Evidence for facilitation of motor evoked potentials (MEPs) induced by motor imagery

Electroencephalographic responses before, during, and after upper limb paired associative stimulation

Paired associative stimulation (PAS) is a non-invasive protocol involving repeated stimulus pairs to activate two cortical areas alternately, inducing Hebbian-like plasticity. However, its neurophysiological impacts remain unclear. To determine the changes that occur in the brain during PAS, brain activity during PAS must be measured and distinguished from the electromagnetic artifacts produced by the stimulation. Here, we present a novel dataset of electroencephalography (EEG) measurements during PAS with an inter-stimulus-interval of 25 ms (PAS25, expected to induce long-term potentiation-like changes) or 35 ms (PAS35, no expected change). This dataset includes raw data and pre-processed data with electromagnetic artefacts removed. The right ulnar nerve's electrical stimulation preceded transcranial magnetic stimulation to the left primary motor cortex in both cases. EEG was measured before and after the PAS sessions, with only electrical or magnetic stimulation. To demonstrate the quality of the data, we summarize the stability of the stimulation site and the event-related potentials before, during, and after PAS. This dataset will enable observing brain dynamics due to the accumulation of stimulations during PAS and differences in responsiveness to stimulations before and after PAS.

Age bias in changes in finger dexterity based on brain activation and spinal motor nerve excitability induced by motor imagery practice

Elderly adults may have poorer recall ability than young adults and may not fully enjoy the effects of motor imagery. To understand the age bias of the effect of motor imagery on hand dexterity, we evaluated brain activation and spinal motor nerve excitability. Brain activation was evaluated from changes in oxygenated hemoglobin concentration, while spinal motor nerve excitability was evaluated from F-waves in eight young (mean age 21.0 ± 0.5 years) and eight elderly (mean age 69.5 ± 2.3 years) subjects of matched sex ratio at rest and during motor imagery. Purdue Pegboard scores were also measured before and after motor imagery, and changes in hand dexterity were assessed. The results showed that motor imagery improved hand dexterity without an age bias, and in a similar trend, spinal motor nerve excitability increased during motor imagery. Functional brain connectivity analysis showed the formation of a working memory network in both groups. However, in the analysis of single brain region activation, the young group, but not the elderly group, showed increased activity in the supplementary motor cortex during motor imagery. In addition, regardless of age-related changes, causal coupling indicated the supplementary motor cortex was associated with the changes of spinal motor nerve excitability. Although the changes in brain activation during motor imagery were influenced by age, motor imagery-induced improvements in hand dexterity are also expected in the elderly. Furthermore, changes in spinal motor nerve excitability may be useful in determining the qualitative aspects of motor imagery.

Cognitive effect of passively induced kinesthetic perception associated with virtual body augmentation modulates spinal reflex

The virtual movement of an augmented body, perceived as part of oneself, forms the basis of kinesthetic perception induced by visual stimulation (KINVIS). KINVIS is a visually induced virtual kinesthetic perception that clinically suppresses spasticity. The present study hypothesized that central neural network activity during KINVIS affects subcortical neural circuits. The present study aimed to elucidate whether reciprocal and presynaptic inhibition occurs during KINVIS. Seventeen healthy participants were recruited (mean age: 27.9 ± 3.6 yr), and their soleus Hoffmann-reflexes (H-reflexes) were recorded by peripheral nerve stimulation while perceiving the dorsiflexion kinesthetic illusion in the right-side foot (seated in a comfortable chair). Two control conditions were set to observe the same foot video without the kinesthetic illusion while focusing on the static foot image. Unconditioned H-reflex and two types of conditioned H-reflexes were measured: Ia (reciprocal inhibition) and D1 (presynaptic inhibition). Reciprocal Ia and D1 inhibition of the soleus muscle was significantly enhanced during the kinesthetic illusion compared with the condition without kinesthetic illusion (a post hoc analysis using the Bonferroni test: Ia inhibition, P = 0.002; D1 inhibition, P = 0.049). This study indicates that kinesthetic illusion elicits an inhibitory effect on the monosynaptic reflex loop of Ia afferents, potentially inhibiting the hyperexcitability of the stretch reflex. These findings demonstrate that brain activity associated with visually induced kinesthetic illusions acts on spinal inhibition circuits. These insights may be valuable in clinical rehabilitation practice, specifically for the treatment of spasticity.NEW & NOTEWORTHY Neural effects in visual-induced kinesthetic illusion expand into the spinal reflex. Kinesthetic illusion inhibits the monosynaptic reflex in an antagonistic muscle via reciprocal and presynaptic inhibition. Visually induced kinesthetic illusion is a suitable treatment for spasticity in patients with stroke.

Tactile versus motor imagery: differences in corticospinal excitability assessed with single-pulse TMS

Tactile Imagery (TI) remains a fairly understudied phenomenon despite growing attention to this topic in recent years. Here, we investigated the effects of TI on corticospinal excitability by measuring motor evoked potentials (MEPs) induced by single-pulse transcranial magnetic stimulation (TMS). The effects of TI were compared with those of tactile stimulation (TS) and kinesthetic motor imagery (kMI). Twenty-two participants performed three tasks in randomly assigned order: imagine finger tapping (kMI); experience vibratory sensations in the middle finger (TS); and mentally reproduce the sensation of vibration (TI). MEPs increased during both kMI and TI, with a stronger increase for kMI. No statistically significant change in MEP was observed during TS. The demonstrated differential effects of kMI, TI and TS on corticospinal excitability have practical implications for devising the imagery-based and TS-based brain-computer interfaces (BCIs), particularly the ones intended to improve neurorehabilitation by evoking plasticity changes in sensorimotor circuitry.

Multisensory subtypes of aphantasia: Mental imagery as supramodal perception in reverse

Cognitive neuroscience research on mental imagery has largely focused on the visual imagery modality in unimodal task contexts. Recent studies have uncovered striking individual differences in visual imagery capacity, with some individuals reporting a subjective absence of conscious visual imagery ability altogether ("aphantasia"). However, naturalistic mental imagery is often multi-sensory, and preliminary findings suggest that many individuals with aphantasia also report a subjective lack of mental imagery in other sensory domains (such as auditory or olfactory imagery). In this paper, we perform a series of cluster analyses on the multi-sensory imagery questionnaire scores of two large groups of aphantasic subjects, defining latent sub-groups in this sample population. We demonstrate that aphantasia is a heterogenous phenomenon characterised by dominant sub-groups of individuals with visual aphantasia (those who report selective visual imagery absence) and multi-sensory aphantasia (those who report an inability to generate conscious mental imagery in any sensory modality). We replicate our findings in a second large sample and show that more unique aphantasia sub-types also exist, such as individuals with selectively preserved mental imagery in only one sensory modality (e.g. intact auditory imagery). We outline the implications of our findings for network theories of mental imagery, discussing how unique aphantasia aetiologies with distinct self-report patterns might reveal alterations to various levels of the sensory processing hierarchy implicated in mental imagery.

