Reciprocal change of motor-evoked potentials preceding voluntary movement in humans

Reciprocal change of motor-evoked potentials (MEPs) recorded from the agonist and antagonist muscles of the forearm was studied in 10 normal subjects in whom transcranial magnetic stimulation (TMS) was applied to the hand motor area before voluntary wrist movements. MEP recorded from the agonist muscles, that is, radial extensor muscles for wrist extension and ulnar flexor muscle for wrist flexion, were gradually facilitated with shortening of the interval between the magnetic stimulation and the voluntary muscle contraction. In contrast, MEP recorded from the antagonist muscles, that is, ulnar flexor muscle for wrist extension and radial extensor muscles for wrist flexion, were gradually suppressed as the interval shortened. The reciprocal change of MEP was recognized when TMS was applied within 60 ms prior to the voluntary movements. The present data confirmed that reciprocal change of MEP was recognized before voluntary movements; they further suggest that cortically originated reciprocal control of the corticospinal pathway may exist and that it may be generated just before the voluntary movement. © 1996 John Wiley & Sons, Inc.     

Temporal changes of pyramidal tract activities after decision of movement: a study using transcranial magnetic stimulation of the motor cortex in humans

To elucidate the effects of the decision to move on the pyramidal tract in humans, we examined the changes in the motor evoked potentials (MEP) of the forearm muscles following transcranial magnetic cortical stimulation (TMS) of the hand area during a go/no-go hand-movement task in 10 normal subjects. The subjects performed an extension of the right wrist according to the go, no-go and control signals, one of which was randomly presented on a TV. A single TMS was applied to the primary hand motor area in the left hemisphere 0–300 ms after each signal. The MEPs recorded from the wrist extensor and flexor muscles changed in amplitude after both go and no-go signals. In comparison with the control, the MEPs were significantly facilitated in the agonistic muscles (wrist extensor muscles) and attenuated in the antagonistic muscles (wrist flexor muscles), at the latencies of 100–200 ms after the go signal (P<0.02). In contrast, the MEPs of both the extensor and flexor muscles were significantly attenuated during the period of 100–200 ms after the no-go signal (P<0.001). We speculate that there is strong inhibition on the pyramidal tract after the no-go signal and that the inhibitory effect is non-specific to the target muscles. This inhibition differs from the reciprocal inhibition of the MEP observed in antagonistic muscles after the go signal, and it is probably related to the movement decision originating in the prefrontal cortex.     

Subthreshold corticospinal control of anticipatory actions in humans

Previous findings suggest that, by influencing the subthreshold state of motoneurons, the corticospinal pathways can set and reset the threshold position at which wrist muscle recruitment begins. Here we assumed that the corticospinal system can change the threshold position in a similar way before anticipated perturbation to pre-determine an appropriate emerging response to it. We first analyzed motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) applied to the wrist area of motor cortex before unloading of preloaded wrist flexors, i.e. before the subsequent involuntary wrist motion to another position (natural unloading). Subjects then learned to diminish the post-unloading movement extent without activating antagonist (extensor) muscles before unloading or making intentional movement corrections after unloading (adjusted unloading). Although activity levels of wrist muscles before unloading were similar, MEPs of extensor but not pre-loaded flexor muscles were higher before adjusted unloading. We also applied TMS in combination with a torque pulse that shortened extensor muscles such that the MEP occurred when the motoneuronal excitability was minimized. Although diminished following muscle shortening, MEPs before adjusted unloading were still higher than before natural unloading. Results suggest that the corticospinal system, possibly together with other descending systems participated in the tonic subthreshold facilitation of antagonist motoneurons before adjusted unloading, which appears sufficient in modifying motor commands and motion leading to adjusted unloading. This study reinforces previous findings that descending systems, in particular, the corticospinal system can employ threshold position control during and after learning a novel action.     

Impaired modulation of motor cortex excitability by homonymous and heteronymous muscle afferents in focal hand dystonia.

