Modulations in corticomotor excitability during passive upper-limb movement: is there a cortical influence?

Does 20 Hz Transcranial Alternating Current Stimulation over the Human Primary Motor Cortex Modulate Beta Rebound Following Voluntary Movement?

Beta frequency oscillations originating from the primary motor cortex increase in amplitude following the initiation of voluntary movement, a process termed beta rebound. The strength of beta rebound has been reported to predict the recovery of motor function following stroke, suggesting therapeutic applications of beta rebound modulation. The present study examined the effect of 20 Hz transcranial alternating current stimulation (tACS) on the beta rebound induced by self-paced voluntary movement. Electroencephalograms (EEGs) and electromyograms (EMGs) were recorded from 16 healthy adults during voluntary movements performed before and after active or sham tACS. There was no significant change in average beta rebound after active tACS. However, the beta rebound amplitude was significantly enhanced in a subset of participants, and the magnitude of the increase across all participants was negatively correlated with the difference between individual peak beta frequency and tACS frequency. Thus, matching the stimulus frequency of tACS with individual beta frequency may facilitate therapeutic enhancement for motor rehabilitation.

Effect of muscle length in a handgrip task on corticomotor excitability of extrinsic and intrinsic hand muscles under resting and submaximal contraction conditions

The neurophysiological mechanisms underlying muscle force control for different wrist postures still need to be better understood. To further elucidate these mechanisms, the present study aimed to investigate the effects of wrist posture on the corticospinal excitability by transcranial magnetic stimulation (TMS) of extrinsic (flexor [FCR] and extensor carpi radialis [ECR]) and intrinsic (flexor pollicis brevis (FPB)) muscles at rest and during a submaximal handgrip strength task. Fourteen subjects (24.06 ± 2.28 years) without neurological or motor disorders were included. We assessed how the wrist posture (neutral: 0°; flexed: +45°; extended: -45°) affects maximal handgrip strength (HGSmax ) and the motor evoked potentials (MEP) amplitudes during rest and active muscle contractions. HGSmax was higher at 0° (133%) than at -45° (93.6%; p < 0.001) and +45° (73.9%; p < 0.001). MEP amplitudes were higher for the FCR at +45° (83.6%) than at -45° (45.2%; p = 0.019) and at +45° (156%; p < 0.001) and 0° (146%; p = 0.014) than at -45° (106%) at rest and active condition, respectively. Regarding the ECR, the MEP amplitudes were higher at -45° (113%) than at +45° (60.8%; p < 0.001) and 0° (72.6%; p = 0.008), and at -45° (138%) than +45° (96.7%; p = 0.007) also at rest and active conditions, respectively. In contrast, the FPB did not reveal any difference among wrist postures and conditions. Although extrinsic and intrinsic hand muscles exhibit overlapping cortical representations and partially share the same innervation, they can be modulated differently depending on the biomechanical constraints.

Acupuncture Therapy on Patients with Flaccid Hemiplegia after Stroke: A Systematic Review and Meta-Analysis

Background

Acupuncture is a commonly used complementary treatment for flaccid hemiplegia caused by stroke, but evidences from previous randomized trials were inconclusive. The purpose of this study was to evaluate the efficacy and safety of acupuncture in a comprehensive synthesis.

Methods

We searched literature from eight databases from their inception to December 2020. We included randomized controlled trials of acupuncture for the treatment of flaccid hemiplegia following stroke. The meta-analysis was carried out using Review Manager 5.3 and Stata 16.0. The main indicator was the Fugl-Meyer Assessment scale. The modified Barthel Index scale, Quality Of Life Assessment scale, Mini-Mental State Examination scale, Berg Balance Scale, Neurological Deficit Assessment scale, and the treatment effective rate were used to measure the secondary indicators. Adverse events from individual studies were used to determine safety.

Results

Our search returned 7624 records, of which 27 studies involving a total of 1,293 patients fulfilled our inclusion criteria. To be noted, our results indicated that significant improvements in the scores of the primary indicator showed better clinical scores among the three groups with acupuncture than without acupuncture: acupuncture compared with rehabilitation, 13.53 (95% CI 11.65–14.41, P < 0.01); acupuncture plus rehabilitation compared with rehabilitation, 9.84 (95% CI 6.45–13.24, P < 0.01, I² = 98%); and acupuncture plus Western medicine therapy compared with Western medicine, 16.86 (95% CI 15.89–17.84, P < 0.01, I² = 38%), and the secondary indicators showed the same tendency.