Explicit and implicit motor simulations are impaired in individuals with aphantasia

Individuals with aphantasia report having difficulties or an inability to generate visual images of objects or events. So far, there is no evidence showing that this condition also impacts the motor system and the generation of motor simulations. We probed the neurophysiological marker of aphantasia during explicit and implicit forms of motor simulation, i.e. motor imagery and action observation, respectively. We tested a group of individuals without any reported imagery deficits (phantasics) as well as a group of individuals self-reporting the inability to mentally simulate images or movements (aphantasics). We instructed the participants to explicitly imagine a maximal pinch movement in the visual and kinaesthetic modalities and to observe a video showing a pinch movement. By means of transcranial magnetic stimulation, we triggered motor-evoked potentials in the target right index finger. As expected, the amplitude of motor-evoked potentials, a marker of corticospinal excitability, increased for phantasics during kinaesthetic motor imagery and action observation relative to rest but not during visual motor imagery. Interestingly, the amplitude of motor-evoked potentials did not increase in any of the conditions for the group of aphantasics. This result provides neurophysiological evidence that individuals living with aphantasia have a real deficit in activating the motor system during motor simulations.

Modulation of lower limb muscle corticospinal excitability during various types of motor imagery

Motor imagery (MI) is used for rehabilitation and sports training. Previous studies focusing on the upper limb have investigated the effects of MI on corticospinal excitability in the muscles involved in the imagined movement (i.e., the agonist muscles). The present study focused on several lower-limb movements and investigated the influences of MI on corticospinal excitability in the lower limb muscles. Twelve healthy individuals (ten male and two female individuals) participated in this study. Motor-evoked potentials (MEP) from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and soleus (SOL) muscles were elicited through transcranial magnetic stimulation (TMS) to the primary motor cortex during MI of knee extension, knee flexion, ankle dorsiflexion, and ankle plantarflexion and at rest. The results showed that the RF MEPs were significantly increased during MI in knee extension, ankle dorsiflexion, and ankle plantarflexion but not in knee flexion, compared with those at rest. The TA MEPs were significantly increased during MI in knee extension and foot dorsiflexion, while MEPs were not significantly different during MI in knee flexion and foot dorsiflexion than those at rest. For the BF and SOL muscles, there was no significant MEP modulation in either MI. These results demonstrated that corticospinal excitability of the RF and TA muscles was facilitated during MI of movements in which they are active and during MI of lower-limb movements in which they are not involved. On the contrary, corticospinal excitability of the BF and SOL muscles was not facilitated by MI of lower-limb movements. These results suggest that facilitation of corticospinal excitability depends on the muscle and the type of lower-limb MI.

Relationship between resting-state functional connectivity and change in motor function after motor imagery intervention in patients with stroke: a scoping review

BACKGROUND

In clinical practice, motor imagery has been proposed as a treatment modality for stroke owing to its feasibility in patients with severe motor impairment. Motor imagery-based interventions can be categorized as open- or closed-loop. Closed-loop intervention is based on voluntary motor imagery and induced peripheral sensory afferent (e.g., Brain Computer Interface (BCI)-based interventions). Meanwhile, open-loop interventions include methods without voluntary motor imagery or sensory afferent. Resting-state functional connectivity (rs-FC) is defined as a significant temporal correlated signal among functionally related brain regions without any stimulus. rs-FC is a powerful tool for exploring the baseline characteristics of brain connectivity. Previous studies reported changes in rs-FC after motor imagery interventions. Systematic reviews also reported the effects of motor imagery-based interventions at the behavioral level. This study aimed to review and describe the relationship between the improvement in motor function and changes in rs-FC after motor imagery in patients with stroke.

REVIEW PROCESS

The literature review was based on Arksey and O'Malley's framework. PubMed, Ovid MEDLINE, Cochrane Central Register of Controlled Trials, and Web of Science were searched up to September 30, 2023. The included studies covered the following topics: illusion without voluntary action, motor imagery, action imitation, and BCI-based interventions. The correlation between rs-FC and motor function before and after the intervention was analyzed. After screening by two independent researchers, 13 studies on BCI-based intervention, motor imagery intervention, and kinesthetic illusion induced by visual stimulation therapy were included.

CONCLUSION

All studies relating to motor imagery in this review reported improvement in motor function post-intervention. Furthermore, all those studies demonstrated a significant relationship between the change in motor function and rs-FC (e.g., sensorimotor network and parietal cortex).

Transcranial magnetic stimulation of the brain: What is stimulated? - A consensus and critical position paper

Transcranial (electro)magnetic stimulation (TMS) is currently the method of choice to non-invasively induce neural activity in the human brain. A single transcranial stimulus induces a time-varying electric field in the brain that may evoke action potentials in cortical neurons. The spatial relationship between the locally induced electric field and the stimulated neurons determines axonal depolarization. The induced electric field is influenced by the conductive properties of the tissue compartments and is strongest in the superficial parts of the targeted cortical gyri and underlying white matter. TMS likely targets axons of both excitatory and inhibitory neurons. The propensity of individual axons to fire an action potential in response to TMS depends on their geometry, myelination and spatial relation to the imposed electric field and the physiological state of the neuron. The latter is determined by its transsynaptic dendritic and somatic inputs, intrinsic membrane potential and firing rate. Modeling work suggests that the primary target of TMS is axonal terminals in the crown top and lip regions of cortical gyri. The induced electric field may additionally excite bends of myelinated axons in the juxtacortical white matter below the gyral crown. Neuronal excitation spreads ortho- and antidromically along the stimulated axons and causes secondary excitation of connected neuronal populations within local intracortical microcircuits in the target area. Axonal and transsynaptic spread of excitation also occurs along cortico-cortical and cortico-subcortical connections, impacting on neuronal activity in the targeted network. Both local and remote neural excitation depend critically on the functional state of the stimulated target area and network. TMS also causes substantial direct co-stimulation of the peripheral nervous system. Peripheral co-excitation propagates centrally in auditory and somatosensory networks, but also produces brain responses in other networks subserving multisensory integration, orienting or arousal. The complexity of the response to TMS warrants cautious interpretation of its physiological and behavioural consequences, and a deeper understanding of the mechanistic underpinnings of TMS will be critical for advancing it as a scientific and therapeutic tool.

Imagined paralysis reduces motor cortex excitability

Mental imagery is a powerful capability that engages similar neurophysiological processes that underlie real sensory and motor experiences. Previous studies show that motor cortical excitability can increase during mental imagery of actions. In this study, we focused on possible inhibitory effects of mental imagery on motor functions. We assessed whether imagined arm paralysis modulates motor cortical excitability in healthy participants, as measured by motor evoked potentials (MEPs) of the hand induced by near-threshold transcranial magnetic stimulation (TMS) over the primary motor cortex hand area. We found lower MEP amplitudes during imagined arm paralysis when compared to imagined leg paralysis or baseline stimulation without paralysis imagery. These results show that purely imagined bodily constraints can selectively inhibit basic motor corticospinal functions. The results are discussed in the context of motoric embodiment/disembodiment.