A decrease of heteronymous median nerve-evoked inhibition of corticospinal projections to forearm extensor muscles was reported in a group of 10 dystonic patients by Bertolasi and colleagues in 2003. Here we tested the excitability of corticomotoneuronal connections to both wrist extensor (ECR) and flexor (FCR) muscles after conditioning stimulation of median and also radial nerve at rest in a group of 25 patients with focal hand dystonia compared to 20 healthy subjects. We also investigated the effect of the wrist dystonic posture, either in flexion or in extension, on the afferent modulation of ECR and FCR motor evolved potentials (MEPs). The heteronymous (median-induced) but also homonymous (radial-induced) inhibitions (interstimuli intervals 13-21 ms) of ECR MEP size observed in healthy subjects were decreased in patients. In addition, homonymous (median-induced) facilitation of FCR MEP size was also decreased in patients while heteronymous inhibition (radial-induced) was not. Neither the involvement of the target muscle in the dystonic posture nor the origin of the afferent volley (from a dystonic muscle) influenced the degree of impairment of afferent modulation of the MEP. These findings support the view that a global abnormal somatosensory coupling in focal hand dystonia may contribute to an inadequate motor command to wrist muscles.     

Effect of repetitive transcranial magnetic stimulation combined with robot-assisted training on wrist muscle activation post-stroke

ObjectiveTo compare the effects of active assisted wrist extension training, using a robotic exoskeleton (RW), with simultaneous 5 Hz (rTMS + RW) or Sham rTMS (Sham rTMS + RW) over the ipsilesional extensor carpi radialis motor cortical representation, on voluntary wrist muscle activation following stroke.MethodsThe two training conditions were completed at least one week apart in 13 participants >1-year post-stroke. Voluntary wrist extensor muscle activation (motor unit (MU) recruitment thresholds and firing rate modulation in a ramp-hold handgrip task), ipsilesional corticospinal excitability (motor evoked potential [MEP] amplitude) and transcallosal inhibition were measured Pre- and Post-training.ResultsFor MUs active both Pre and Post training, greater reductions in recruitment thresholds were found Post rTMS + RW training (p = 0.0001) compared to Sham rTMS + RW (p = 0.16). MU firing rate modulation increased following both training conditions (p = 0.001). Ipsilesional MEPs were elicited Pre and Post in only 5/13 participants. No significant changes were seen in ipsilesional corticospinal excitability and transcallosal inhibition measures (p > 0.05).ConclusionsFollowing a single rTMS + RW session in people >1-year post-stroke, changes were found in voluntary muscle activation of wrist extensor muscles. Alterations in ipsilesional corticospinal or interhemispheric excitability were not detected.SignificanceThe effects of rTMS + RW on muscle activation warrant further investigation as post-stroke rehabilitation strategy.     

On the focal nature of inhibition and facilitation in the human motor cortex.

OBJECTIVE: To find the area of the human cortex from which inhibition and facilitation of corticospinal neurons could be obtained. METHODS: A patient with seizures had an array of 64 electrodes placed over the left fronto-temporal cortex. The motor evoked potential (MEP) elicited by stimulating through one pair of electrodes was conditioned by stimuli that were subthreshold for a MEP given through adjacent pairs of electrodes. RESULTS: The MEP recorded over the right abductor pollicis brevis produced by stimulating over the hand area of the left cortex could be inhibited (at intervals less than 5 ms) and facilitated (at intervals greater than 5 ms) by subthreshold conditioning stimuli delivered through neighbouring pairs of electrodes. The inhibition and facilitation were only obtained when the conditioning stimuli were delivered within 1-2 cm of the test site. The sites producing inhibition and facilitation were not identical. Conditioning stimuli over the face area did not inhibit the MEP produced by stimulating the hand area or vice versa. CONCLUSION: The inhibition and facilitation of corticospinal neurons projecting to a given muscle arise from small areas close to those corticospinal neurons.     