Conclusion

Acupuncture was effective and safe in the patients with flaccid hemiplegia after stroke, although there was high heterogeneity between studies.

Corticospinal responses during passive shortening and lengthening of tibialis anterior and soleus in older compared to younger adults

NEW FINDINGS

What is the central question of this study? Are there age-related differences in corticospinal responses whilst passively changing muscle length? What is the main finding and its importance? In contrast to young, older adults exhibited no modulation of corticospinal excitability in tibialis anterior during passive ankle movement. These data show impaired sensorimotor response in older adults during length changes of tibialis anterior, thus contributing to our understanding of age-related changes in sensorimotor control.

ABSTRACT

Corticospinal responses have been shown to increase and decrease with passive muscle shortening and lengthening, respectively, as a result of changes in muscle spindle afferent feedback. The ageing sensory system is accompanied by a number of alterations that might influence the processing and integration of sensory information. Consequently, corticospinal excitability might be modulated differently whilst changing muscle length. In 10 older adults (66 ± 4 years), corticospinal responses (MEP/M_max ) were evoked in a static position, and during passive shortening and lengthening of soleus (SOL) and tibialis anterior (TA), and these data were compared to the re-analysed data pool of 18 younger adults (25 ± 4 years) published previously. Resting motor threshold was greater in SOL compared to TA (P < 0.001), but did not differ between young and older (P = 0.405). No differences were observed in MEP/M_max between the static position, passive shortening or lengthening in SOL (young: all 0.02 ± 0.01; older: 0.05 ± 0.04, 0.03 ± 0.02 and 0.04 ± 0.01, respectively; P = 0.298), and responses were not dependent on age (P = 0.090). Conversely, corticospinal responses in TA were modulated differently between the age groups (P = 0.002), with greater MEP/M_max during passive shortening (0.22 ± 0.12) compared to passive lengthening (0.13 ± 0.10) and static position (0.10 ± 0.05) in young (P < 0.001), but unchanged in older adults (0.19 ± 0.11, 0.22 ± 0.11 and 0.18 ± 0.07, respectively; P ≥ 0.867). The present experiment shows that length-dependent changes in corticospinal excitability in TA of the young are not evident in older adults. This suggests impaired sensorimotor response during muscle length changes in older age that might only be present in ankle flexors, but not extensors.

Corticospinal excitability of tibialis anterior and soleus differs during passive ankle movement

The purpose of this study was to assess corticospinal excitability of soleus (SOL) and tibialis anterior (TA) at a segmental level during passive ankle movement. Four experimental components were performed to assess the effects of passive ankle movement and muscle length on corticospinal excitability (MEP/M_max) at different muscle lengths, subcortical excitability at the level of lumbar spinal segments (LEP/M_max), intracortical inhibition (SICI) and facilitation (ICF), and H-reflex in SOL and TA. In addition, the degree of fascicle length changes between SOL and TA was assessed in a subpopulation during passive ankle movement. Fascicles shortened and lengthened with joint movement during passive shortening and lengthening of SOL and TA to a similar degree (p < 0.001). Resting motor threshold was greater in SOL compared to TA (p ≤ 0.014). MEP/M_max was facilitated in TA during passive shortening relative to the static position (p ≤ 0.023) and passive lengthening (p ≤ 0.001), but remained similar during passive ankle movement in SOL (p ≥ 0.497), regardless of muscle length at the point of stimulus (p = 0.922). LEP/M_max (SOL: p = 0.075, TA: p = 0.071), SICI (SOL: p = 0.427, TA: p = 0.540), and ICF (SOL: p = 0.177, TA: p = 0.777) remained similar during passive ankle movement. H-reflex was not different across conditions in TA (p = 0.258), but was reduced during passive lengthening compared to shortening in SOL (p = 0.048). These results suggest a differential modulation of corticospinal excitability between plantar and dorsiflexors during passive movement. The corticospinal behaviour observed might be mediated by an increase in corticospinal drive as a result of reduced afferent input during muscle shortening and appears to be flexor-biased.