Thenar Muscle Motor Imagery Increases Spinal Motor Neuron Excitability of the Abductor Digiti Minimi Muscle

When a person attempts intended finger movements, unintended finger movement also occur, a phenomenon called “enslaving”. Given that motor imagery (MI) and motor execution (ME) share a common neural foundation, we hypothesized that the enslaving effect on the spinal motor neuron excitability occurs during MI. To investigate this hypothesis, electromyography (EMG) and F-wave analysis were conducted in 11 healthy male volunteers. Initially, the EMG activity of the left abductor digiti minimi (ADM) muscle during isometric opposition pinch movement by the left thumb and index finger at 50% maximal effort was compared with EMG activity during the Rest condition. Next, the F-wave and background EMG recordings were performed under the Rest condition, followed by the MI condition. Specifically, in the Rest condition, subjects maintained relaxation. In the MI condition, they imagined isometric left thenar muscle activity at 50% maximal voluntary contraction (MVC). During ME, ADM muscle activity was confirmed. During the MI condition, both F-wave persistence and the F-wave/M-wave amplitude ratio obtained from the ADM muscle were significantly increased compared with that obtained during the Rest condition. No difference was observed in the background EMG between the Rest and MI conditions. These results suggest that MI of isometric intended finger muscle activity at 50% MVC facilitates spinal motor neuron excitability corresponding to unintended finger muscle. Furthermore, MI may induce similar modulation of spinal motor neuron excitability as actual movement.

Corticospinal Excitability of the Lower Limb Muscles During the Anticipatory Postural Adjustments: A TMS Study During Dart Throwing

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.

The effects of physical training versus combined action observation and motor imagery in conjunction with physical training on upper-extremity performance

INTRODUCTION

Combined action observation and motor imagery training (AO+MI training), which involves motor imagery during action observation and physical training, has been attracting attention as an effective strategy for learning motor skills. However, little has been reported on the effects of AO+MI training. In the present study, we compared the effects of AO+MI training to the effects of physical training on upper-extremity performance.

MATERIALS AND METHODS

Ninety-six healthy participants were randomly assigned to either the control group or the experimental group. Sport stacking, which is often used to evaluate upper-extremity performance, was adopted for the task. The experiment was scheduled for three days. The training was 20 min per day. The control group performed only physical training, while the experimental group performed four 5-min AO+MI training sessions. Time taken to complete a sport stacking try (task completion time) was defined as the index of speed of upper-extremity performance and number of fallen cups as the index of its accuracy. The outcomes within each group and between the two groups were compared.

RESULTS

Both AO+MI training and physical training showed reduced task completion time and increased number of fallen cups. There were no significant differences in the degree of changes between the groups.

CONCLUSION

Results from the present study showed that AO+MI training and physical training had almost the same influence on upper-extremity performance in the early stages of learning sport stacking. This result suggests that AO+MI training may be an effective and low-burden training method for participants.

A BCI-Based Vibrotactile Neurofeedback Training Improves Motor Cortical Excitability During Motor Imagery

In this study, we address the issue of whether vibrotactile feedback can enhance the motor cortex excitability translated into the plastic changes in local cortical areas during motor imagery (MI) BCI-based training. For this purpose, we focused on two of the most notable neurophysiological effects of MI - the event-related desynchronization (ERD) level and the increase in cortical excitability assessed with navigated transcranial magnetic stimulation (nTMS). For TMS navigation, we used individual high-resolution 3D brain MRIs. Ten BCI-naive and healthy adults participated in this study. The MI (rest or left/right hand imagery using Graz-BCI paradigm) tasks were performed separately in the presence and absence of feedback. To investigate how much the presence/absence of vibrotactile feedback in MI BCI-based training could contribute to the sensorimotor cortical activations, we compared the MEPs amplitude during MI after training with and without feedback. In addition, the ERD levels during MI BCI-based training were investigated. Our findings provide evidence that applying vibrotactile feedback during MI training leads to (i) an enhancement of the desynchronization level of mu-rhythm EEG patterns over the contralateral motor cortex area corresponding to the MI of the non-dominant hand; (ii) an increase in motor cortical excitability in hand muscle representation corresponding to a muscle engaged by the MI.

Mental individuation of imagined finger movements can be achieved using TMS-based neurofeedback

Neurofeedback (NF) in combination with motor imagery (MI) can be used for training individuals to volitionally modulate sensorimotor activity without producing overt movements. However, until now, NF methods were of limited utility for mentally training specific hand and finger actions. Here we employed a novel transcranial magnetic stimulation (TMS) based protocol to probe and detect MI-induced motor activity patterns in the primary motor cortex (M1) with the aim to reinforce selective facilitation of single finger representations. We showed that TMS-NF training but not MI training with uninformative feedback enabled participants to selectively upregulate corticomotor excitability of one finger, while simultaneously downregulating excitability of other finger representations within the same hand. Successful finger individuation during MI was accompanied by strong desynchronization of sensorimotor brain rhythms, particularly in the beta band, as measured by electroencephalography. Additionally, informative TMS-NF promoted more dissociable EEG activation patterns underlying single finger MI, when compared to MI of the control group where no such feedback was provided. Our findings suggest that selective TMS-NF is a new approach for acquiring the ability of finger individuation even if no overt movements are performed. This might offer new treatment modality for rehabilitation after stroke or spinal cord injury.

Comparison of the on-line effects of different motor simulation conditions on corticospinal excitability in healthy participants

In healthy participants, corticospinal excitability is known to increase during motor simulations such as motor imagery (MI), action observation (AO) and mirror therapy (MT), suggesting their interest to promote plasticity in neurorehabilitation. Further comparing these methods and investigating their combination may potentially provide clues to optimize their use in patients. To this end, we compared in 18 healthy participants abductor pollicis brevis (APB) corticospinal excitability during MI, AO or MT, as well as MI combined with either AO or MT. In each condition, 15 motor-evoked potentials (MEPs) and three maximal M-wave were elicited in the right APB. Compared to the control condition, mean normalized MEP amplitude (i.e. MEP/M) increased during MI (P = .003), MT (P < .001) and MT + MI (P < .001), without any difference between the three conditions. No MEP modulation was evidenced during AO or AO + MI. Because MI provided no additional influence when combined with AO or MT, our results may suggest that, in healthy subjects, visual feedback and unilateral movement with a mirror may provide the greatest effects among all the tested motor simulations.

Effect of repetitive peripheral magnetic stimulation combined with motor imagery on the corticospinal excitability of antagonist muscles

OBJECTIVE

Repetitive peripheral magnetic stimulation (rPMS) combined with motor imagery facilitates the corticospinal excitability of the agonist muscles. However, the effects of rPMS combined with motor imagery on the corticospinal excitability of the antagonist muscles are unclear. This is an important aspect for applying rPMS in neurorehabilitation for sensorimotor dysfunction. Therefore, we investigated the real-time changes of corticospinal excitability of antagonist muscles during rPMS combined with motor imagery.

