Exploring Methodological Issues in Mental Practice for Upper-Extremity Function Following Stroke-Related Paralysis: A Scoping Review.

In this scoping review, we aimed to comprehensively clarify the methodology of Mental practice (MP) by systematically mapping studies documenting the application of MP to post-stroke paralytic upper-extremity function. Specifically, when is an MP intervention most commonly applied after stroke onset? What is the corresponding MP load (intervention time, number of intervention days, and intervention period)? What are the most common methods of Motor Imagery (MI) recall and MI tasks used during the application of MP? Is MP often used in conjunction with individual rehabilitation? What are the paralyzed side's upper-limb and cognitive function levels at the start of an MP intervention? The research questions were identified according to PRISMA-ScR. The PubMed, Scopus, Medline, and Cochrane Library databases were used to screen articles published until 19 July 2022. In total, 694 English-language articles were identified, of which 61 were finally included. Most of the studies were conducted in the chronic phase after stroke onset, with limited interventions in the acute or subacute phase. The most common intervention time was ≤30 min and intervention frequency was 5 times/week in MP. An audio guide was most commonly used to recall MI during MP, and 50 studies examined the effects of MP in combination with individual rehabilitation. The Fugl-Meyer Assessment mean for the 38 studies, determined using the Fugl-Meyer Assessment, was 30.3 ± 11.5. Additional research with the aim of unifying the widely varying MP methodologies identified herein is warranted.

Differences in Cortical Area Activity and Motor Imagery Vivid-Ness during Evaluation of Motor Imagery Tasks in Right and Left Hemiplegics.

The ability to develop vivid motor imagery (MI) is important for effective mental practice. Therefore, we aimed to determine differences in the MI clarity and cortical area activity between patients with right hemiplegia and left hemiplegia after stroke in an MI task. In total, 11 participants with right hemiplegia and 14 with left hemiplegia were categorized into two groups. The MI task required the flexion and extension of the finger on the paralyzed side. Considering that MI vividness changes with MI practice, we measured the MI vividness and cortical area activity during the task before and after MI practice. MI vividness was evaluated subjectively using the visual analog scale, and cerebral hemodynamics during the task were measured using near-infrared spectroscopy in cortical regions during the MI task. The MI sharpness and cortical area activity in the MI task were significantly lower in the right hemiplegia group than in the left hemiplegia group. Therefore, when practicing mental practices with right hemiplegia, it is necessary to devise ways by which to increase MI vividness.

Continuous Repetition Motor Imagery Training and Physical Practice Training Exert the Growth of Fatigue and Its Effect on Performance.

Continuous repetition of motor imagery leads to mental fatigue. This study aimed to examine whether fatigue caused by motor imagery training affects improvement in performance and the change in corticospinal excitability. The participants were divided into "physical practice training" and "motor imagery training" groups, and a visuomotor task (set at 50% of maximal voluntary contraction in participants) was performed to assess the training effect on fatigue. The measurements were recorded before and after training. Corticospinal excitability at rest was measured by transcranial magnetic stimulation according to the Neurophysiological Index. Subjective mental fatigue and muscle fatigue were assessed by using the visual analog scale and by measuring the pinch force, respectively. Additionally, the error area was evaluated and calculated at pre-, mid-, and post-terms after training, using a visuomotor task. After training, muscle fatigue, subjective mental fatigue, and decreased corticospinal excitability were noted in both of the groups. Moreover, the visuomotor task decreased the error area by training; however, there was no difference in the error area between the mid- and post-terms. In conclusion, motor imagery training resulted in central fatigue by continuous repetition, which influenced the improvement in performance in the same manner as physical practice training.

A Method for Using Video Presentation to Increase Cortical Region Activity during Motor Imagery Tasks in Stroke Patients.