Effects of Assist-As-Needed Upper Extremity Robotic Therapy after Incomplete Spinal Cord Injury: A Parallel-Group Controlled Trial

BACKGROUND

Robotic rehabilitation of the upper limb following neurological injury has been supported through several large clinical studies for individuals with chronic stroke. The application of robotic rehabilitation to the treatment of other neurological injuries is less developed, despite indications that strategies successful for restoration of motor capability following stroke may benefit individuals with incomplete spinal cord injury (SCI) as well. Although recent studies suggest that robot-aided rehabilitation might be beneficial after incomplete SCI, it is still unclear what type of robot-aided intervention contributes to motor recovery.

METHODS

We developed a novel assist-as-needed (AAN) robotic controller to adjust challenge and robotic assistance continuously during rehabilitation therapy delivered via an upper extremity exoskeleton, the MAHI Exo-II, to train independent elbow and wrist joint movements. We further enrolled seventeen patients with incomplete spinal cord injury (AIS C and D levels) in a parallel-group balanced controlled trial to test the efficacy of the AAN controller, compared to a subject-triggered (ST) controller that does not adjust assistance or challenge levels continuously during therapy. The conducted study is a stage two, development-of-concept pilot study.

RESULTS

We validated the AAN controller in its capability of modulating assistance and challenge during therapy via analysis of longitudinal robotic metrics. For the selected primary outcome measure, the pre-post difference in ARAT score, no statistically significant change was measured in either group of subjects. Ancillary analysis of secondary outcome measures obtained via robotic testing indicates gradual improvement in movement quality during the therapy program in both groups, with the AAN controller affording greater increases in movement quality over the ST controller.

CONCLUSION

The present study demonstrates feasibility of subject-adaptive robotic therapy after incomplete spinal cord injury, but does not demonstrate gains in arm function occurring as a result of the robot-assisted rehabilitation program, nor differential gains obtained as a result of the developed AAN controller. Further research is warranted to better quantify the recovery potential provided by AAN control strategies for robotic rehabilitation of the upper limb following incomplete SCI. ClinicalTrials.gov registration number: NCT02803255.

Continuous passive motion improves shoulder joint integrity following stroke

Objective: In a pilot study of patients with a first stroke and hemiparesis, we sought to determine whether treatment of the upper limb with continuous passive motion (CPM) that was device delivered would alter impairment, disability or the associated adverse symptoms of shoulder joint instability, pain and tone.

Design: Patients were randomly assigned to receive daily CPM treatments or participate in self-range of motion groups under the supervision of an occupational therapist. All patients received standard daily poststroke therapy for 3.5 h per day. A blinded evaluator at admission and discharge assessed patients using standardized scales of impairment, disability and adverse symptoms.

Setting: Specialized stroke unit of an acute rehabilitation hospital.

Subjects: Two hundred and eighty consecutive patients were screened and 35 of these with a first unilateral stroke, 139-6 days following the acute event, provided informed consent and were randomly assigned to CPM treatment or supervised group self-range exercise.

Main measures: Thirty-two completed the study and were evaluated using standardized measures for motor impairment (Fugl-Meyer, Motor Status Scale and Medical Research Council Motor Power), adverse symptoms (gleno-humeral stability, pain and tone), and disability (Functional Independence Measure).

Results: CPM-treated patients demonstrated positive trends towards improved shoulder joint stability (p =0.06, confidence interval -0.03, 2.3) when compared with patients performing therapist-supervised self-range of motion. There were no significant differences in motor impairment, disability, pain or tone.

Conclusions: Device-delivered continuous passive range of motion may offer an enhanced benefit for some adverse symptom reduction in the hemiplegic arm after stroke over traditional self-range of motion exercise.

Bringing transcranial mapping into shape: Sulcus-aligned mapping captures motor somatotopy in human primary motor hand area

Motor representations express some degree of somatotopy in human primary motor hand area (M1HAND), but within-M1HAND corticomotor somatotopy has been difficult to study with transcranial magnetic stimulation (TMS). Here we introduce a "linear" TMS mapping approach based on the individual shape of the central sulcus to obtain mediolateral corticomotor excitability profiles of the abductor digiti minimi (ADM) and first dorsal interosseus (FDI) muscles. In thirteen young volunteers, we used stereotactic neuronavigation to stimulate the right M1HAND with a small eight-shaped coil at 120% of FDI resting motor threshold. We pseudorandomly stimulated six targets located on a straight mediolateral line corresponding to the overall orientation of the central sulcus with a fixed coil orientation of 45° to the mid-sagittal line (STRAIGHT-450FIX) or seven targets in the posterior part of the crown of the central sulcus following the bending of the central sulcus (CURVED). CURVED mapping employed a fixed (CURVED-450FIX) or flexible coil orientation producing always a current perpendicular to the sulcal wall (CURVED-900FLEX). During relaxation, CURVED but not STRAIGHT mapping revealed distinct corticomotor excitability peaks in M1HAND with the excitability maximum of ADM located medially to the FDI maximum. This mediolateral somatotopy was still present during tonic contraction of the ADM or FDI. During ADM contraction, cross-correlation between the spatial excitability profiles of ADM and FDI was lowest for CURVED-900FLEX. Together, the results show that within-M1HAND somatotopy can be readily probed with linear TMS mapping aligned to the sulcal shape. Sulcus-aligned linear mapping will benefit non-invasive studies of representational plasticity in human M1HAND.

