Although the neural bases of the brain associated with movement disorders in children with developmental coordination disorder (DCD) are becoming clearer, the information is not sufficient because of the lack of extensive brain function research. Therefore, it is controversial about effective intervention methods focusing on brain function. One of the rehabilitation techniques for movement disorders involves intervention using motor imagery (MI). MI is often used for movement disorders, but most studies involve adults and healthy children, and the MI method for children with DCD has not been studied in detail. Therefore, a review was conducted to clarify the neuroscientific basis of the methodology of intervention using MI for children with DCD. The neuroimaging review included 20 magnetic resonance imaging studies, and the neurorehabilitation review included four MI intervention studies. In addition to previously reported neural bases, our results indicate decreased activity of the bilateral thalamus, decreased connectivity of the sensory-motor cortex and the left posterior middle temporal gyrus, bilateral posterior cingulate cortex, precuneus, cerebellum, and basal ganglia, loss of connectivity superiority in the abovementioned areas. Furthermore, reduction of gray matter volume in the right superior frontal gyrus and middle frontal gyrus, lower fractional anisotropy, and axial diffusivity in regions of white matter pathways were found in DCD. As a result of the review, children with DCD had less activation of the left brain, especially those with mirror neurons system (MNS) and sensory integration functions. On the contrary, the area important for the visual space processing of the right brain was activated. Regarding of characteristic of the MI methods was that children observed a video related to motor skills before the intervention. Also, they performed visual-motor tasks before MI training sessions. Adding action observation during MI activates the MNS, and performing visual-motor tasks activates the basal ganglia. These methods may improve the deactivated brain regions of children with DCD and may be useful as conditioning before starting training. Furthermore, we propose a process for sharing the contents of MI with the therapist in language and determining exercise strategies.

Objective: To investigate whether the changes in the corticospinal excitability contribute to the anticipatory postural adjustments (APAs) in the lower limb muscles when performing the ballistic upper limb movement of the dart throwing.Methods: We examined the primary motor cortex (M1) excitability of the lower limb muscles [tibialis anterior (TA) and soleus (SOL) muscles] during the APA phase by using transcranial magnetic stimulation (TMS) in the healthy volunteers. The surface electromyography (EMG) of anterior deltoid, triceps brachii, biceps brachii, TA, and SOL muscles was recorded and the motor evoked potential (MEP) to TMS was recorded in the TA muscle along with the SOL muscle. TMS at the hotspot of the TA muscle was applied at the timings immediately prior to the TA onset. The kinematic parameters including the three-dimensional motion analysis and center of pressure (COP) during the dart throwing were also assessed.Results: The changes in COP and EMG of the TA muscle occurred preceding the dart throwing, which involved a slight elbow flexion followed by an extension. The correlation analysis revealed that the onset of the TA muscle was related to the COP change and the elbow joint flexion. The MEP amplitude in the TA muscle, but not that in the SOL muscle, significantly increased immediately prior to the EMG burst (100, 50, and 0 ms prior to the TA onset).Conclusion: Our findings demonstrate that the corticospinal excitability of the TA muscle increases prior to the ballistic upper limb movement of the dart throwing, suggesting that the corticospinal pathway contributes to the APA in the lower limb in a muscle-specific manner.

Whether attentional focus modulates the corticospinal excitability of the lower limb muscles in anticipatory postural adjustments (APAs) when performing a ballistic movement of the upper limb remains unclear. The present study used transcranial magnetic stimulation (TMS) to examine the corticospinal excitability of the lower limb muscles along with the kinematic profiles during dart throwing with different attentional foci, external focus (EF) and internal focus (IF). In 13 healthy participants, TMS was applied immediately before electromyographic onset of the tibialis anterior (TA) muscle, and the motor evoked potential (MEP) was recorded in the TA and soleus (SOL) muscles. The performance accuracy was significantly higher in the EF condition than in the IF condition. In both EF and IF conditions, MEP amplitude in the TA muscle, but not the SOL muscle, was significantly higher immediately before TA muscle onset (− 100, − 50, and 0 ms) compared to the control. In particular, the MEP increment in the TA muscle before TA muscle onset (− 50 and 0 ms) was significantly larger in the EF condition than in the IF condition. Our findings provide the first evidence for the modulation of corticospinal excitability in APA by changing attentional focus.

