed to investigate the benefits of a VR training intervention to improve predictive motor control functions of children with DCD. Forty female children with DCD (aged 7-10) were randomly assigned to VR and control groups. In this study, an experimental pre-post and follow-up design was used, and Predictive motor control functions were measured before and after the VR intervention and two-months later. Predictive motor control was evaluated using MI (by hand rotation task), action planning (by sword placement task), and rapid and online control (by rotational tracking task) tests. VR intervention consisted of a selection of Xbox 360 Kinect games that were performed for sixteen 30-min sessions over 8 weeks. Compared to the control group, the VR group improved significantly on measures of MI, motor planning, and rapid and online control scores from pre- to post-test and retained their performance to follow-up. Overall, it seems that virtual reality training program may be used as an appropriate intervention approach for developing the ability of MI and predictive motor control functions in DCD children.

Motor imagery in children with unilateral cerebral palsy: a case-control study

AIM

To evaluate whether children with cerebral palsy (CP) are able to engage in a motor imagery task. Possible associations between motor imagery and functional performance, working memory, age, and intelligence were also investigated.

METHOD

This is a case-control study that assessed 57 children (25 females, 32 males) with unilateral CP, aged 6 to 14 years (mean age: 10y 4mo; SD 2y 8mo) and 175 typically developing (control) children, aged 6 to 13 years (87 females, 88 males; mean age: 9y 4mo; SD 1y 11mo). The hand laterality judgment task was used to measure motor imagery ability. Reaction time, accuracy, and the effect of the biomechanical constraints were assessed in this task.

RESULTS

Performance in both groups followed the biomechanical constraints of the task, that is, longer reaction times to recognize stimuli rotated laterally when compared to medial stimuli. Reaction time means did not differ significantly between groups (p>0.05). Significant differences between the unilateral CP and control groups were observed for accuracy (p<0.05). Functional performance and working memory were correlates of motor imagery tasks.

INTERPRETATION

Results suggest that children with unilateral CP can engage in motor imagery; however, they commit more errors than typically developing controls. In addition, their performance in tasks of motor imagery is influenced by functional performance and working memory.

Motor Imagery Development in Children: Changes in Speed and Accuracy With Increasing Age

Although motor imagery has been pointed as a promising strategy for the rehabilitation of children with neurological disorders, information on their development throughout childhood and adolescence is still scarce. For instance, it is still unclear at what age they reach a development comparable to the motor imagery performance observed in adults. Herein we used a mental rotation task to assess motor imagery in 164 typically developing children and adolescents, which were divided into four age groups (6-7, 8-9, 10-11, and 12-13 years) and 30 adults. The effects of biomechanical constraints, accuracy, and reaction time of the mental rotation task were considered. ANOVA showed that all groups had the effect of biomechanical restrictions of the mental rotation task. We found a group effect for accuracy [F (4, 180) = 17,560; p < 0.00; η2 = 3.79] and reaction time [F (4, 180) = 17.5; p < 0.001, η2 = 0.615], with the results of children groups 6-7 and 8-9 years being significantly lower than the other groups (p < 0.05). In all the analyses, there were no differences regarding accuracy and reaction time among the participants of the age groups 10-11 and 12-13 years and adults (p > 0.05). Concluding, children aged 6-7 years were able to perform motor imagery, motor imagery ability improved as the participants' ages increased, and children aged 10 and over-performed similarly to adults.

The development of body representations in school-aged children

Following the triadic taxonomy, three different body representations do exist, namely the body semantics, the body structural representation and the body schema. The development of these body representations has been widely investigated in toddlers, but several issues remain to be addressed in school age. To assess age- and gender-related changes in different body representations and to investigate the presence of different patterns of interplay between these representations of the body, 90 children (age range: 7-10) and 37 young adults (age range: 18-35) were given tasks assessing the body semantics, the body structural representation and the body schema as well as control tasks. The present results suggested that the body schema, evaluated by means of hand laterality judgments, was still not completely developed in school-aged children, whereas the body structural representation reached an adult-like pattern by the age of 9-10 years. Finally, body semantics was fully developed in school-aged children. These findings were discussed in terms of their theoretical implications, for a better understanding of body representation development; also, implications for clinical assessment of body representation disorders were discussed.