Vision modulates corticospinal suppression in a functionally specific manner during movement of the opposite limb

The effect of vision on the excitability of corticospinal projections to the flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles of right human forearm was investigated before and during discrete movement of the opposite limb. An external force opposed the initial phase of the movement (wrist flexion) and assisted the reverse phase, so that recruitment of the wrist extensors was minimized. Three conditions were used as follows: viewing the inactive right limb (Vision), viewing the mirror image of the moving left limb (Mirror), and with vision of the right limb occluded (No Vision). Transcranial magnetic stimulation was delivered to the left motor cortex: before, at the onset of, or during the left limb movement to obtain motor evoked potentials (MEPs) in the muscles of the right forearm. At and following movement onset, MEPs obtained in the right FCR were smaller in the Vision condition than in the Mirror and No Vision conditions. A distinct pattern of variation was obtained for the ECR. In all conditions, MEPs in this muscle were elevated upon or following movement of the opposite limb. An additional analysis of ipsilateral silent periods indicated that interhemispheric inhibition plays a role in mediating these effects. Activity-dependent changes in corticospinal output to a resting limb during discrete actions of the opposite limb are thus directly contingent upon where one looks. Furthermore, the extent to which vision exerts an influence upon projections to specific muscles varies in accordance with the functional contribution of their homologs to the intended action.     

High-frequency transcutaneous electrical nerve stimulation (TENS) differentially modulates sensorimotor cortices: An MEG study

ObjectiveTranscutaneous electrical nerve stimulation (TENS) affects excitability of the central motor system as well as the somatosensory system. To determine whether TENS has influence on excitability in the sensorimotor cortices of TENS-treated finger muscle, we investigated magnetoencephalogram associated with voluntary, self-paced finger movement before and after TENS.MethodsHigh-frequency TENS was applied on the extensor digitorum muscle for 15 min. Subjects underwent alternate middle finger and thumb extension movements before and after the TENS. We recorded movement-related cortical magnetic field (MRCF) associated with TENS-treated middle finger movement and that from untreated thumb movement.ResultsThe current source for motor field (MF) was located in the pre-central motor cortex and anteriorly-oriented, and that for motor evoked field one (MEF1) was found in the post-central somatosensory cortex and posteriorly-oriented. The amplitude of MF for TENS-treated middle finger movement decreased but unchanged for untreated thumb movement after TENS. The amplitude of MEF1 decreased for either finger movement after TENS.ConclusionHigh-frequency TENS to the forearm muscle modulates excitability of the limited area of motor cortex but wider area of primary somatosensory cortex.SignificanceHigh-frequency TENS to the forearm muscle modulates excitability of the primary somatosensory cortex and motor cortex in a different manner.     

Modulation of motor cortex excitability after upper limb immobilization.

OBJECTIVE: To examine the mechanisms of disuse-induced plasticity following long-term limb immobilization. METHODS: We studied 9 subjects, who underwent left upper limb immobilization for unilateral wrist fractures. All subjects were examined immediately after splint removal. Cortical motor maps, resting motor threshold (RMT), motor evoked potential (MEP) latency and MEP recruitment curves were studied from abductor pollicis brevis (APB) and flexor carpi radialis (FCR) muscles with single pulse transcranial magnetic stimulation (TMS). Paired pulse TMS was used to study intracortical inhibition and facilitation. Compound muscle action potentials (CMAPs) and F waves were obtained after median nerve stimulation. In 4/9 subjects the recording was repeated after 35-41 days. RESULTS: CMAP amplitude and RMT were reduced in APB muscle on the immobilized sides in comparison to the non-immobilized sides and controls after splint removal. CMAP amplitude and RMT were unchanged in FCR muscle. MEP latency and F waves were unchanged. MEP recruitment was significantly greater on the immobilized side at rest, but the asymmetry disappeared during voluntary muscle contraction. Paired pulse TMS showed an imbalance between inhibitory and excitatory networks, with a prevalence of excitation on the immobilized sides. A slight, non-significant change in the strength of corticospinal projections to the non-immobilized sides was found. TMS parameters were not correlated with hand dexterity. These abnormalities were largely normalized at the time of retesting in the four patients who were followed-up. CONCLUSIONS: Hyperexcitability occurs within the representation of single muscles, associated with changes in RMT and with an imbalance between intracortical inhibition and facilitation. These findings may be related to changes in the sensory input from the immobilized upper limb and/or in the discharge properties of the motor units. SIGNIFICANCE: Different mechanisms may contribute to the reversible neuroplastic changes, which occur in response to long-term immobilization of the upper-limbs.     