Previous studies have reported that stroke patients have difficulty recalling the motor imagery (MI) of a task, also known as MI vividness. Research on combining MI with action observation is gaining importance as a method to improve MI vividness. We enrolled 10 right-handed stroke patients and compared MI vividness and cortical activity under different presentation methods (no inverted image, inverted image of another individual's hand, and an inverted image of the patient's nonparalyzed hand) using near-infrared spectroscopy. Images of the nonparalyzed upper limb were inverted to make the paralyzed upper limb appear as if it were moving. Three tasks (non inverted image, AO + MI (other hand), AO + MI (own hand)) were randomly performed on 10 stroke patients. MI vividness was significantly higher when the inverted image of the nonparalyzed upper limb was presented compared to the other conditions (p < 0.01). The activity of the cortical regions was also significantly enhanced (p < 0.01). Our study highlights the potential application of inverted images of a stroke patient's own nonparalyzed hand in mental practice to promote the motor recovery of stroke patients. This technique achieved higher levels of MI vividness and cortical activity when performing motor tasks.

A method for using video presentation to increase the vividness and activity of cortical regions during motor imagery tasks.

In recent years, mental practice (MP) using laterally inverted video of a subject's non-paralyzed upper limb to improve the vividness of presented motor imagery (MI) has been shown to be effective for improving the function of a paralyzed upper limb. However, no studies have yet assessed the activity of cortical regions engaged during MI task performance using inverse video presentations and neurophysiological indicators. This study sought to investigate changes in MI vividness and hemodynamic changes in the cerebral cortex during MI performance under the following three conditions in near-infrared spectroscopy: MI-only without inverse video presentation (MI-only), MI with action observation (AO) of an inverse video presentation of another person's hand (AO + MI (other hand)), and MI with AO of an inverse video presentation of a participant's own hand (AO + MI (own hand)). Participants included 66 healthy right-handed adults (41 men and 25 women; mean age: 26.3 ± 4.3 years). There were 23 patients in the MI-only group (mean age: 26.4 ± 4.1 years), 20 in the AO + MI (other hand) group (mean age: 25.9 ± 5.0 years), and 23 in the AO + MI (own hand) group (mean age: 26.9 ± 4.1 years). The MI task involved transferring 1 cm × 1 cm blocks from one plate to another, once per second, using chopsticks held in the non-dominant hand. Based on a visual analog scale (VAS), MI vividness was significantly higher in the AO + MI (own hand) group than in the MI-only group and the AO + MI (other hand) group. A main effect of condition was revealed in terms of MI vividness, as well as regions of interest (ROIs) in certain brain areas associated with motor processing. The data suggest that inverse video presentation of a person's own hand enhances the MI vividness and increases the activity of motor-related cortical areas during MI. This study was approved by the Institutional Ethics Committee of Nagasaki University Graduate School of Biomedical and Health Sciences (approval No. 18121303) on January 18, 2019.

A Study on the Effect of Mental Practice Using Motor Evoked Potential-Based Neurofeedback.

This study aimed to investigate whether the effect of mental practice (motor imagery training) can be enhanced by providing neurofeedback based on transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEP). Twenty-four healthy, right-handed subjects were enrolled in this study. The subjects were randomly allocated into two groups: a group that was given correct TMS feedback (Real-FB group) and a group that was given randomized false TMS feedback (Sham-FB group). The subjects imagined pushing the switch with just timing, when the target circle overlapped a cross at the center of the computer monitor. In the Real-FB group, feedback was provided to the subjects based on the MEP amplitude measured in the trial immediately preceding motor imagery. In contrast, the subjects of the Sham-FB group were provided with a feedback value that was independent of the MEP amplitude. TMS was applied when the target, moving from right to left, overlapped the cross at the center of the screen, and the MEP amplitude was measured. The MEP was recorded in the right first dorsal interosseous muscle. We evaluated the pre-mental practice and post-mental practice motor performance in both groups. As a result, a significant difference was observed in the percentage change of error values between the Real-FB group and the Sham-FB group. Furthermore, the MEP was significantly different between the groups in the 4th and 5th sets. Therefore, it was suggested that TMS-induced MEP-based neurofeedback might enhance the effect of mental practice.

Corticospinal excitability during motor imagery is diminished by continuous repetition-induced fatigue.