Motor planning with and without motor imagery in children with Developmental Coordination Disorder

Children with Developmental Coordination Disorder (DCD) demonstrate inefficient motor planning ability with a tendency to opt for non-optimal planning strategies. Motor imagery can provide an insight to this planning inefficiency, as it may be a strategy for improving motor planning and thereby motor performance for those with DCD. In this study, we investigated the prevalence of end-state-comfort (ESC) and the minimal rotation strategy using a grip selection task in children with DCD with and without motor imagery instructions. Boys with (n = 14) and without DCD (n = 18) aged 7-12 years completed one, two and three colour sequences of a grip selection (octagon) task. Two conditions were examined; a Motor Planning (MP) condition requiring only the performance of the task and a Motor Imagery and Planning (MIP) condition, which included an instruction to imagine performing the movement before execution. For the MP condition, children with DCD ended fewer trials in ESC for the one (p = 0.001) and two colour (p = 0.002) sequences and used a minimal rotation strategy more often than those without DCD. For the MIP condition, the DCD group significantly increased their use of the ESC strategy for the one colour sequences (p = 0.014) while those without DCD improved for the two colour (p = 0.008) sequences. ESC level of the DCD group on the MIP condition was similar to those without DCD at baseline for all colour sequences. Motor imagery shows potential as a strategy for improving motor planning in children with DCD. Implications and limitations are discussed.

Emergence of anticipatory actions in a novel task

Humans normally adapt earlier segments of multistep motor actions in such a way that the execution of later segments is facilitated. For example, the kinematics of grasping movements are adapted to the requirements of the intended subsequent object manipulations. Here we studied which factors foster adaptation of earlier action segments to later ones in a novel task for which no prior experience existed. Participants executed a two-step isometric force production task, in which the force produced in the first segment determined the difficulty of the second segment. Adaptation of the first segment to the second one benefited from explicit knowledge of the dependency between both segments but not from extensive prior experience with the second segment. These observations show that adaptation of motor actions to subsequent actions demands the construction of a task representation that allows to plan the first action segment with respect to its successor. How specifically the first segment is tailored to the second one does not depend on prior experience with the second segment but depends on experience from performing the interdependent two-step action sequence.

Mirror neuron system activation in children with developmental coordination disorder: A replication functional MRI study

BACKGROUND

It has been hypothesised that abnormal functioning of the mirror neuron system (MNS) may lead to deficits in imitation and the internal representation of movement, potentially contributing to the motor impairments associated with developmental coordination disorder (DCD).

AIMS

Using fMRI, this study examined brain activation patterns in children with and without DCD on a finger adduction/abduction task during four MNS activation states: observation; motor imagery; execution; and imitation.

METHODS AND PROCEDURES

Nineteen boys (8.25-12.75 years) participated, including 10 children with DCD (≤16th percentile on MABC-2; no ADHD/ASD), and nine typically developing controls (≥25th percentile on MABC-2).

OUTCOMES AND RESULTS

Even though children with DCD displayed deficits behaviourally on imitation (Sensory Integration & Praxis Test Subtests) and motor imagery assessments prior to scanning, no differences in MNS activation were seen between the DCD and control groups at a neurological level, with both groups activating mirror regions effectively across conditions. Small clusters of decreased activation during imitation were identified in non-mirror regions in the DCD group, including the thalamus, caudate, and posterior cingulate - regions involved in motor planning and attentional processes.

CONCLUSIONS AND IMPLICATIONS

The results of this study do not provide support for the MNS dysfunction theory as a possible causal mechanism for DCD. Further research to explore attentional and motor planning processes and how they may interact at a network level may enhance our understanding of this complex disorder.

Investigating motor planning in children with DCD: Evidence from simple and complex grip-selection tasks

Several studies suggest that children with Developmental Coordination Disorder (DCD) may be able to plan simple movements as well as their peers, but experience increasing difficulties as the movements become complex. The present study aimed to clarify the nature of motor planning in DCD, including a putative deficit, by being the first to investigate motor planning using converging measures of simple and complex motor planning in a single sample of children with DCD. Boys aged between 8 and 12 years with (n = 10) and without DCD (n = 17) completed three commonly used 'simple' (bar grasping, sword, and bar transport tasks) measures and one 'complex' (octagon task) measure of end-state-comfort (ESC), a classic measurement of motor planning ability. To achieve ESC when manipulating an object, a person may choose to start with an uncomfortable grip in order to end the movement in a comfortable position. Results indicate that the participants with DCD planned for ESC as efficiently as their peers when performing the 'simple' measures of ESC but were significantly less likely to end their performances in ESC than those without DCD for the more 'complex' octagon task. Taken together, our data suggest that school-aged children with DCD may be able to plan simple movements as efficiently as their peers, but have more difficulty doing so for multi-movement or complex sequences. Based on the assumption that the efficiency of such motor planning is dependent on the integrity of internal modelling systems, we argue that our study provides indirect support for the internal modelling deficit hypothesis.

Feedforward motor control in developmental dyslexia and developmental coordination disorder: Does comorbidity matter?

BACKGROUND AND AIM

Feedforward and online controls are two facets of predictive motor control from internal models, which is suspected to be impaired in learning disorders. We examined whether the feedforward component is affected in children (8-12 years) with developmental dyslexia (DD) and/or with developmental coordination disorder (DCD) compared to typically developing (TD) children.