Muscle imaging: mapping responses to transcranial magnetic stimulation with high-density surface electromyography

Representations of different body parts or muscles in the human primary motor cortex overlap extensively. At the effector level, most muscles are surrounded by and overlap with several neighbours as well. This hampers the assessment of excitability in individual muscles with transcranial magnetic stimulation (TMS), even if so-called "focal" stimulating coils are used. Here we used a novel mapping paradigm based on high-density surface electromyography (HD-sEMG) to investigate the spatial selectivity of TMS in the forearm musculature. In addition, we tested the hypothesis that selective stimulation can be improved by a voluntary background contraction of the target muscle. We mapped and compared the topographies of motor evoked potential (MEP) amplitudes during rest and during background contractions of two forearm muscles (extensor carpi radialis and extensor digitorum communis). The MEP topographies were also compared to the amplitude topography of voluntary EMG. The results indicate that under many conditions a large proportion of the MEP activity recorded at the surface originated from the target muscle's neighbours. There was a systematic relationship between TMS intensity and the topographic distribution of MEP responses during voluntary contraction. With increasing stimulus intensity, the MEP topography deviated increasingly more from the topography of voluntary EMG. We conclude that when standard EMG montages are used, the recorded MEPs are not necessarily evoked in the target muscle alone. Stimulation during a voluntary background contraction of the target muscle may enhance the selectivity of TMS. It however remains essential to use stimulus intensities as low as possible, to minimize the contribution of surrounding non-target muscles to the MEP.     

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.     

Impaired heteronymous somatosensory motor cortical inhibition in dystonia.

A typical pathophysiological abnormality in dystonia is cocontraction of antagonist muscles, with impaired reciprocal inhibitory mechanisms in the spinal cord. Recent experimental data have shown that inhibitory interactions between antagonist muscles have also a parallel control at the level of the sensorimotor cortex. The aim of this work was to study heteronymous effects of a median nerve stimulus on the corticospinal projections to forearm muscles in dystonia. We used the technique of antagonist cortical inhibition, which assesses the conditioning effect of median nerve afferent input on motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) in ipsilateral forearm extensor muscles at rest. Nine healthy subjects and 10 patients with torsion dystonia participated in the study. MEPs and somatosensory evoked potentials were normal in patients. In healthy subjects, median nerve stimulation at 15- to 18-msec intervals inhibited the test MEPs in forearm extensors. In dystonic patients, median nerve stimulation delivered at the same conditioning-test intervals elicited significantly less inhibition of the test MEP. On the whole, these data suggest an impaired sensory-motor integration in dystonia and, more specifically, the decreased antagonistic cortical inhibition could suggest that functional interactions between antagonist muscles are primarily impaired at the cortical level.     

Changes in corticomotor excitability following prolonged muscle tendon vibration

The present experiment addressed whether increases in corticospinal excitability following sensory stimulation with muscle tendon vibration are accompanied by reorganization of the forearm musculature representation within the primary motor cortex. Using transcranial magnetic stimulation, we mapped the corticomotor projection to the dominant flexor carpi radialis (FCR) and extensor carpi radialis brevis (ECR) muscle before and after interventional sensory stimulation obtained via muscle tendon vibration (80Hz, 60 min) to the dominant distal wrist flexor tendons. Following vibration, MEP amplitude at the optimal stimulation position, motor output area, as well as map volume, increased significantly for the ECR. None of these effects reached significance for the FCR. These results suggest that the antagonistic vibratory response (AVR), which is considered to be of cortical origin, induces a delayed facilitation of musculature that is antagonistic to the site of the directly activated Ia afferent pathways. This example demonstrates that peripheral sensory stimulation can induce lasting increases in corticospinal excitability in the absence of actual movements.     