METHODS

Fourteen healthy volunteers underwent four different experimental conditions: rest, rPMS, motor imagery, and rPMS combined with motor imagery (rPMS + motor imagery). In the rPMS and rPMS + motor imagery conditions, rPMS (25 Hz, 1600 ms/train, 1.5× of the motor threshold) was delivered to the dorsal side of the forearm. In motor imagery and rPMS + motor imagery, the participant imagined wrist extension movements. Transcranial magnetic stimulation was delivered to record motor-evoked potentials of the antagonist muscle during experimental interventions.

RESULTS

The motor-evoked potential (normalized by rest condition) values indicated no difference between rPMS, motor imagery, and rPMS + motor imagery.

CONCLUSION

These results suggest that rPMS combined with motor imagery has no effect on the corticospinal excitability of the antagonist muscles and highlight the importance of investigating the effects of rPMS combined with motor imagery at the spinal level.

Muscle-specific movement-phase-dependent modulation of corticospinal excitability during upper-limb motor execution and motor imagery combined with virtual action observation

Corticospinal excitability in humans can be facilitated during imagination and/or observation of upper-limb motor tasks. However, it remains unclear to what extent facilitation levels may differ from those elicited during execution of the same tasks. Twelve able-bodied individuals were recruited in this study. Motor evoked potentials (MEPs) in extensor carpi radialis (ECR) and flexor carpi radialis (FCR) muscles were elicited through transcranial magnetic stimulation of the primary motor cortex during: (i) rest; (ii) wrist extension; and (iii) wrist flexion. Responses were compared between: (1) motor imagery combined with virtual action observation (MI + AO; first-person virtual wrist movements shown on a computer display, while participants remained at rest and imagined these movements); and (2) motor execution (ME; participants extended or flexed their wrist). During MI + AO, ECR MEPs were facilitated during the extension phase but not the flexion phase, while FCR MEPs were facilitated during the flexion phase but not extension phase, compared to rest. During the ME condition, same, but greater, modulations were shown as those during MI + AO, while background muscle activities were similar in the rest phase as during extension and flexion phase in the MI + AO condition. Our results demonstrated that kinesthetic MI that included imagination and observation of virtual hands can elicit phase-dependent muscles-specific corticospinal facilitation of wrist muscles, consistent to those during actual hand extension and flexion. Moreover, we showed that MI + AO can contribute considerably to the overall corticospinal facilitation (∼20 % of ME) even without muscle contractions. These findings support utility of computer graphics-based motor imagery, which may have implications for rehabilitation and development of brain-computer interfaces.

Hemodynamic Signal Changes During Motor Imagery Task Performance Are Associated With the Degree of Motor Task Learning

Purpose

This study aimed to investigate whether oxygenated hemoglobin (oxy-Hb) generated during a motor imagery (MI) task is associated with the motor learning level of the task.

Methods

We included 16 right-handed healthy participants who were trained to perform a ball rotation (BR) task. Hemodynamic brain activity was measured using near-infrared spectroscopy to monitor changes in oxy-Hb concentration during the BR MI task. The experimental protocol used a block design, and measurements were performed three times before and after the initial training of the BR task as well as after the final training. The BR count during training was also measured. Furthermore, subjective vividness of MI was evaluated three times after NIRS measurement using the Visual Analog Scale (VAS).

Results

The results showed that the number of BRs increased significantly with training (P < 0.001). VAS scores also improved with training (P < 0.001). Furthermore, oxy-Hb concentration and the region of interest (ROI) showed a main effect (P = 0.001). An interaction was confirmed (P < 0.001), and it was ascertained that the change in oxy-Hb concentrations due to training was different for each ROI. The most significant predictor of subjective MI vividness was supplementary motor area (SMA) oxy-Hb concentration (coefficient = 0.365).

Discussion

Hemodynamic brain activity during MI tasks may be correlated with task motor learning levels, since significant changes in oxy-Hb concentrations were observed following initial and final training in the SMA. In particular, hemodynamic brain activity in the SMA was suggested to reflect the MI vividness of participants.

Precision pinch force control via brain and spinal motor neuron excitability during motor imagery

This study presents a novel approach for identifying neural substrates underlying the beneficial effects of motor imagery. For motor imagery, participants were instructed to imagine contraction of the left thenar muscle at 50 % maximal voluntary contraction (MVC). The participants then performed isometric contractions of the thumb and index finger at 50 % MVC as accurately as possible after motor imagery and without motor imagery. F-waves and oxygen-hemoglobin levels were examined with and without motor imagery relative to the resting condition. These data were analyzed using structural equation modeling. The degree of changes in the excitability of spinal motor neurons using F-waves during motor imagery may be modulated by inputs from the supplementary motor area. F-waves were analyzed with respect to persistence and the F-wave/maximum M-wave amplitude ratio. We found an association between precision pinch force control after motor imagery and spinal motor neuron excitability during motor imagery. The excitability of the supplementary motor area was not directly associated with precision pinch force control. However, spinal motor neuron excitability was adjusted by the supplementary motor area. Thus, the ability to perform precision pinch force control may be influenced by the supplementary motor area through the excitability of spinal motor neurons.

Neural Basis and Motor Imagery Intervention Methodology Based on Neuroimaging Studies in Children With Developmental Coordination Disorders: A Review

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.

Kinesthetic illusion induced by visual stimulation influences sensorimotor event-related desynchronization in stroke patients with severe upper-limb paralysis: A pilot study

BACKGROUND

Repetition of motor imagery improves the motor function of patients with stroke. However, patients who develop severe upper-limb paralysis after chronic stroke often have an impaired ability to induce motor imagery. We have developed a method to passively induce kinesthetic perception using visual stimulation (kinesthetic illusion induced by visual stimulation [KINVIS]).

OBJECTIVE

This pilot study further investigated the effectiveness of KINVIS in improving the induction of kinesthetic motor imagery in patients with severe upper-limb paralysis after stroke.

METHODS

Twenty participants (11 with right hemiplegia and 9 with left hemiplegia; mean time from onset [±standard deviation], 67.0±57.2 months) with severe upper-limb paralysis who could not extend their paretic fingers were included in this study. The ability to induce motor imagery was evaluated using the event-related desynchronization (ERD) recorded during motor imagery before and after the application of KINVIS for 20 min. The alpha- and beta-band ERDs around the premotor, primary sensorimotor, and posterior parietal cortices of the affected and unaffected hemispheres were evaluated during kinesthetic motor imagery of finger extension and before and after the intervention.

RESULTS

Beta-band ERD recorded from the affected hemisphere around the sensorimotor area showed a significant increase after the intervention, while the other ERDs remained unchanged.