METHODS

Children underwent a bimanual unloading paradigm during which a load supported to one arm, the postural arm, was either unexpectedly unloaded by a computer or voluntary unloaded by the subject with the other arm.

RESULTS

All children showed a better stabilization (lower flexion) of the postural arm and an earlier inhibition of the arm flexors during voluntary unloading, indicating anticipation of unloading. Between-group comparisons of kinematics and electromyographic activity of the postural arm revealed that the difference during voluntary unloading was between DD-DCD children and the other groups, with the former showing a delayed inhibition of the flexor muscles.

CONCLUSION

Deficit of the feedforward component of motor control may particularly apply to comorbid subtypes, here the DD-DCD subtype. The development of a comprehensive framework for motor performance deficits in children with learning disorders will be achieved only by dissociating key components of motor prediction and focusing on subtypes and comorbidities.

Corticospinal excitability during motor imagery is reduced in young adults with developmental coordination disorder

While a compelling body of behavioral research suggests that individuals with developmental coordination disorder (DCD) experience difficulties engaging motor imagery (MI), very little is known about the neural correlates of this deficit. Since corticospinal excitability is a predictor of MI proficiency in healthy adults, we reasoned that decreased MI efficiency in DCD may be paralleled by atypical primary motor cortex (PMC) activity. Participants were 29 young adults aged 18- 36 years: 8 with DCD (DCD) and 21 controls. Six participants with DCD and 15 controls showed behavioral profiles consistent with the use of a MI strategy (MI users) while performing a novel adaptation of the classic hand laterality task (HLT). Single-pulse transcranial magnetic stimulation (TMS) was administered to the hand node of the left PMC (hPMC) at 50ms, 400ms or 650ms post stimulus presentation during the HLT. Motor-evoked potentials (MEPs) were recorded from the right first dorsal interosseous (FDI) via electromyography. As predicted, MI users with DCD were significantly less efficient than MI using controls, shown by poorer performance on the HLT. Importantly, unlike healthy controls, no evidence of enhanced hPMC activity during MI was detected in our DCD group. Our data are consistent with the view that inefficient MI in DCD may be subserved by decreased hPMC activity. These findings are an important step towards clarifying the neuro-cognitive correlates of poor MI ability and motor skill in individuals with DCD.

Preschool children adapt grasping movements to upcoming object manipulations: Evidence from a dial rotation task

In adults, the motor plans for object-directed grasping movements reflects the anticipated requirements of intended future object manipulations. This prospective mode of planning has been termed second-order planning. Surprisingly, second-order planning is thought to be fully developed only by 10 years of age, when children master seemingly more complex motor skills. In this study, we tested the hypothesis that already 5- and 6-year-old children consistently use second-order planning but that this ability does not become apparent in tasks that are traditionally used to probe it. We asked 5- and 6-year-olds and adults to grasp and rotate a circular dial in a clockwise or counterclockwise direction. Although children's grasp selections were less consistent on an intra- and inter-individual level than adults' grasp selections, all children adjusted their grasps to the upcoming dial rotations. By contrast, in an also administered bar rotation task, only a subset of children adjusted their grasps to different bar rotations, thereby replicating previous results. The results indicate that 5- and 6-year-olds consistently use second-order planning in a dial rotation task, although this ability does not become apparent in bar rotation tasks.

Primary Motor Cortex Excitability Is Modulated During the Mental Simulation of Hand Movement

OBJECTIVES

It is unclear whether the primary motor cortex (PMC) is involved in the mental simulation of movement [i.e., motor imagery (MI)]. The present study aimed to clarify PMC involvement using a highly novel adaptation of the hand laterality task (HLT).

METHODS

Participants were administered single-pulse transcranial magnetic stimulation (TMS) to the hand area of the left PMC (hPMC) at either 50 ms, 400 ms, or 650 ms post stimulus presentation. Motor-evoked potentials (MEPs) were recorded from the right first dorsal interosseous via electromyography. To avoid the confound of gross motor response, participant response (indicating left or right hand) was recorded via eye tracking. Participants were 22 healthy adults (18 to 36 years), 16 whose behavioral profile on the HLT was consistent with the use of a MI strategy (MI users).

RESULTS

hPMC excitability increased significantly during HLT performance for MI users, evidenced by significantly larger right hand MEPs following single-pulse TMS 50 ms, 400 ms, and 650 ms post stimulus presentation relative to baseline. Subsequent analysis showed that hPMC excitability was greater for more complex simulated hand movements, where hand MEPs at 50 ms were larger for biomechanically awkward movements (i.e., hands requiring lateral rotation) compared to simpler movements (i.e., hands requiring medial rotation).

CONCLUSIONS

These findings provide support for the modulation of PMC excitability during the HLT attributable to MI, and may indicate a role for the PMC during MI. (JINS, 2017, 23, 185-193).