Although it is known that motor performance improves through motor skill learning, it is unclear whether the success rate representation affects the motor performance in association with the corticospinal excitability changes through the learning process. By using transcranial magnetic stimulation (TMS), we examined the changes in the corticospinal excitability of the engaged muscles (first dorsal interosseous, extensor and flexor carpi radialis, and anterior deltoid, FDI, ECR, FCR, AD muscles) before and after a short‐term learning of a dynamic and coordinated upper limb movement. The TMS coil was placed on the motor hots pot of the FDI muscle. Nineteen healthy volunteers using their dominant hand were asked to hold a pen and dot (black ink) the center of an A4‐size paper at which a small red ink dot was printed. The subjects performed the trials at 1 Hz, and were asked to put their hand higher than 100 mm apart from the paper surface trial‐by‐trial. All subjects were divided into two groups; one engaged motor learning without success rate (SR) representation (control group) and other with (SR group). With the control group, 50 trials per session, totally 20 sessions were performed in the motor learning sessions by using the same papers. With the SR group, on the other hand, the performance before learning (50 trials) was assessed before the experiment on a separate day, and a circle with a diameter of which the length was calculated by the success rate of 60 percents according to the performance before learning (50 points distance from the target), was printed around the target red dot in the motor learning sessions. The changes in the performance, electromyography (EMG), and motor evoked potentials (MEP) to TMS before and after motor learning were analyzed. The results showed that the error from the target significantly decreased through the learning in both groups, and the success rate was significantly smaller in the SR group compared with that in the control group. The EMG activity of FDI muscle was smaller, and that of AD muscle was larger in the SR group than those in the control group, while difference in the EMGs showed nether in the ECR nor FCR muscle. Through learning, interestingly, MEP in the FDI muscle was significantly larger in the SR group than that in the control group at resting state, but no difference in the MEP between the groups during voluntary movements (motor task). Also, the MEP/Background EMG ratio showed no difference between the groups. Our results suggest that, in the motor learning the performance can be further improved by representing the success rate of the motor task, and that the central motor command emphasizing on the proximal rather than distal muscle may contribute to the improved performance.

Attentional focus can affect motor performance and learning. It is known that external focus (EF) which concentrated on the movement outcome leads better performance and efficient motor output rather than internal focus (IF) which concentrated on one's body movement. It remains unclear whether the attentional focus modulates the corticospinal excitability during anticipatory postural adjustments (APA). In the present study, we using transcranial magnetic stimulation (TMS) examined the excitability changes in the primary motor cortex (M1) during dart throwing with different attentional focuses. We hypothesized that the APA duration and magnitude is different between EF and IF conditions, and the corticospinal excitability of lower leg muscle increases in the phase of APA, while the extent to which modulation is different between conditions. Fifteen healthy volunteers were asked to perform dart throwing with the dominant hand with a visual cue under the EF condition (focus on the flight trajectory of the dart) and IF condition (focus on the elbow angle of the dominant hand). The participants performing the tasks stood on a force plate with the legs closed, and we measured the displacement of center of pressure (COP). Electromyography (EMG) was recorded from the anterior deltoid, triceps brachii (TB), tibialis anterior (TA), and soleus muscles. Because the EMG of TA muscle was clearly observed from about 300 ms before the EMG onset of TB muscle (agonist muscle of throwing), TMS was applied over the hotspot of TA muscle in the contralateral M1 at the timings of the visual cue, 0 to 100 ms prior to the EMG onset of TA muscle, and the EMG onset of TB muscle. The distance from the bulls‐eye was significantly shorter with EF than that with IF. Neither the difference in the total length of COP and rectangle area nor in the APA duration and magnitude was observed between EF and IF conditions. The motor evoked potential (MEP) amplitude in the TA muscle at ‐100ms, ‐50 ms, TA onset, and TB onset significantly increased in comparison with that at control in both conditions. In particular, MEP at ‐50 ms, TA onset, and TB onset were significantly larger with EF than those with IF, whereas there were no significant differences in MEP at visual cue and ‐100 ms between EF and IF conditions. Our results demonstrate that the excitability of corticospinal projections to the lower leg muscle increases immediately prior to a ballistic movement of the upper limb. It suggests that, by changing the attentional focus the cortical contribution to the postural control is modulated which may improve motor performance and efficacy of the movement execution.