CONCLUSIONS

In patients with chronic stroke who were unable to extend their paretic fingers for a prolonged period of time, the application of KINVIS, which evokes kinesthetic perception, improved their ability to induce motor imagery. Our findings suggest that although KINVIS is a passive intervention, its short-term application can induce changes related to the motor output system.

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.

State-Dependent Gain Modulation of Spinal Motor Output

Afferent somatosensory information plays a crucial role in modulating efferent motor output. A better understanding of this sensorimotor interplay may inform the design of neurorehabilitation interfaces. Current neurotechnological approaches that address motor restoration after trauma or stroke combine motor imagery (MI) and contingent somatosensory feedback, e.g., via peripheral stimulation, to induce corticospinal reorganization. These interventions may, however, change the motor output already at the spinal level dependent on alterations of the afferent input. Neuromuscular electrical stimulation (NMES) was combined with measurements of wrist deflection using a kinematic glove during either MI or rest. We investigated 360 NMES bursts to the right forearm of 12 healthy subjects at two frequencies (30 and 100 Hz) in random order. For each frequency, stimulation was assessed at nine intensities. Measuring the induced wrist deflection across different intensities allowed us to estimate the input-output curve (IOC) of the spinal motor output. MI decreased the slope of the IOC independent of the stimulation frequency. NMES with 100 Hz vs. 30 Hz decreased the threshold of the IOC. Human-machine interfaces for neurorehabilitation that combine MI and NMES need to consider bidirectional communication and may utilize the gain modulation of spinal circuitries by applying low-intensity, high-frequency stimulation.

The Vividness of Motor Imagery Is Correlated With Corticospinal Excitability During Combined Motor Imagery and Action Observation

The present study aimed to investigate the relationship between motor imagery (MI) assessment (ability and quality) and neurophysiological assessment [transcranial magnetic stimulation (TMS)-induced motor-evoked potentials (MEPs)] during combined MI and action observation (AO; MI + AO). Sixteen subjects completed an MI task playing the piano with both hands, and neurophysiological assessment was performed during the MI task. The Movement Imagery Questionnaire-Revised was adopted to evaluate MI ability, while the visual analogue scale (VAS) was adopted to evaluate MI quality. A TMS pulse was delivered during the MI task, and MEPs were subsequently recorded in the abductor pollicis brevis (APB). We found a significant positive correlation between the VAS score and the TMS-induced MEPs (ρ = 0.497, p < 0.001). These findings suggest that the VAS score could potentially reflect the corticospinal excitability during MI + AO, particularly in complex MI tasks.

Interlimb neural interactions in corticospinal and spinal reflex circuits during preparation and execution of isometric elbow flexion

We found that upper limb muscle contractions facilitated corticospinal circuits controlling lower limb muscles even during motor preparation, whereas motor execution of the task was required to facilitate spinal circuits. We also found that facilitation did not depend on whether contralateral or ipsilateral hands were contracted or if they were contracted bilaterally. Overall, these findings suggest that training of unaffected upper limbs may be useful to enhance facilitation of affected lower limbs in paraplegic individuals.

Motor imagery enhances corticospinal transmission mediated by cervical premotoneurons in humans

Imaging movement has positive effects on the reacquisition of motor functions after damage to the central nervous system. This study shows that motor imagery facilitates oligosynaptic corticospinal excitation that is mediated via cervical premotoneurons, which may be important for motor recovery in monkeys and humans. Current findings highlight how this imagery might be a beneficial tool for movement disorders through effects on premotoneuron circuitry.

Optimal stimulation parameters for spinal and corticospinal excitabilities during contraction, motor imagery and rest: A pilot study

Objectives

It is commonly accepted that motor imagery (MI), i.e. the mental simulation of a movement, leads to an increased size of cortical motor evoked potentials (MEPs), although the magnitude of this effect differs between studies. Its impact on the spinal level is even more variable in the literature. Such discrepancies may be explained by many different experimental approaches. Therefore, the question of the optimal stimulation parameters to assess both spinal and corticospinal excitabilities remains open.

Methods

H-reflexes and MEPs of the triceps surae were evoked in 11 healthy subjects during MI, weak voluntary contraction (CON) and rest (REST). In each condition, the full recruitment curve from the response threshold to maximal potential was investigated.

Results

At stimulation intensities close to the maximal response, MEP amplitude was increased by CON compared to REST on the triceps surae. No effect of the different conditions was found on the H-reflex recruitment curve, except a small variation beyond maximal H-reflex in the soleus muscle.

Conclusion

Based on our results, we recommend to assess corticospinal excitability between 70% and 100% of maximal MEP intensity instead of the classical use of a percentage of the motor threshold and to elicit H-reflexes on the ascending part of the recruitment curve.

Probing the Effect of Block Duration on Corticospinal Excitability during Motor Imagery Performance

Considerable evidence exists related to the behavioral outcomes of motor imagery-based training (MI). Comparatively, there is a relative gap in the literature on how corticospinal excitability, a precursor for experience-dependent plasticity, changes over the course of an MI session, and more specifically if there is an effect of varying the duration of the blocks in which MI is performed. As such, we probed corticospinal excitability during MI, whereby the duration of MI blocks within the session were manipulated yet total exposure to MI was kept constant. Participants performed a total of 24 min of MI of common motor tasks in blocks of 2, 4 or 6 min. Transcranial magnetic stimulation was used to assess corticospinal excitability throughout MI performance. All groups demonstrated increased corticospinal excitability over the session. Owing to a decrease in corticospinal excitability when engaging in 6 min blocks and the variability noted when engaging in 2 min blocks, findings suggest that MI performed in 4 min blocks may be preferable for the generation and maintenance of corticospinal excitability, at least relative to 2 and 6 min blocks. Overall, our findings provide physiological evidence that informs the structure of MI training sessions to optimize their effectiveness.

Induction of plasticity in the human motor system by motor imagery and transcranial magnetic stimulation

KEY POINTS

Delivering transcranial magnetic brain stimulation over the motor cortex during motor imagination leads to enhanced motor output, which is selective for the muscles primarily involved in the imagined movement. This novel protocol may be useful to enhance function after damage to the motor system, such as after stroke.

ABSTRACT

Several paired stimulation paradigms are known to induce plasticity in the motor cortex, reflected by changes in the motor evoked potential (MEP) following the paired stimulation. Motor imagery (MI) is capable of activating the motor system and affecting cortical excitability. We hypothesized that it might be possible to use MI in conjunction with transcranial magnetic stimulation (TMS) to induce plasticity in the human motor system. TMS was delivered to the motor cortex of healthy human subjects, and baseline MEPs recorded from forearm flexor, forearm extensor and intrinsic hand muscles. Subjects were then asked to imagine either wrist flexion or extension movements during TMS delivery (n = 90 trials). Immediately after this intervention, MEP measurement was repeated. Control protocols tested the impact of imagination or TMS alone. Flexion imagination with TMS increased MEPs in flexors and an intrinsic hand muscle. Extensor imagination with TMS increased MEPs in extensor muscles only. The control paradigms did not produce significant changes. We conclude that delivering TMS during MI is capable of inducing plastic changes in the motor system. This new protocol may find utility to enhance functional rehabilitation after brain injury.

