Ipsilateral Transcranial Magnetic Stimulation Research Articles

Hemisphere Asymmetry during Different Levels of Co-activation of Antagonist Muscles: a Transcranial Magnetic Stimulation Study

Contralateral and ipsilateral silent periods were recorded from first dorsal interosseous muscles of the dominant and the non-dominant hand in response to contralateral and ipsilateral transcranial magnetic stimulation (TMS) in twelve right-handed healthy volunteers during isometric index finger abduction and co-activation of antagonist muscles.
 In the dominant hand, contralateral silent period recorded during coactivation of antagonist muscles was significantly shorter than contralateral silent period recorded during isometric index finger abduction. In the nondominant hand, we did not find significant differences.
 In the dominant hand, ipsilateral silent period recorded during co-activation of antagonist muscles was significantly shorter than ipsilateral silent period recorded during isometric index finger abduction. In the non-dominant hand, we did not find significant differences.
 In conclusion, our main finding was the hemisphere asymmetry during co-activation of antagonist muscles. Both, contralateral and ipsilateral silent periods recorded from the dominant right hand were shorter in comparison to those recorded from the non-dominant hand. These findings illustrate the role of co-activation for the better and precise usage of the dominant hand.

Characterization of stimulus response curves obtained with transcranial magnetic stimulation from bilateral anterior digastric muscles in healthy subjects

Purpose The purpose of the study was to describe measurements of stimulus-response curves in the anterior digastric muscle (ADM) bilaterally following transcranial magnetic stimulation (TMS) to the right and left hemispheres. The first dorsal interosseous muscle (FDI) was the control muscle. Materials and methods The subjects were 20 healthy young adults. Test sessions determined motor thresholds (MT) and stimulus-response curves (1.0, 1.2, 1.4, 1.6 × MT) from either the FDI or ADM following TMS to left and right hemispheres using the double cone coil. Bilateral recordings of MEPs in the left and right ADM allowed us to generate stimulus response curves following ipsilateral and contralateral TMS. Results Intraclass correlation coefficients (ICC) for MEP amplitudes from ipsilateral and contralateral ADMs were >0.60 at motor threshold (MT) and >0.90 at stimulus intensities above MT. There was a linear increase in MEP amplitudes across stimulus intensities for the FDI following contralateral TMS, while MEP amplitudes from the ADM following contralateral and ipsilateral TMS increased linearly across stimulus intensities [F (3, 57) [Muscle × Recording Site × Stim Intensity] = 33.57; p < 0.05]; = 0.64). The slopes of the stimulus-response curve of the contralateral FDI was greater than the slopes of the stimulus response curves of the ipsilateral and contralateral ADM (p < 0.05). Conclusions The current study provided insights on the methodology for recording stimulus response curves in the ADM with TMS. These findings may translate into a valid, reliable, and relevant clinical outcome to study the pathophysiology of the corticobulbar motor system.

Absence of a Transcranial Magnetic Stimulation-Induced Lower Limb Corticomotor Response Does Not Affect Walking Speed in Chronic Stroke Survivors.

Background and Purpose- Transcranial magnetic stimulation is used to measure the functional integrity of the corticomotor system via motor evoked potentials (MEPs) in stroke. The association between corticomotor mechanisms and walking recovery is still not completely understood. This study determined the association between transcranial magnetic stimulation-induced MEPs and walking outcomes and examined the contribution of the contralesional hemisphere to walking recovery. Methods- Contralateral and ipsilateral transcranial magnetic stimulation responses from the contralesional and ipsilesional hemispheres were collected from 61 chronic stroke survivors. Clinical assessments included gait speeds, 6-minute walk distance, Timed Up and Go test, Fugl Meyer lower extremity scale, and strength measurements. Results- Stroke participants were classified based on the presence (MEP+ [n=28]) or absence (MEP- [n=33]) of MEPs in the paretic tibialis anterior and rectus femoris muscles. A between-group analyses showed no significant differences for any gait variable. MEP+ group showed significantly higher Fugl Meyer lower extremity and ankle dorsiflexor strength. Ipsilateral conductivity was not significantly different between groups. Finally, in the MEP+ group, MEP parameters did not predict gait recovery. Conclusions- Our study investigated the association between walking outcomes and neurophysiological parameters of lower limb function in a large cohort of stroke survivors. We did not find an associations between transcranial magnetic stimulation-induced tibialis anterior and rectus femoris MEPs and walking speeds. Further work is required to develop more comprehensive models in stroke for predicting walking recovery.