Application of continuous repetition of motor imagery can improve the performance of exercise tasks. However, there is a lack of more detailed neurophysiological evidence to support the formulation of clear standards for interventions using motor imagery. Moreover, identification of motor imagery intervention time is necessary because it exhibits possible central fatigue. Therefore, the purpose of this study was to elucidate the development of fatigue during continuous repetition of motor imagery through objective and subjective evaluation. The study involved two experiments. In experiment 1, 14 healthy young volunteers were required to imagine grasping and lifting a 1.5-L plastic bottle using the whole hand. Each participant performed the motor imagery task 100 times under each condition with 48 hours interval between two conditions: 500 mL or 1500 mL of water in the bottle during the demonstration phase. Mental fatigue and a decrease in pinch power appeared under the 1500-mL condition. There were changes in concentration ability or corticospinal excitability, as assessed by motor evoked potentials, between each set with continuous repetition of motor imagery also under the 1500-mL condition. Therefore, in experiment 2, 12 healthy volunteers were required to perform the motor imagery task 200 times under the 1500-mL condition. Both concentration ability and corticospinal excitability decreased. This is the first study to show that continuous repetition of motor imagery can decrease corticospinal excitability in addition to producing mental fatigue. This study was approved by the Institutional Ethics Committee at the Nagasaki University Graduate School of Biomedical and Health Sciences (approval No. 18121302) on January 30, 2019.

Comparison of cerebral activation between motor execution and motor imagery of self-feeding activity.

Motor imagery is defined as an act wherein an individual contemplates a mental action of motor execution without apparent action. Mental practice executed by repetitive motor imagery can improve motor performance without simultaneous sensory input or overt output. We aimed to investigate cerebral hemodynamics during motor imagery and motor execution of a self-feeding activity using chopsticks. This study included 21 healthy right-handed volunteers. The self-feeding activity task comprised either motor imagery or motor execution of eating sliced cucumber pickles with chopsticks to examine eight regions of interest: pre-supplementary motor area, supplementary motor area, bilateral prefrontal cortex, premotor area, and sensorimotor cortex. The mean oxyhemoglobin levels were detected using near-infrared spectroscopy to reflect cerebral activation. The mean oxyhemoglobin levels during motor execution were significantly higher in the left sensorimotor cortex than in the supplementary motor area and the left premotor area. Moreover, significantly higher oxyhemoglobin levels were detected in the supplementary motor area and the left premotor area during motor imagery, compared to motor execution. Supplementary motor area and premotor area had important roles in the motor imagery of self-feeding activity. Moreover, the activation levels of the supplementary motor area and the premotor area during motor execution and motor imagery are likely affected by intentional cognitive processes. Levels of cerebral activation differed in some areas during motor execution and motor imagery of a self-feeding activity. This study was approved by the Ethical Review Committee of Nagasaki University (approval No. 18110801) on December 10, 2018.

Effects of prism adaptation on auditory spatial attention in patients with left unilateral spatial neglect: a non-randomized pilot trial.

A short period of adaptation to a prismatic shift of the visual field to the right briefly but significantly improves left unilateral spatial neglect. Additionally, prism adaptation affects multiple modalities, including processes of vision, auditory spatial attention, and sound localization. This non-randomized, single-center, controlled trial aimed to examine the immediate effects of prism adaptation on the sound-localization abilities of patients with left unilateral spatial neglect using a simple source localization test. Subjects were divided by self-allocation into a prism-adaptation group (n = 11) and a control group (n = 12). At baseline, patients with left unilateral spatial neglect showed a rightward deviation tendency in the left space. This tendency to right-sided bias in the left space was attenuated after prism adaptation. However, no changes were observed in the right space of patients with left unilateral spatial neglect after prism adaptation, or in the control group. Our results suggest that prism adaptation improves not only vision and proprioception but also auditory attention in the left space of patients with left unilateral spatial neglect. Our findings demonstrate that a single session of prism adaptation can significantly improve sound localization in patients with left unilateral spatial neglect. However, in this study, it was not possible to accurately determine whether the mechanism was a chronic change in head orientation or a readjustment of the spatial representation of the brain; thus, further studies need to be considered.

Cerebral haemodynamics during motor imagery of self-feeding with chopsticks: differences between dominant and non-dominant hand.