Hand motor cortex activation in a patient with congenital mirror movements: a study of the silent period following focal transcranial magnetic stimulation

Motor evoked potentials (MEPs) to focal transcranial magnetic stimulation (TMS) have demonstrated that abnormal ipsilateral corticospinal projections are active in patients with congenital mirror movements. In addition, movement-related potentials and PET suggest that an abnormal pattern of motor cortex activation could be associated with an anomaly of the corticospinal tracts. In the present study the silent period (SP) following focal TMS was investigated in a woman with familial congenital mirror movements. Recordings were made from both the abductor pollicis brevis (APB) muscles. When focal TMS was delivered during an intended contralateral APB muscle contraction, MEP and SP were bilaterally recorded and SP was significantly shorter than the contralateral SP observed in normal controls. An abnormal bilateral activation of the hand motor cortex can explain our findings. The non-stimulated motor cortex causes an early partial recovery of the background EMG activity when the stimulated motor cortex is still inhibited (beginning as soon as the transcallosal and the short-lasting segmental inhibition are both complete.     

Inhibition of ipsilateral motor cortex during phasic generation of low force.

OBJECTIVE: To study the effect of different types of unilateral pinch grips on excitability of the ipsilateral motor cortex. METHODS: In 9 healthy volunteers, transcranial magnetic stimuli (TMS) were applied over one motor cortex while the subjects performed either phasic or tonic ipsilateral pinch grips with different force levels (range 1-40% maximum voluntary contraction, MVC). Motor evoked potentials (MEP) were recorded from the relaxed contralateral first dorsal interosseous muscle (FDI) and were compared to MEPs obtained during muscle relaxation of both hands. In additional experiments, transcranial electrical stimuli (TES) were administered and F waves were recorded after electrical stimulation of the ulnar nerve. RESULTS: Phasic pinch grips with low force (1 and 2% MVC) induced a significant decrease of TMS-induced MEP amplitudes. The effect lasted for about 100 ms after reaching the force level and was similar for both right and left-handed pinch grips. TES-induced MEPs and F waves remained unchanged. In contrast, tonic contractions (20 and 40% MVC) enhanced MEPs in the homologous FDI. CONCLUSIONS: Phasic pinch grips with low force inhibit the motor cortex responsible for the contralateral homologous hand muscle. This effect, which is probably mediated transcallosally, might act at the level of the motor cortex.     

Corticospinal excitability during motor imagery of a simple tonic finger movement in patients with writer's cramp.

Motor imagery (MI) is the mental rehearsal of a motor act without overt movement. Using transcranial magnetic stimulation (TMS), we tested the effect of MI on corticospinal excitability in patients with writer's cramp. In 10 patients with writer's cramp and 10 healthy controls, we applied focal TMS over each primary motor area and recorded motor evoked potentials (MEPs) from contralateral hand and arm muscles while participants imagined a tonic abduction of the index finger contralateral to the stimulated hemisphere. In healthy controls and patients, the MEP amplitude in the relaxed first dorsal interosseus muscle (FDI) showed a muscle-specific increase during MI; however, the increase was less pronounced in patients than in healthy controls. In addition, in patients but not in controls, the MEP amplitude also increased in hand and forearm muscles not involved in the imagined movement. This abnormal spread of facilitation was observed in the affected and unaffected upper limb. MI of simple hand movements is less efficient and less focussed in patients with writer's cramp than it is in normal subjects.     

A study of transcranial magnetic stimulation in older (>3 years) patients of malnutrition.

Transcranial magnetic stimulation was performed in 40 subjects. Twenty patients in the age group of 3 to 8 years and having different grades of malnutrition were included in the 'study group' whereas 20 normal children having no complaints comprised the 'control group'. The coil of the magnetic stimulator was applied tangentially over the vertex to stimulate the cortex. The motor evoked potential (MEP) was obtained using root stimulation by applying the coil at the cervical and lumbosacral spines. Recordings were made from the abductor pollicis brevis (APB) and extensor digitorum brevis (EDB) muscles of both sides. Cortical threshold, latency and amplitude of motor evoked potential and central conduction time were recorded. Malnourished children showed significantly increased cortical threshold, prolonged cortical latency and central conduction time and reduction in amplitude of MEP. Observed delay in central motor conduction in malnourished children suggests asymptomatic involvement of corticospinal pathways.     

Stimulus-response properties of motor system in patients with cerebellar ataxia.