Dissociation between cortical and spinal excitability of the antagonist muscle during combined motor imagery and action observation

Inhibitory neural control of antagonist muscle is one of the fundamental neural mechanism of coordinated human limb movement. Previous studies have revealed that motor execution (ME) and motor imagery (MI) share many common neural substrates; however, whether inhibitory neural activity occurs during MI remains unknown. In addition, recent studies have demonstrated that a combined MI and action observation (MI + AO) produces strong neurophysiological changes compared with MI or AO alone. Therefore, we investigated inhibitory changes in cortical and spinal excitability of the antagonist muscle during MI + AO and ME. Single-pulse transcranial magnetic stimulation (TMS) experiments revealed that corticospinal excitability of the antagonist muscle was decreased during MI + AO. Conversely, F-wave experiments showed that F-wave persistence of the antagonist muscle increased. Paired-pulse TMS experiment also demonstrated that short-interval intracortical inhibition (SICI) did not contribute to this inhibition. Therefore, cortical mediated inhibition, except for SICI, may be related to this inhibition. Conversely, such clear inhibition of the antagonist muscle was not observed during ME, presumably owing to the effects of muscle contraction to decelerate the movements and/or sensory input accompanying the joint movements. These findings provide important insights into the neurophysiological differences between MI + AO and ME.

Visual and kinesthetic modes affect motor imagery classification in untrained subjects

The understanding of neurophysiological mechanisms responsible for motor imagery (MI) is essential for the development of brain-computer interfaces (BCI) and bioprosthetics. Our magnetoencephalographic (MEG) experiments with voluntary participants confirm the existence of two types of motor imagery, kinesthetic imagery (KI) and visual imagery (VI), distinguished by activation and inhibition of different brain areas in motor-related α- and β-frequency regions. Although the brain activity corresponding to MI is usually observed in specially trained subjects or athletes, we show that it is also possible to identify particular features of MI in untrained subjects. Similar to real movement, KI implies muscular sensation when performing an imaginary moving action that leads to event-related desynchronization (ERD) of motor-associated brain rhythms. By contrast, VI refers to visualization of the corresponding action that results in event-related synchronization (ERS) of α- and β-wave activity. A notable difference between KI and VI groups occurs in the frontal brain area. In particular, the analysis of evoked responses shows that in all KI subjects the activity in the frontal cortex is suppressed during MI, while in the VI subjects the frontal cortex is always active. The accuracy in classification of left-arm and right-arm MI using artificial intelligence is similar for KI and VI. Since untrained subjects usually demonstrate the VI imagery mode, the possibility to increase the accuracy for VI is in demand for BCIs. The application of artificial neural networks allows us to classify MI in raising right and left arms with average accuracy of 70% for both KI and VI using appropriate filtration of input signals. The same average accuracy is achieved by optimizing MEG channels and reducing their number to only 13.

Imagery strategy affects spinal motor neuron excitability: using kinesthetic and somatosensory imagery

Motor imagery is the mental rehearsal of a movement within working memory. Reduction of spinal motor neuron excitability has been demonstrated after stroke, and motor imagery may increase spinal motor neuron excitability in patients with a motor deficit. However, spinal motor neuron excitability varies depending on the imagery strategy used. In this study, we examined spinal motor neuron excitability during kinesthetic, somatosensory, and combined imagery. Healthy adult volunteers (n=14) were recruited for F-wave recording. The F-wave was measured during relaxation to determine baseline levels, followed by measurement during the three imagery trials performed in a random order. In the somatosensory imagery (SI) trial, participants imagined tactile and pressure perception of the thumb finger pulp during holding a pinch meter. In the kinesthetic imagery (KI) trial, participants imagined muscle contraction during isometric thenar muscle activity at 50% maximal voluntary contraction. In the combined KI and SI trial, participants performed the KI and SI simultaneously. After F-wave recording, participants evaluated the difficulty of each imagery trial using a five-point Likert scale. Persistence during SI and KI was significantly higher than that at rest. The F/M amplitude ratio during KI was significantly higher than that at rest. The five-point Likert scale score of the combined KI and SI was significantly lower than that of KI. KI may increase spinal motor neuron excitability over that of SI. Thus, it is important to consider the sensory modality chosen for imagery during rehabilitation.

The Dynamic Duo: Combining noninvasive brain stimulation with cognitive interventions

Pharmacotherapy, psychotherapy, and non-invasive brain stimulation (NIBS)¹ each show efficacy in the treatment of psychiatric disorders; however, more efficacious interventions are needed as reflected by an overall unmet need in mental health care. While each modality has typically been studied and developed as a monotherapy, in practice they are typically used in combination. Research has begun to emerge studying the potential synergistic actions of multi-modal, combination therapies. For example, NIBS combined with rehabilitation strategies have demonstrated some success for speech and motor rehabilitation in stroke patients. In this review we present evidence suggesting that combining NIBS with targeted, cognitive interventions offers a potentially powerful new approach to treating neuropsychiatric disorders. Here we focus on NIBS studies using transcranial direct current stimulation (tDCS)² and transcranial magnetic stimulation (TMS)³ given that these modalities are relatively safe, noninvasive, and can be performed simultaneously with neurocognitive interventions. We review the concept of "state dependent" effects of NIBS and highlight how simultaneous or sequential cognitive interventions could help optimize NIBS therapy by providing further control of ongoing neural activity in targeted neural networks. This review spans a range of neuropsychiatric disorders including major depressive disorder, schizophrenia, generalized anxiety, and autism. For each disorder, we emphasize neuroanatomical circuitry that could be engaged with combination therapy and critically discuss the literature that has begun to emerge. Finally, we present possible underlying mechanisms and propose future research strategies that may further refine the potential of combination therapies.

Spinal plasticity with motor imagery practice

KEY POINTS

While a consensus has now been reached on the effect of motor imagery (MI) - the mental simulation of an action - on motor cortical areas, less is known about its impact on spinal structures. The current study, using H-reflex conditioning paradigms, examined the effect of a 20 min MI practice on several spinal mechanisms of the plantar flexor muscles. We observed modulations of spinal presynaptic circuitry while imagining, which was even more pronounced following an acute session of MI practice. We suggested that the small cortical output generated during MI may reach specific spinal circuits and that repeating MI may increase the sensitivity of the spinal cord to its effects. The short-term plasticity induced by MI practice may include spinal network modulation in addition to cortical reorganization.