Purpose: Motor imagery is defined as a dynamic state during which a subject mentally simulates a given action without overt movements. Our aim was to use near-infrared spectroscopy to investigate differences in cerebral haemodynamics during motor imagery of self-feeding with chopsticks using the dominant or non-dominant hand.Materials and methods: Twenty healthy right-handed people participated in this study. The motor imagery task involved eating sliced cucumber pickles using chopsticks with the dominant (right) or non-dominant (left) hand. Activation of regions of interest (pre-supplementary motor area, supplementary motor area, pre-motor area, pre-frontal cortex, and sensorimotor cortex was assessed.Results: Motor imagery vividness of the dominant hand tended to be significantly higher than that of the non-dominant hand. The time of peak oxygenated haemoglobin was significantly earlier in the right pre-frontal cortex than in the supplementary motor area and left pre-motor area. Haemodynamic correlations were detected in more regions of interest during dominant-hand motor imagery than during non-dominant-hand motor imagery.Conclusions: Haemodynamics might be affected by differences in motor imagery vividness caused by variations in motor manipulation.

Effect of electrical stimulation of antagonist muscles for voluntary motor drive.

Voluntary motor drive is an important central command that descends via the corticospinal tract to initiate muscle contraction. When electrical stimulation (ES) is applied to an antagonist or agonist muscle, it changes the agonist muscle's representative motor cortex and thus its voluntary motor drive. In this study, we used a reaction time task to compare the effects of weak and strong ES of the antagonist or agonist muscle during the premotor period of a wrist extension. We recorded motor evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS) that was applied to the extensor carpi radialis (ECR; agonist) and flexor carpi radialis (FCR; antagonist). When stronger ES intensities were applied to the antagonist, the MEP control ratio in the ECR significantly increased during the premotor time. Furthermore, the MEP control ratio with stronger antagonist ES intensity was significantly larger than that in the agonist for the same ES intensity. In the FCR, the MEP control ratio was also significantly greater at the strong ES intensity than at the weak ES intensity. Furthermore, the MEP control ratio in the antagonist with a strong ES intensity was significantly larger than that in the agonist with the same ES intensity. These results suggest that agonist corticomotor excitability might be enhanced by ES of the antagonist, which in turn strongly activates the descending motor system in the preparation of agonist contraction.

A retrospective evaluation of thalamic targeting for tremor deep brain stimulation using high-resolution anatomical imaging with supplementary fiber tractography.

OBJECTIVES: Deep brain stimulation (DBS) of the ventral intermediate (Vim) thalamic nucleus is used to treat tremors. Here, we identified the Vim nucleus on fast gray matter acquisition T1 inversion recovery (FGATIR) images and delineated the dentate-rubrothalamic tract (DRT) to determine the DBS target. We evaluated whether this method could consistently identify the Vim nucleus by anatomical imaging and fiber tractography. METHODS: We retrospectively reviewed clinical data of patients who underwent unilateral thalamic DBS for severe tremor disorders. We evaluated outcomes at baseline, 6 months and 1 year following intervention, and annually thereafter. We reviewed preoperative planning to determine whether our tractography technique could consistently depict the DRT, and evaluated implanted electrode position by fusing postoperative CT scans to preoperative MR images. RESULTS: Seven patients (three men and four women) were included; preoperative diagnoses included essential tremor (n = 3), Parkinson's (n = 2), and Holmes tremor (n = 2). All patients responded to DBS therapy; motor scores improved at 6-month and last follow-up. The Vim nucleus was successfully identified, as the DRT was depicted in all cases. Of ten active DBS contacts in seven leads, four contacts were located outside of the depicted DRT, and these contacts tended to require higher stimulation intensity. CONCLUSIONS: The Vim nucleus was successfully identified with FGATIR. Our methods may be useful to determine optimal DBS trajectory, and potentially improve outcomes.

Somatosensory cortex excitability changes due to differences in instruction conditions of motor imagery.