Probing the interaction of the ipsilateral posterior parietal cortex with the premotor cortex using a novel transcranial magnetic stimulation technique

ObjectiveFunctional imaging studies have shown that control of planned movement involves a distributed network that involves the premotor (PMv) and posterior parietal cortices (PPC). Similarly, anatomical studies show that these regions are densely interconnected via white matter tracts. We therefore hypothesized that the PPC influence over the motor cortex is partly via a connection with the PMv. MethodsUsing a novel three-pulse ipsilateral transcranial magnetic stimulation technique, we preconditioned the PPC (80% RMT) at ISIs from 4–15ms prior to stimulating the PMv and M1 at ISIs of 4 and 6ms. ResultsAs previously shown, PMv–M1 paired-pulse stimulation resulted in inhibition of the MEP (90% RMT, 4–6ms) and PPC–M1 paired-pulse stimulation resulted in facilitation of the MEP (90% RMT, 4–8ms). PPC–M1 paired-pulse stimulation at 80% RMT preconditioning had no effect on M1. PPC–PMv–M1 stimulation resulted in reversal of inhibition observed with PMv–M1 stimulation at ISIs ranging from 6 to 15ms. ConclusionsThe reversal of inhibition observed with PPC–PMv–M1 stimulation suggests that the parietal connection to the PMv plays a role in the modulation of M1. SignificanceThis is the first study to stimulate three intrahemispheric regions in order to test a disynaptic connection with M1. The described network may be important in a variety of movement disorders.

Long-latency TMS-evoked potentials during motor execution and inhibition

Transcranial magnetic stimulation (TMS) has often been used in conjunction with electroencephalography (EEG), which is effective for the direct demonstration of cortical reactivity and corticocortical connectivity during cognitive tasks through the spatio-temporal pattern of long-latency TMS-evoked potentials (TEPs). However, it remains unclear what pattern is associated with the inhibition of a planned motor response. Therefore, we performed TMS-EEG recording during a go/stop task, in which participants were instructed to click a computer mouse with a right index finger when an indicator that was moving with a constant velocity reached a target (go trial) or to avoid the click when the indicator randomly stopped just before it reached the target (stop trial). Single-pulse TMS to the left (contralateral) or right (ipsilateral) motor cortex was applied 500 ms before or just at the target time. TEPs related to motor execution and inhibition were obtained by subtractions between averaged EEG waveforms with and without TMS. As a result, in TEPs induced by both contralateral and ipsilateral TMS, small oscillations were followed by a prominent negative deflection around the TMS site peaking at approximately 100 ms post-TMS (N100), and a less pronounced later positive component (LPC) over the broad areas that was centered at the midline-central site in both go and stop trials. However, compared to the pattern in go and stop trials with TMS at 500 ms before the target time, N100 and LPC were differently modulated in the go and stop trials with TMS just at the target time. The amplitudes of both N100 and LPC decreased in go trials, while the amplitude of LPC decreased and the latency of LPC was delayed in both go and stop trials. These results suggested that TMS-induced neuronal reactions in the motor cortex and subsequent their propagation to surrounding cortical areas might change functionally according to task demand when executing and inhibiting a motor response.

Global Aphasia Without Hemiparesis

Global aphasia without hemiparesis (GAWH) is a rare stroke syndrome. Using transcranial magnetic stimulation (TMS), we evaluated 2 possible pathogenic mechanisms for GAWH: sparing of the decussated pyramidal tract, or alternatively, compensation by the ipsilateral pyramidal tract. Six patients were diagnosed to have GAWH by the Standard Language Test of Aphasia for Japanese. All patients underwent brain magnetic resonance (MR) imaging and angiography. According to the Trial of Org 10172 in Acute Stroke Treatment (TOAST) criteria, stroke subtype was determined as 3 patients with cardioembolic stroke, 2 with large-artery atherosclerosis, and 1 with another type. All patients underwent TMS, using a figure-of-8 coil, from 3 to 12 months after the onset, and motor evoked potentials were recorded on the abductor digiti minimi muscles. All patients had left-sided frontal or temporal lesions that were confirmed by MR diagnostic imaging. No motor evoked potential could be recorded by ipsilateral TMS. In 3 patients, brain stimulation on either side evoked the same amplitude on the contralateral abductor digiti minimi, whereas in the other 3 patients, the amplitude was suppressed on the right side. The infarction in the former patients was caused by cardioembolism and in the latter was not. In serial slices of brain MR imaging, the pyramidal tract was spared in the former and was involved to various degrees in the latter 3 patients. We recommend that GAWH was caused by the sparing of the decussated pyramidal tract. The pyramidal tract was intact in cases of GAWH caused by cardioembolism and subclinically impaired by other causes.