ABSTRACT

Kinesthetic motor imagery (MI) is the mental simulation of a movement with its sensory consequences but without its concomitant execution. While the effect of MI practice on cortical areas is well known, its influence on spinal circuitry remains unclear. Here, we assessed plastic changes in spinal structures following an acute MI practice. Thirteen young healthy participants accomplished two experimental sessions: a 20 min MI training consisting of four blocks of 25 imagined maximal isometric plantar flexions, and a 20 min rest (control session). The level of spinal presynaptic inhibition was assessed by conditioning the triceps surae spinal H-reflex with two methods: (i) the stimulation of the common peroneal nerve that induced D1 presynaptic inhibition (H_PSI response), and (ii) the stimulation of the femoral nerve that induced heteronymous Ia facilitation (H_FAC response). We then compared the effects of MI on unconditioned (H_TEST ) and conditioned (H_PSI and H_FAC ) responses before, immediately after and 10 min after the 20 min session. After resting for 20 min, no changes were observed on the recorded parameters. After MI practice, the amplitude of rest H_TEST was unchanged, while H_PSI and H_FAC significantly increased, showing a reduction of presynaptic inhibition with no impact on the afferent-motoneuronal synapse. The current results revealed the acute effect of MI practice on baseline spinal presynaptic inhibition, increasing the sensitivity of the spinal circuitry to MI. These findings will help in understanding the mechanisms of neural plasticity following chronic practice.

Does the duration of motor imagery affect the excitability of spinal anterior horn cells?

PURPOSE

Motor imagery, the process of imagining a physical action, has been shown to facilitate the excitability of spinal anterior horn cells. In the acute phase after a stroke, the excitability of spinal anterior horn cells is significantly reduced, which leads to motor deficits. This loss of movement can be prevented by increasing the excitability of spinal anterior horn cells immediately following an injury. Motor imagery is an effective method for facilitating the excitability of spinal anterior horn cells in patients with impaired movement; however, the optimal duration for motor imagery is unclear.

MATERIALS AND METHODS

To investigate time-dependent changes in spinal anterior horn cell excitability during motor imagery, healthy adult participants were recruited to measure the F-wave, an indicator of anterior horn cell excitability. F-waves were measured from participants at baseline, during motor imagery, and post-motor imagery. During motor imagery, participants imagined isometric thenar muscle activity at 50% maximum voluntary contraction for 5 min. F-waves were measured at 1, 3, and 5 min after beginning motor imagery and analysed for persistence and F/M amplitude ratio.

RESULTS

Persistence and F/M amplitude ratios at 1- and 3-min after motor imagery initiation were significantly greater than at baseline. The persistence and F/M amplitude ratio at 5-min after motor imagery initiation, however, was comparable to baseline levels.

CONCLUSION

Therefore, 1 to 3 min of motor imagery is likely sufficient to facilitate the excitability of spinal anterior horn cells.

Effect of the combination of motor imagery and electrical stimulation on upper extremity motor function in patients with chronic stroke: preliminary results

Background

The combination of motor imagery (MI) and afferent input with electrical stimulation (ES) enhances the excitability of the corticospinal tract compared with motor imagery alone or electrical stimulation alone. However, its therapeutic effect is unknown in patients with hemiparetic stroke. We performed a preliminary examination of the therapeutic effects of MI + ES on upper extremity (UE) motor function in patients with chronic stroke.

Methods

A total of 10 patients with chronic stroke demonstrating severe hemiparesis participated. The imagined task was extension of the affected finger. Peripheral nerve electrical stimulation was applied to the radial nerve at the spiral groove. MI + ES intervention was conducted for 10 days. UE motor function as assessed with the Fugl-Meyer assessment UE motor score (FMA-UE), the amount of the affected UE use in daily life as assessed with a Motor Activity Log (MAL-AOU), and the degree of hypertonia in flexor muscles as assessed with the Modified Ashworth Scale (MAS) were evaluated before and after intervention. To assess the change in spinal neural circuits, reciprocal inhibition between forearm extensor and flexor muscles with the H reflex conditioning-test paradigm at interstimulus intervals (ISIs) of 0, 20, and 100 ms were measured before and after intervention.

Results

UE motor function, the amount of the affected UE use, and muscle hypertonia in flexor muscles were significantly improved after MI + ES intervention (FMA-UE: p < 0.01, MAL-AOU: p < 0.01, MAS: p = 0.02). Neurophysiologically, the intervention induced restoration of reciprocal inhibition from the forearm extensor to the flexor muscles (ISI at 0 ms: p = 0.03, ISI at 20 ms: p = 0.03, ISI at 100 ms: p = 0.01).

Conclusion

MI + ES intervention was effective for improving UE motor function in patients with severe paralysis.

Imagery of movements immediately following performance allows learning of motor skills that interfere

Motor imagery, that is the mental rehearsal of a motor skill, can lead to improvements when performing the same skill. Here we show a powerful and complementary role, in which motor imagery of different movements after actually performing a skill allows learning that is not possible without imagery. We leverage a well-studied motor learning task in which subjects reach in the presence of a dynamic (force-field) perturbation. When two opposing perturbations are presented alternately for the same physical movement, there is substantial interference, preventing any learning. However, when the same physical movement is associated with follow-through movements that differ for each perturbation, both skills can be learned. Here we show that when subjects perform the skill and only imagine the follow-through, substantial learning occurs. In contrast, without such motor imagery there was no learning. Therefore, motor imagery can have a profound effect on skill acquisition even when the imagery is not of the skill itself. Our results suggest that motor imagery may evoke different neural states for the same physical state, thereby enhancing learning.

Muscle-selective disinhibition of corticomotor representations using a motor imagery-based brain-computer interface

Bridging between brain activity and machine control, brain-computer interface (BCI) can be employed to activate distributed neural circuits implicated in a specific aspect of motor control. Using a motor imagery-based BCI paradigm, we previously found a disinhibition within the primary motor cortex contralateral to the imagined movement, as evidenced by event-related desynchronization (ERD) of oscillatory cortical activity. Yet it is unclear whether this BCI approach does selectively facilitate corticomotor representations targeted by the imagery. To address this question, we used brain state-dependent transcranial magnetic stimulation while participants performed kinesthetic motor imagery of wrist movements with their right hand and received online visual feedback of the ERD. Single and paired-pulse magnetic stimulation were given to the left primary motor cortex at a low or high level of ERD to assess intracortical excitability. While intracortical facilitation showed no modulation by ERD, short-latency intracortical inhibition was reduced the higher the ERD. Intracortical disinhibition was only found in the agonist muscle targeted by motor imagery at high ERD level, but not in the antagonist muscle. Single pulse motor-evoked potential was also increased the higher the ERD. However, at high ERD level, this facilitatory effect on overall corticospinal excitability was not selective to the agonist muscle. Analogous results were found in two independent experiments, in which participants either performed kinesthetic motor imagery of wrist extension or flexion. Our results showed that motor imagery-based BCI can selectively disinhibit the corticomotor output to the agonist muscle, enabling effector-specific training in patients with motor paralysis.