Purpose Vivid motor imagery appears to be associated with improved motor learning efficiency. However, the practical difficulties in measuring vivid motor imagery warrant new analytical approaches. The present study aimed to determine the instruction conditions for which vividness in motor imagery could be more easily seen and the excitability of the sensory cortex as it relates to the motor image. Materials and methods In total, 15 healthy, right-handed volunteers were instructed to imagine grasping a rubber ball under a verbal-only instruction condition (verbal condition), a verbal + visual instruction condition (visual condition), and a verbal + execution (physically grasping a real ball) condition (execution condition). We analyzed motor imagery-related changes in somatosensory cortical excitability by comparing somatosensory-evoked potentials in each condition with the rest (control) condition. We also used a visual analogue scale to measure subject-reported vividness of imagery. Results We found the N33 component was significantly lower in the execution condition than in the rest condition (p < 0.05). The results suggested a gating effect via central efferent mechanisms that affected the excitability of areas 3b or 1 in the primary somatosensory cortex, but only in the execution condition. Conclusions These data suggest that experiencing a movement through actual motor execution immediately prior to performing mental imagery of that movement enhances the excitability of motor-related cortical areas. It is suggested that the excitability of the motor-related region increased as a result of the motor imagery in the execution condition acting on the corresponding somatosensory cortex.

Effect of mental practice using inverse video of the unaffected upper limb in a subject with chronic hemiparesis after stroke.

[Purpose] The aim of this case study was to investigate whether a method of mental practice (MP) using an inverse video of a subject's unaffected limb to complement the vividness of motor imagery (MI) would be effective for improving affected upper limb function. [Subjects and Methods] The participant was 60-year-old male in the chronic stage of stroke recovery with left sided hemiparesis. The design of the study was AB method of Single-System-Design. He performed the MP as a home program with DVD. The intervention lasted 30 minutes a session, twice a day, 5 times a week, over 6 weeks. The DVD was created using inverse video of his unaffected upper limb. Primary outcome measures were used the Fugl-Meyer Assessment for upper limb (FMA) and the Motor Activity Log (MAL) 3 times each baseline, intervention and follow-up. The subjective vividness of MI was assessed by the Visual Analog Scale (VAS). [Results] FMA and MAL score during intervention was improved significantly comparing to baseline, and maintained in withdrawal. VAS score was improved in withdrawal comparing to baseline. [Conclusion] Results suggested that effect of mental practice for stroke patients increased by vividness of motor imagery was improved by the inverse video.

Effect of neuromuscular electrical stimulation on motor cortex excitability upon release of tonic muscle contraction.

The aim of the present study was to investigate the neurophysiological triggers underlying muscle relaxation from the contracted state, and to examine the mechanisms involved in this process and their subsequent modification by neuromuscular electrical stimulation (NMES). Single-pulse transcranial magnetic stimulation (TMS) was used to produce motor-evoked potentials (MEPs) and short-interval intracortical inhibition (SICI) in 23 healthy participants, wherein motor cortex excitability was examined at the onset of voluntary muscle relaxation following a period of voluntary tonic muscle contraction. In addition, the effects of afferent input on motor cortex excitability, as produced by NMES during muscle contraction, were examined. In particular, two NMES intensities were used for analysis: 1.2 times the sensory threshold and 1.2 times the motor threshold (MT). Participants were directed to execute constant wrist extensions and to release muscle contraction in response to an auditory "GO" signal. MEPs were recorded from the flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles, and TMS was applied at three different time intervals (30, 60, and 90 ms) after the "GO" signal. Motor cortex excitability was greater during voluntary ECR and FCR relaxation using high-intensity NMES, and relaxation time was decreased. Each parameter differed significantly between 30 and 60 ms. Moreover, in both muscles, SICI was larger in the presence than in the absence of NMES. Therefore, the present findings suggest that terminating a muscle contraction triggers transient neurophysiological mechanisms that facilitate the NMES-induced modulation of cortical motor excitability in the period prior to muscle relaxation. High-intensity NMES might facilitate motor cortical excitability as a function of increased inhibitory intracortical activity, and therefore serve as a transient trigger for the relaxation of prime mover muscles in a therapeutic context.

Monitoring Local Regional Hemodynamic Signal Changes during Motor Execution and Motor Imagery Using Near-Infrared Spectroscopy.