Influence of ipsilateral transcranial magnetic stimulation on the triphasic EMG pattern accompanying fast ballistic movements in humans

Fast ballistic flexion movements of the wrist are produced by a triphasic pattern of electromyographic (EMG) activity in flexor and extensor muscle. Whereas it is generally accepted that the primary motor cortex generates the first agonist burst (AG1), its contribution to the following antagonist burst (ANT) and second agonist burst (AG2) is unresolved. We applied single pulses of suprathreshold transcranial magnetic stimulation (TMS) at different times to the motor cortex ipsilateral to wrist flexion. This produced interhemispheric inhibition of the opposite motor cortex and a silent period in the ballistic EMG pattern that started about 30 ms after the stimulus and lasted for a further 30 ms. If the silence was timed to start within the first 30 ms of AG1, then timing of the subsequent ANT and AG2 bursts was delayed. However, if the silence began later, then the timing of the ANT burst was not changed. A similar effect on the onset latency of the AG2 was seen if the silence began in the first part of the ANT burst. The results are compatible with a model in which the triphasic pattern is not triggered as a single entity. Instead we suggest that each burst has its own trigger that occurs about 30-40 ms after the start of AG1 (or ANT). If AG1 (or ANT) is interrupted within this time period then this trigger, and hence later bursts, are delayed. If the interruption occurs after 30-40 ms it has no effect on the onset of later bursts since they have already been triggered.

Responses of single motor units in human masseter to transcranial magnetic stimulation of either hemisphere.

The corticobulbar inputs to single masseter motoneurons from the contra- and ipsilateral motor cortex were examined using focal transcranial magnetic stimulation (TMS) with a figure-of-eight stimulating coil. Fine-wire electrodes were inserted into the masseter muscle of six subjects, and the responses of 30 motor units were examined. All were tested with contralateral TMS, and 87 % showed a short-latency excitation in the peristimulus time histogram at 7.0 +/- 0.3 ms. The response was a single peak of 1.5 +/- 0.2 ms duration, consistent with monosynaptic excitation via a single D- or I1-wave volley elicited by the stimulus. Increased TMS intensity produced a higher response probability (n = 13, paired t test, P < 0.05) but did not affect response latency. Of the remaining motor units tested with contralateral TMS, 7 % did not respond at intensities tested, and 7 % had reduced firing probability without any preceding excitation. Sixteen of these motor units were also tested with ipsilateral TMS and four (25 %) showed short-latency excitation at 6.7 +/- 0.6 ms, with a duration of 1.5 +/- 0.3 ms. Latency and duration of excitatory peaks for these four motor units did not differ significantly with ipsilateral vs. contralateral TMS (paired t tests, P > 0.05). Of the motor units tested with ipsilateral TMS, 56 % responded with a reduced firing probability without a preceding excitation, and 19 % did not respond. These data suggest that masseter motoneurons receive monosynaptic input from the motor cortex that is asymmetrical from each hemisphere, with most low threshold motoneurons receiving short-latency excitatory input from the contralateral hemisphere only.

Effort-induced mirror movements

During sustained, fatiguing maximal voluntary contraction of muscles of one hand, muscles of the other hand gradually become activated also. Such effort-induced mirror movements indicate a decreased ability of the central nervous system (CNS) to selectively control individual muscles. We studied whether altered transcallosal inhibition (TCI) contributed to this phenomenon. TCI was determined in ten healthy subjects by measuring the ipsilateral silent period (iSP) and the contralateral silent period (cSP) during a sustained contraction of the abductor digiti minimi, induced by focal unihemispheric ipsilateral transcranial magnetic stimulation. Mirror movements occurred in all subjects in response to the effort. There was a bilateral increase in cSPs and a parallel increase in the iSP in the contralateral working muscle. In contrast, the iSP in the mirroring muscle remained unchanged, explained by a balance of increased crossed pyramidal inhibition (cSP) and decreased transcallosal inhibition. In finely tuned unimanual movements, mirroring activity of the contralateral hand is suppressed by TCI originating in the working hemisphere. During sustained, effortful contractions, the outflow of the contralateral hemisphere is increased due to reduced TCI. Effort-induced mirror contractions are thus the result of disinhibition of contralateral crossed projections rather than disinhibition of ipsilateral uncrossed pathways.