Effects of Sensorimotor Rhythm Modulation on the Human Flexor Carpi Radialis H-Reflex

People can learn over training sessions to increase or decrease sensorimotor rhythms (SMRs) in the electroencephalogram (EEG). Activity-dependent brain plasticity is thought to guide spinal plasticity during motor skill learning; thus, SMR training may affect spinal reflexes and thereby influence motor control. To test this hypothesis, we investigated the effects of learned mu (8–13 Hz) SMR modulation on the flexor carpi radialis (FCR) H-reflex in 6 subjects with no known neurological conditions and 2 subjects with chronic incomplete spinal cord injury (SCI). All subjects had learned and practiced over more than 10 < 30-min training sessions to increase (SMR-up trials) and decrease (SMR-down trials) mu-rhythm amplitude over the hand/arm area of left sensorimotor cortex with ≥80% accuracy. Right FCR H-reflexes were elicited at random times during SMR-up and SMR-down trials, and in between trials. SMR modulation affected H-reflex size. In all the neurologically normal subjects, the H-reflex was significantly larger [116% ± 6 (mean ± SE)] during SMR-up trials than between trials, and significantly smaller (92% ± 1) during SMR-down trials than between trials (p < 0.05 for both, paired t-test). One subject with SCI showed similar H-reflex size dependence (high for SMR-up trials, low for SMR-down trials): the other subject with SCI showed no dependence. These results support the hypothesis that SMR modulation has predictable effects on spinal reflex excitability in people who are neurologically normal; they also suggest that it might be used to enhance therapies that seek to improve functional recovery in some individuals with SCI or other CNS disorders.

Visual Attention Affects the Amplitude of the Transcranial Magnetic Stimulation-associated Motor-evoked Potential: A Preliminary Study With Clinical Utility

BACKGROUND

The transcranial magnetic stimulation (TMS)-elicited motor-evoked potential (MEP) is a valuable measure for clinical evaluations of various neurological disorders and is used to determine resting motor threshold for repetitive TMS dosing. Although MEP amplitude is primarily associated with motor system function, there is evidence that nonmotor factors may also influence amplitude. This experiment tested the hypotheses that manipulation of 2 factors (visual attention, cognitive regulation) in human participants would significantly affect MEP amplitude.

METHODS

Blocks of MEPs were recorded from the dominant right hand as participants (N=20) were instructed to shift their visual attention (toward and away from the hand) and cognitively regulate the MEPs (rest, attenuate MEP amplitude, potentiate MEP amplitude) using their thoughts (6 blocks, 20 pulses/block, randomized, 110% resting motor threshold).

RESULTS

MEP amplitude was significantly affected by the direction of visual attention; looking away from the hand led to higher amplitudes (P=0.003). The relationship with cognitive regulation was nonsignificant.

CONCLUSIONS

The significant effect of visual attention on MEP suggests that this should be a standardized parameter in clinical and research studies. These data underscore the importance of rigorous reporting of methods and use of standardized practices for MEP acquisition and TMS dosing to ensure consistent clinical measurement and treatment.

Change in Reciprocal Inhibition of the Forearm with Motor Imagery among Patients with Chronic Stroke

We investigated cortically mediated changes in reciprocal inhibition (RI) following motor imagery (MI) in short- and long(er)-term periods. The goals of this study were (1) to describe RI during MI in patients with chronic stroke and (2) to examine the change in RI after MI-based brain-machine interface (BMI) training. Twenty-four chronic stroke patients participated in study 1. All patients imagined wrist extension on the affected side. RI from the extensor carpi radialis to the flexor carpi radialis (FCR) was assessed using a FCR H reflex conditioning-test paradigm. We calculated the "MI effect score on RI" (RI value during MI divided by that at rest) and compared that score according to lesion location. RI during MI showed a significant enhancement compared with RI at rest. The MI effect score on RI in the subcortical lesion group was significantly greater than that in the cortical lesion group. Eleven stroke patients participated in study 2. All patients performed BMI training for 10 days. The MI effect score on RI at a 20 ms interstimulus interval was significantly increased after BMI compared with baseline. In conclusion, mental practice with MI may induce plastic change in spinal reciprocal inhibitory circuits in patients with stroke.

Modulation of corticospinal excitability during positive and negative motor imageries

We investigated corticospinal excitability during positive (execution) and negative (suppression) imageries for the right and left upper and lower limbs. In the Positive Imagery tasks, sixteen subjects were instructed to repeatedly imagine rotation of the index finger of the right or left hand, or the ankle of the right or left foot. In the Negative Imagery tasks, they were asked to imagine the suppression of movements for the index finger of the right or left hand, or the ankle of the right or left foot. A single-pulse transcranial magnetic stimulation was delivered over the left hand primary motor cortex, and motor evoked potentials (MEPs) were recorded from the right first dorsal interosseous (FDI) muscle under all conditions. The MEP amplitudes of the FDI were significantly larger in the Positive and Negative Imagery tasks than in the resting control task during motor imagery of the right hand, left hand, and left foot, but not during that of right foot. Our results indicate that imageries of suppressing hand and foot movements enhanced corticospinal excitability.

Dynamic Changes in Upper-Limb Corticospinal Excitability during a 'Pro-/Anti-saccade' Double-Choice Task

Under natural behavioral conditions, visually guided eye movements are linked to direction-specific modulations of cortico-spinal system (CSS) excitability in upper-limb muscles, even in absence of a manual response. These excitability changes have been shown to be compatible with a covert motor program encoding a manual movement toward the same target of the eyes. The aim of this study is to investigate whether this implicit oculo-manual coupling is enforced following every saccade execution or it depends on the behavioral context. Twenty-two healthy young adults participated in the study. Single-pulse transcranial magnetic stimulation was applied to the motor cortex at nine different time epochs during a double-choice eye task, in which the decision to execute a prosaccade or an antisaccade was made on the color of a peripheral visual cue. By analyzing the amplitude of the motor evoked potentials (MEP) in three distal muscles of the resting upper-limb, a facilitation peak of CSS excitability was found in two of them at 120 ms before the eyes begin to move. Furthermore, a long-lasting, generalized reduced corticomotor excitability develops following the eye response. Finally, a quite large modulation of MEP amplitude, depending on the direction of the saccade, is observed only in the first dorsal interosseous muscle, in a narrow time window at about 150 ms before the eye movement, irrespective of the type of the ocular response (pro-/anti-saccade). This change in CSS excitability is not tied up to the timing of the occurrence of the visual cue but, instead, appears to be tightly time-related to the saccade onset. Observed excitability changes differ in many respects from those previously reported with different behavioral paradigms. A main finding of our study is that the implicit coupling between eye and hand motor systems is contingent upon the particular motor set determined by the cognitive aspects of the performed oculomotor task. In particular, the direction-specific modulation in CSS excitability described in this study appears to be related to perceptual and decision-making processes rather than representing an implicit upper-limb motor program, coupled to the saccade execution.