The aim of this study was to clarify the topographical localization of motor-related regional hemodynamic signal changes during motor execution (ME) and motor imagery (MI) by using near-infrared spectroscopy (NIRS), as this technique is more clinically expedient than established methods (e.g., fMRI). Twenty right-handed healthy subjects participated in this study. The experimental protocol was a blocked design consisting of 3 cycles of 20 s of task performance and 30 s of rest. The tapping sequence task was performed with their fingers under 4 conditions: ME and MI with the right or left hand. Hemodynamic brain activity was measured with NIRS to monitor changes in oxygenated hemoglobin (oxy-Hb) concentration. Oxy-Hb in the somatosensory motor cortex (SMC) increased significantly only during contralateral ME and showed a significant interaction between task and hand. There was a main effect of hand in the left SMC. Although there were no significant main effects or interactions in the supplemental motor area (SMA) and premotor area (PMA), oxy-Hb increased substantially under all conditions. These results clarified the topographical localization by motor-related regional hemodynamic signal changes during ME and MI by using NIRS.

Hemispheric asymmetry of ipsilateral motor cortex activation in motor skill learning.

In this study, we investigated how ipsilateral motor cortex (M1) activation during unimanual hand movements and hemispheric asymmetry changed after motor skill learning. Eleven right-handed participants preformed a two-ball-rotation motor task with the right and the left hand, separately, in all experimental sessions. Before and after exercise sessions, the degree of ipsilateral M1 activation during brief execution of the motor task was measured as changes in the size of motor-evoked potentials (MEPs) of the thenar and the first dorsal interosseous muscle of the nontask hand using transcranial magnetic stimulation. Before exercise, MEPs of the nontask hand were significantly facilitated on both sides during the motor task. After exercise, facilitation of MEPs of the nontask hand during the motor task was significantly reduced for the right hand (thenar: P=0.014, first dorsal interosseous: P=0.022) but not for the left hand. We conclude that ipsilateral M1 activation, associated with a complex motor task, is first symmetrical in both hemispheres. However, on exercise, ipsilateral activation is reduced only in left M1, indicating a stronger learning-dependent modification of motor networks within the left hemisphere.

Functional plasticity of surround inhibition in the motor cortex during single finger contraction training.

We investigated the functional changes in short intracortical inhibitory (SICI) circuits to determine whether surround inhibition is altered during a simple finger movement training. Using an electromyographic (EMG) feedback system linked to a computer monitor, participants practiced sustained index finger abduction by 40% maximum voluntary contraction of the first dorsal interosseous (FDI) while decreasing overflow EMG activity of the abductor digiti minimi (ADM) to less than 5% maximum voluntary contraction. Single transcranial magnetic stimuli (TMS) and paired-pulse TMS were applied to the left primary motor cortex to elicit motor-evoked potentials (MEPs) in the right FDI and ADM before/after training. In addition to recording MEPs from both muscles during voluntary FDI contraction, MEPs were recorded during motor imagery. MEPs from the FDI were not altered by training, indicating no functional changes in SICI circuits associated with the FDI field. In contrast, SICI circuits associated with ADM were significantly strengthened by training, as indicated by reduced baseline EMG activity during both actual FDI contraction and motor imagery and by reduced MEPs in response to post-training TMS. We propose that SICI circuits show functional plasticity during motor training and that surround circuit inhibition of nontarget muscle groups increases in proportion to the acquisition of motor skills.

Changes of excitability in M1 induced by neuromuscular electrical stimulation differ between presence and absence of voluntary drive.

The aim of this study is to investigate excitability changes in the human motor cortex induced by variable therapeutic electrical stimulations (TESs) with or without voluntary drive. We recorded motor-evoked potentials (MEPs) from extensor and flexor carpi radialis (FCR) muscles at rest and during FCR muscle contraction after the application of TES on FCR. TES application conditions were changed intensities, frequencies, and trains. In addition, to evaluate the contribution of M1 inhibitory circuits to the effects of TES application, we also recorded MEPs using paired-pulse transcranial magnetic stimulation. In resting muscle states, an increase in TES intensity resulted in an increase in MEP ratio in both the muscles. In contrast, when TES was applied to FCR during contraction, MEP ratios of both the muscles decreased with increased number of pulse trains. However, under both the states, MEP ratios decreased induced by paired-pulse transcranial magnetic stimulation in extensor carpi radialis to which TES was not applied. Excitability changes in M1 induced by TES application were reversibly modulated depending on the presence or absence of voluntary drive. This study showed that the therapy and the voluntary drive of the target muscles act together, and complement the effects of each other, which may be beneficial for optimizing the rehabilitation if the therapy accompanies voluntary drive.