Carryover effects of cyclical stretching of the digits on hand function in stroke survivors

OBJECTIVE

To investigate the longevity and cumulative impact of multiple sessions of passive, cyclical stretching of the digits on hand function in subacute stroke survivors.

DESIGN

Before-after trial with intervention repeated on 3 consecutive days.

SETTING

Research laboratory.

PARTICIPANTS

Individuals (N=27) with moderate to severe hand impairment, 2 to 6 months (subacute, n=12) and >7 months (chronic, n=15) poststroke.

INTERVENTIONS

Subjects wore an actuated glove orthosis that cyclically moved their fingers and thumb from a relaxed/flexed posture into neutral extension for 30 minutes on 3 consecutive days.

MAIN OUTCOME MEASURES

Three hand-specific tasks from the Graded Wolf Motor Function Test, Box and Block Test (BBT), grip strength, and lateral pinch strength. Recordings were taken before stretching and at 3 time points, each separated by 30 minutes after completion of stretching on each day.

RESULTS

Significant improvement was observed immediately after the stretching for both groups. Improvements in the subacute group were largely maintained up to 1 hour poststretching, with significant carryover from day to day for some outcomes measures such as the BBT (P=.006) and grip strength (P=.012). In contrast, improvements after stretching for the chronic group were transient, with the changes largely dissipating over time and no significant cumulative effect across days.

CONCLUSIONS

Cyclical stretching of the digits had a lasting and reinforcing effect on improving hand motor control for subacute stroke survivors. Incorporation of cyclical stretching before active hand therapy may prove to be a beneficial treatment for stroke survivors, especially during the subacute phase of recovery.

Corticomotor excitability changes seen in the resting forearm during contralateral rhythmical movement and force manipulations: a TMS study

The aim of this study was to examine changes in corticomotor excitability to a resting wrist extensor muscle during contralateral rhythmical isotonic and static isometric wrist contractions (flexion/extension) at different loads and positions, using transcranial magnetic stimulation (TMS). TMS-induced motor-evoked potentials (MEPs) were recorded from the relaxed right extensor carpi radialis (ECR) and flexor carpi radialis (FCR) respectively, while the left arm underwent unimanual manipulations. Rhythmical isotonic (0.5 Hz) flexion and extension movements of the left wrist under 3 load conditions (no, low and high force) and a frequency matched passive movement condition were collected, along with isometric flexion/extension contractions in each position (low and high force). TMS was delivered at eight positions (4 in the flexion phase and 4 in the extension phase) during the continuous movement conditions and each of these positions was sampled with isometric contraction. The potentials evoked by TMS in right ECR were potentiated when the left ECR was engaged, independent of position within that phase of contraction or contraction type (isotonic and isometric). Motor cortical excitability of the resting right ECR increased as load demands increased to the left wrist. Passive rhythmical movement did not influence excitability to the resting ECR implying that voluntary motor drive is required. Our findings indicated that the increase in corticomotor drive during both rhythmic isotonic and static isometric contractions of the opposite limb is likely mediated by interhemispheric interactions between cortical motor areas. Improving our understanding of these cortical networks can be useful in future methods to enhance neuroplasticity through neurorehabilitation methods.