OBJECTIVE: The aim of the study was to examine the stimulus-response properties of the excitatory and inhibitory components of corticospinal projections at rest and during voluntary contraction in cerebellar patients. METHODS: We investigated motor evoked potential (MEP) and cortical silent period recruitment curves in response to increasing intensities of transcranial magnetic stimulation in 8 patients with 'pure' cerebellar syndromes and in 14 age-matched controls. The transcranial magnetic stimulation intensity was increased from 90 to 180% of the resting motor threshold. MEP recruitment curves were recorded at rest and during voluntary contraction in the right abductor pollicis brevis muscle. RESULTS: No statistical differences were found between patients and controls in MEP recruitment curves in either the resting or active condition. A significant difference was found between patients and controls in the cortical silent period threshold (patients: 33.2+/-3.4% of maximal stimulator output; controls 39.4+/-3.2%; P=0.01) and recruitment curve, the duration of the cortical silent period being longer in patients at transcranial magnetic stimulation intensities ranging from 90 to 130% of the resting motor threshold (patients: 135-191 ms; controls: 53-158 ms). No changes were found in the silent period evoked by peripheral nerve stimulation. CONCLUSIONS: Inhibitory components of corticospinal projections were recruited with a lower threshold in patients. No abnormalities were found in the recruitment of the excitatory networks. Our data show a prevalence of inhibitory phenomena in the motor cortex of cerebellar patients. These findings would appear to be specific to cerebellar diseases and are the opposite of those previously documented in movement disorders such as dystonia and Parkinson's disease. Our results suggest that the cerebellum and the basal ganglia may counteract each other in modulating the level of motor system excitability.     

The effect of continuous theta burst stimulation over premotor cortex on circuits in primary motor cortex and spinal cord

ObjectiveTo understand the effect of continuous theta burst stimulation (cTBS) given to the premotor area, we studied the circuits within the primary motor cortex and spinal cord after cTBS over the dorsal premotor area (PMd).MethodsThree sets of parameters, including corticospinal excitability, short interval intracortical inhibition (SICI) and intracortical facilitation (ICF) and forearm reciprocal inhibition (RI) were tested.ResultsParalleling the effects of cTBS applied directly to the primary motor cortex, cTBS over the left PMd suppressed corticospinal excitability as measured by the change in the size of MEPs evoked by single pulse TMS over primary motor cortex. Premotor cTBS appeared to have a longer lasting, but no more powerful effect on corticospinal excitability than motor cTBS, however, unlike motor cTBS it had no effect on SICI or ICF. Finally, although premotor cTBS had no effect on spinal H-reflexes, it did reduce the third phase of RI between forearm extensor and flexor muscles.ConclusionsPremotor cTBS is a quick and useful way of modulating excitability in cortical and possibly subcortical motor circuits.SignificancePremotor cTBS can be used as an alternative to regular rTMS to evaluate cortical function, motor behaviours and the response to disease therapy.     

The after effects of motor cortex rTMS depend on the state of contraction when rTMS is applied.

OBJECTIVE: To test whether the after effects of 5 Hz focal rTMS over the primary motor cortex are modulated by the state of muscle contraction when the rTMS is applied. METHODS: Ten healthy volunteers gave informed consent to the studies. Fifty stimuli at active motor threshold intensity were applied at 5 Hz to the forearm motor area during 10% MVC isometric wrist flexion, 10% MVC wrist extension and at rest. Short interval intracortical inhibition (SICI: interstimulus intervals of 2-5 ms) and intracortical facilitation (interstimulus intervals of 7 and 10 ms) were recorded at rest before and after rTMS from flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles with surface electrodes. RESULTS: rTMS during wrist flexion decreased SICI in the FCR whereas SICI was increased if rTMS was given during wrist extension. The opposite was true in ECR: SICI was increased if rTMS was applied during wrist flexion, whereas it was reduced if rTMS was given during wrist extension. rTMS applied at rest produced a small overall decrease of SICI in FCR and ECR but this was not individually significant in the FCR. The 10 s wrist flexion without any rTMS did not have any effect on SICI. CONCLUSIONS: The after effects of motor cortex rTMS can be selectively modulated by the pattern of muscle contraction.