Real-time changes in corticospinal excitability during voluntary contraction with concurrent electrical stimulation

While previous studies have assessed changes in corticospinal excitability following voluntary contraction coupled with electrical stimulation (ES), we sought to examine, for the first time in the field, real-time changes in corticospinal excitability. We monitored motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation and recorded the MEPs using a mechanomyogram, which is less susceptible to electrical artifacts. We assessed the MEPs at each level of muscle contraction of wrist flexion (0%, 5%, or 20% of maximum voluntary contraction) during voluntary wrist flexion (flexor carpi radialis (FCR) voluntary contraction), either with or without simultaneous low-frequency (10 Hz) ES of the median nerve that innervates the FCR. The stimulus intensity corresponded to 1.2× perception threshold. In the FCR, voluntary contraction with median nerve stimulation significantly increased corticospinal excitability compared with FCR voluntary contraction without median nerve stimulation (p<0.01). In addition, corticospinal excitability was significantly modulated by the level of FCR voluntary contraction. In contrast, in the extensor carpi radialis (ECR), FCR voluntary contraction with median nerve stimulation significantly decreased corticospinal excitability compared with FCR voluntary contraction without median nerve stimulation (p<0.05). Thus, median nerve stimulation during FCR voluntary contraction induces reciprocal changes in cortical excitability in agonist and antagonist muscles. Finally we also showed that even mental imagery of FCR voluntary contraction with median nerve stimulation induced the same reciprocal changes in cortical excitability in agonist and antagonist muscles. Our results support the use of voluntary contraction coupled with ES in neurorehabilitation therapy for patients.

Mirror symmetric bimanual movement priming can increase corticomotor excitability and enhance motor learning

Repetitive mirror symmetric bilateral upper limb may be a suitable priming technique for upper limb rehabilitation after stroke. Here we demonstrate neurophysiological and behavioural after-effects in healthy participants after priming with 20 minutes of repetitive active-passive bimanual wrist flexion and extension in a mirror symmetric pattern with respect to the body midline (MIR) compared to an control priming condition with alternating flexion-extension (ALT). Transcranial magnetic stimulation (TMS) indicated that corticomotor excitability (CME) of the passive hemisphere remained elevated compared to baseline for at least 30 minutes after MIR but not ALT, evidenced by an increase in the size of motor evoked potentials in ECR and FCR. Short and long-latency intracortical inhibition (SICI, LICI), short afferent inhibition (SAI) and interhemispheric inhibition (IHI) were also examined using pairs of stimuli. LICI differed between patterns, with less LICI after MIR compared with ALT, and an effect of pattern on IHI, with reduced IHI in passive FCR 15 minutes after MIR compared with ALT and baseline. There was no effect of pattern on SAI or FCR H-reflex. Similarly, SICI remained unchanged after 20 minutes of MIR. We then had participants complete a timed manual dexterity motor learning task with the passive hand during, immediately after, and 24 hours after MIR or control priming. The rate of task completion was faster with MIR priming compared to control conditions. Finally, ECR and FCR MEPs were examined within a pre-movement facilitation paradigm of wrist extension before and after MIR. ECR, but not FCR, MEPs were consistently facilitated before and after MIR, demonstrating no degradation of selective muscle activation. In summary, mirror symmetric active-passive bimanual movement increases CME and can enhance motor learning without degradation of muscle selectivity. These findings rationalise the use of mirror symmetric bimanual movement as a priming modality in post-stroke upper limb rehabilitation.

Excitability changes in the ipsilateral primary motor cortex during rhythmic contraction of finger muscles

The aim of this study was to determine whether the excitatory ipsilateral primary motor cortex (ipsi-M1) is affected by changes in the frequency of rhythmic voluntary contraction of the left first dorsal interosseous (FDI) induced by repetitive abduction of the left index-finger. Transcranial magnetic stimulations were delivered to the left M1 during repetitive left index-finger abduction at 1, 2, and 3Hz, and motor evoked potentials (MEPs) were simultaneously evoked in the resting right (Rt)-FDI, Rt-abductor pollicis brevis, and Rt-abductor digiti minimi. The stimulus-response (S-R) curve of the MEP at each frequency was recorded. In addition, F-waves were recorded from the Rt-FDI during these rhythmic contraction tasks in order to examine the changes in spinal motoneuron excitability. MEPs were markedly increased under the 3Hz conditions compared with the other conditions. However, F-waves were hardly changed under these conditions. The S-R curve of the MEP induced under the 3Hz conditions was significantly steeper than the curves produced under other conditions. Our results indicate that the excitability of ipsi-M1 is affected by the frequency of rhythmic voluntary contraction of unilateral finger movement, which may be caused by neural inputs delivered via a transcallosal pathway.

Corticomotor excitability of wrist flexor and extensor muscles during active and passive movement

The excitability of the corticospinal projection to upper and lower limbs is constantly modulated during voluntary and passive movement; however a direct comparison during a comparable movement has not been reported. In the present study we used transcranial magnetic stimulation (TMS) to compare corticomotor excitability to the extensor and flexor carpi radialis (ECR/FCR) muscles of the forearm during voluntary rhythmic wrist movement (through 45 degrees of range), during a matched (for range and rhythm) passive movement of the wrist, and while the wrist was stationary (in mid-range). TMS was delivered when the wrist was in the neutral position. With passive and active movement, and for both FCR and ECR, corticomotor excitability was reduced during lengthening relative to shortening phases of movement. With active movement, this pattern was maintained and superimposed on an overall increase in excitability to both muscles that was greater for the ECR. The results favor a common pattern of excitability changes shared by extensor and flexor muscles as they undergo lengthening and shortening, which may be mediated by afferent input during both passive and active movement. This is combined with an overall increase in excitability associated with active movement that is greater for extensor muscles perhaps due to differences in the strength of the corticomotor projection to these muscles.

INFLUENCE OF MIRROR THERAPY ON HUMAN MOTOR CORTEX

This article investigates whether or not mirror therapy alters the neural mechanisms in human motor cortex. Six healthy volunteers participated. The study investigated the effects of three main factors of mirror therapy (observation of hand movements in a mirror, motor imagery of an assumed affected hand, and assistance in exercising the assumed affected hand) on excitability changes in the human motor cortex to clarify the contribution of each factor. The increase in motor-evoked potential (MEP) amplitudes during motor imagery tended to be larger with a mirror than without one. Moreover, MEP amplitudes increased greatly when movements were assisted. Watching the movement of one hand in a mirror makes it easier to move the other hand in the same way. Moreover, the increase in MEP amplitudes is related to the synergic effects of afferent information and motor imagery.

Facilitation of corticospinal excitability in the tibialis anterior muscle during robot-assisted passive stepping in humans

Although phasic modulation of the corticospinal tract excitability to the lower limb muscles has been observed during normal walking, it is unclear to what extent afferent information induced by walking is related to the modulation. The purpose of this study was to test the corticospinal excitability to the lower limb muscles by using transcranial magnetic stimulation (TMS) and transcranial electrical stimulation of the motor cortex while 13 healthy subjects passively stepped in a robotic driven-gait orthosis. Specifically, to investigate the effect of load-related afferent inputs on the corticospinal excitability during passive stepping, motor evoked potentials (MEPs) in response to the stimulation were compared between two passive stepping conditions: 40% body weight unloading on a treadmill (ground stepping) and 100% body weight unloading in the air (air stepping). In the rectus femoris, biceps femoris and tibialis anterior (TA) muscles, electromyographic activity was not observed throughout the step cycle in either stepping condition. However, the TMS-evoked MEPs of the TA muscle at the early- and late-swing phases as well as at the early-stance phase during ground stepping were significantly larger than those observed during air stepping. The modulation pattern of the transcranial electrical stimulation-evoked MEPs was similar to that of the TMS-evoked MEPs. These results suggest that corticospinal excitability to the TA is facilitated by load-related afferent inputs. Thus, these results might be consistent with the notion that load-related afferent inputs play a significant role during locomotor training for gait disorders.

Motor strategies and excitability changes of human hand motor area are dependent on different voluntary drives

The present study examined whether there were different voluntary drives between intended and non-intended muscle contractions. In experiment 1, during intended and non-intended muscle contractions, electromyograms (EMGs) were recorded from the first dorsal interosseous (FDI) and extensor carpi radialis (ECR) muscles when force levels were varied from 10% to 50% maximal voluntary contraction (MVC) in 10% MVC steps. In experiment 2, using transcranial magnetic stimulation, motor-evoked potentials (MEPs) were recorded from the FDI muscle when EMGs were varied from 10% to 40% EMGmax (EMG activities during MVC) in 10% EMGmax steps during intended and non-intended muscle contractions. In experiment 3, at 10% MVC force level MEPs were recorded before and after practice. The results showed that, in the FDI muscle, EMGs during intended muscle contractions were larger than those during non-intended ones at higher force levels (30-50% MVC). In the ECR muscle, reverse results were observed. At comparable EMG levels of the FDI muscle MEPs were the same during intended and non-intended muscle contractions. After practice, MEPs during intended muscle contraction became larger than those during non-intended at 10% MVC force level, while EMGs were the same between two muscle contractions. It is concluded that motor strategies and excitability changes of hand motor area are different during intended and non-intended muscle contractions, and these differences are due to the different voluntary drives of intended and non-intended. The present findings may contribute to the understanding of rehabilitation for patients suffering from damages of the central motor system.

Robotics and other devices in the treatment of patients recovering from stroke

Stroke is the leading cause of permanent disability in the United States despite advances in prevention and novel interventional treatments. Randomized controlled studies have demonstrated the effectiveness of specialized post-stroke rehabilitation units, but administrative orders have severely limited the length of stay, so novel approaches to the treatment of recovery need to be tested in outpatients. Although the mechanisms of stroke recovery depend on multiple factors, a number of techniques that concentrate on enhanced exercise of the paralyzed limb have demonstrated effectiveness in reducing the motor impairment. For example, interactive robotic devices are new tools for therapists to deliver enhanced sensorimotor training for the paralyzed upper limb, which can potentially improve patient outcome and increase patient productivity. New data support the idea that for some post-stroke patients and for some aspects of training-induced recovery, timing of the training may be less important than the quality and intensity of the training. The positive outcome that resulted in the interactive robotic trials contrasts with the failure to find a beneficial result in trials that used a noninteractive device that delivered continuous passive motion only. New pilot data from novel devices to move the wrist demonstrate benefit and suggest that successive improvement of the function of the arm progressing to the distal muscles may eventually lead to significant disability reduction. These data from robotic trials continue to contribute to the emerging scientific basis of neuro-rehabilitation.

Neural pathways mediating bilateral interactions between the upper limbs

The ease with which we perform tasks such as opening the lid of a jar, in which the two hands execute quite different actions, belies the fact that there is a strong tendency for the movements of the upper limbs to be drawn systematically towards one another. Mirror movements, involuntary contractions during intended unilateral engagement of the opposite limb, are considered pathological, as they occur in association with specific disorders of the CNS. Yet they are also observed frequently in normally developing children, and motor irradiation, an increase in the excitability of the (opposite) homologous motor pathways when unimanual movements are performed, is a robust feature of the mature motor system. The systematic nature of the interactions that occur between the upper limbs has also given rise to the expectation that functional improvements in the control of a paretic limb may occur when movements are performed in a bimanual context. In spite of the ubiquitous nature of these phenomena, there is remarkably little consensus concerning the neural basis of their mediation. In the present review, consideration is given to the putative roles of uncrossed corticofugal fibers, branched bilateral corticomotoroneuronal projections, and segmental networks. The potential for bilateral interactions to occur in various brain regions including the primary motor cortex, the supplementary motor area, non-primary motor areas, the basal ganglia, and the cerebellum is also explored. This information may provide principled bases upon which to evaluate and develop task and deficit-specific programs of movement rehabilitation and therapy.

Amplitude of muscle stretch modulates corticomotor gain during passive movement

Previous studies have shown that the excitability of corticomotor projections to forearm muscles exhibit phasic modulation during passive movement (flexion-extension) about the wrist joint. We examined the stimulus-response properties of flexor carpi radialis (FCR) and extensor carpi radialis (ECR) to transcranial magnetic stimulation (TMS) applied over the contralateral motor cortex while the wrist was moved passively at two different sinusoidal frequency-amplitude relationships. Movement velocity (and therefore, the rate of change in muscle length) at the time of stimulation was held constant. Motor evoked potential (MEP) amplitudes were facilitated during passive muscle shortening and suppressed during passive muscle lengthening with suppression being more evident at higher stimulation intensities. For both FCR and ECR, during the shortening phase, responses were facilitated during the large amplitude movement relative to the small amplitude movement. It is suggested that the altered gain may be related to the thixotropic properties of muscle.

Robotics and other devices in the treatment of patients recovering from stroke

Stroke is the leading cause of permanent disability in the United States despite advances in prevention and novel interventional treatments. Randomized controlled studies have demonstrated the effectiveness of specialized post-stroke rehabilitation units, but administrative orders have severely limited the length of stay, so novel approaches to the treatment of recovery need to be tested in outpatients. Although the mechanisms of stroke recovery depend on multiple factors, a number of techniques that concentrate on enhanced exercise of the paralyzed limb have demonstrated effectiveness in reducing the motor impairment. For example, interactive robotic devices are new tools for therapists to deliver enhanced sensorimotor training for the paralyzed upper limb, which can potentially improve patient outcome and increase their productivity. New data support the idea that for some post-stroke patients and for some aspects of training-induced recovery, timing of the training may be less important than the quality and intensity of the training. The positive outcome that resulted in the interactive robotic trials contrasts with the failure to find a beneficial result in trials that used a noninteractive device that delivered continuous passive motion only. New pilot data from novel devices to move the wrist demonstrate benefit and suggest that successive improvement of the function of the arm progressing to the distal muscles may eventually lead to significant disability reduction. These data from robotic trials continue to contribute to the emerging scientific basis of neuro-rehabilitation.

The effect of postural stability and spatial orientation of the upper limbs on interlimb coordination

It has recently been reported that the spatial orientation of two moving limbs has a determining influence on the relative accuracy and stability of coordination patterns. The purpose of the present experiments was to test perceptual and neuromuscular explanations of these spatial orientation effects. Experiment 1 was an initial test of the hypotheses and an extension of a previous study [Lee et al. (2002) Exp Brain Res 146:205-212] that required participants to coordinate inphase and antiphase movement patterns in four spatial orientations: two symmetric orientations (90 degrees and 180 degrees separation between the limbs) and two asymmetric orientations (90 degrees and 135 degrees separation between the limbs). Results of Experiment 1 suggest that the symmetry of movement may be a key factor influencing spatial orientation effects observed during interlimb coordination. In Experiment 2, participants again performed inphase and antiphase movement patterns in symmetric and asymmetric spatial orientations. However, one-half of the participants in Experiment 2 were provided with mechanical constraints during the performance of the desired coordination patterns. The mechanical constraints provided postural support but did not influence the visual experience. Results showed that the addition of the postural support improved performance. These findings suggest that neuromuscular, and perhaps biomechanical, constraints contribute more to the influence of spatial orientation than visual-perceptual constraints.

Depression of diaphragm motor cortex excitability during mechanical ventilation

The effect of mechanical ventilation on the diaphragm motor cortex remains unknown. We assessed the effect of mechanical ventilation on diaphragm motor cortex excitability by measuring the costal and crural diaphragm motor-evoked potential (MEP) elicited by single and paired transcranial magnetic stimulation. In six healthy subjects, MEP recruitment curves of the costal and crural diaphragms were assessed at relaxed end expiration during spontaneous breathing [baseline tidal volume (Vtbaseline)] and isocapnic volume cycled ventilation delivered noninvasively (NIV) at three different levels of tidal volume (Vtbaseline, Vtbaseline + 5 ml/kg liters, and Vtbaseline + 10 ml/kg liters). The costal and crural diaphragm response to peripheral stimulation of the right phrenic nerve was not reduced by NIV. NIV reduced the costal and crural MEP amplitude during NIV ( P < 0.0001) with the maximal reduction at Vtbaseline + 5 ml/kg. Response to paired TMS showed that NIV (Vtbaseline + 5 ml/kg) significantly increased the sensitivity of the cortical motoneurons to facilitatory (>9 ms) interstimulus intervals ( P = 0.002), suggesting that the diaphragm MEP amplitude depression during NIV is related to neuromechanical inhibition at the level of motor cortex. Our results demonstrate that mechanical ventilation directly inhibits central projections to the diaphragm.

The effects of repetitive proprioceptive stimulation on corticomotor representation in intact and hemiplegic individuals

OBJECTIVE

To determine the effects of a passive wrist movement intervention on cortical representation of forearm musculature.

METHODS

Transcranial magnetic stimulation was used to map cortical representation of a forearm flexor muscle in healthy individuals and in individuals following stroke before and immediately after a 30 min session of passive wrist movement.

RESULTS

In the healthy individuals, no changes in map area or map centre of gravity were noted after the intervention; however, map volume increased significantly across all subjects. In the stroke patient group there were no significant changes in any parameters following the intervention.

CONCLUSIONS

It is speculated that the enlargement in map volume following the passive movement intervention arose through a heightened synaptic efficacy of the corticospinal pathway in response to the increase in afferent information. Short-term proprioceptive stimulation can induce alterations in corticomotor excitability in the target musculature.

SIGNIFICANCE

These findings provide a potential neural substrate to account for alterations in motor and sensory function in stroke patients in response to long-term passive movement interventions.