Motor control in simple bimanual movements: a transcranial magnetic stimulation and reaction time study

Objective: Simple reaction time (RT) can be influenced by transcranial magnetic stimulation (TMS) to the motor cortex. Since TMS differentially affects RT of ipsilateral and contralateral muscles a combined RT and TMS investigation sheds light on cortical motor control of bimanual movements. Methods: Ten normal subjects and one subject with congenital mirror movements (MM) were investigated with a RT paradigm in which they had to move one or both hands in response to a visual go-signal. Suprathreshold TMS was applied to the motor cortex ipsilateral or contralateral to the moving hand at various interstimulus intervals (ISIs) after presentation of the go-signal. EMG recordings from the thenar muscles of both hands were used to determine the RT. Results: TMS applied to the ipsilateral motor cortex shortened RT when TMS was delivered simultaneously with the go-signal. With increasing ISI between TMS and go-signal the RT was progressively delayed. This delay was more pronounced if TMS was applied contralateral to the moving hand. When normal subjects performed bimanual movements the TMS-induced changes in RT were essentially the same as if they had used the hand in an unimanual task. In the subject with MM, TMS given at the time of the go-signal facilitated both the voluntary and the MM. With increasing ISI, however, RT for voluntary movements and MM increased in parallel. Conclusions: Ipsilateral TMS affects the timing of hand movements to the same extent regardless of whether the hand is engaged in an unimanual or a bimanual movement. It can be concluded, therefore, that in normal subjects simple bimanual movements are controlled by each motor cortex independently. The results obtained in the subject with MM are consistent with the hypothesis that mirror movements originate from uncrossed corticospinal fibres. The alternative hypothesis that a deficit in transcallosal inhibition leads to MM in the contralateral motor cortex is not compatible with the presented data, because TMS applied to the motor cortex ipsilateral to a voluntary moved hand affected voluntary movements and MM to the same extent.

Bilateral cortical control of the human anterior digastric muscles.

Transcranial magnetic stimulation (TCMS) was used to determine the organization of cortical motor projections to the anterior digastric muscles in 12 normal human subjects. Two distinct types of potentials were evoked in anterior digastric with a figure-of-eight coil. A short-latency (3 ms) response appeared bilaterally on the surface electromyogram (EMG), but only ipsilaterally on intramuscular recordings: this was the result of direct stimulation of the ipsilateral trigeminal motor root. Motor evoked potentials (MEPs) were elicited in the anterior digastric muscles at variable onset latencies of around 10 ms by stimulation of scalp areas antero-lateral to the area for the first dorsal interosseous muscle of the hand. These were evoked bilaterally in relaxed anterior digastric muscles in six of the seven subjects. In the other subject, the responses in the relaxed muscle were exclusively ipsilateral. However, when the anterior digastric muscles were contracted, the responses were bilateral in all subjects. TCMS and spike-triggered averaging revealed that the bilateral responses were not due to the branching of axons from individual digastric motoneurones to muscles on each side. Because the digastric motor nucleus may contain separate populations of ipsi- and contralateral projecting motoneurones, it was necessary to study single motor-unit responses to TCMS to demonstrate a bilateral corticobulbar projection. The responses of 17 single motor units in the anterior digastric muscle to TCMS were recorded. All were activated by contralateral stimulation. Approximately 80% were also activated by ipsilateral TCMS, although one well-characterised motor unit was inhibited by ipsilateral TCMS. When bilateral activation was present, the ipsilateral responses were more secure than the contralateral responses, which may indicate an additional interneurone in the pathway to the contralateral motoneurone. The major conclusions from this study are that (1) the cortical representation of the anterior digastric muscle is antero-lateral to hand muscles; (2) the cortical projection to the anterior digastric muscles is bilateral; (3) the corticobulbar projection is stronger contralaterally than ipsilaterally but may involve at least one additional synapse; and (4) anterior digastric motoneurones do not branch to innervate the muscles bilaterally.

Role of the ipsilateral motor cortex in mirror movements.

The mechanism of mirror movements in two patients was investigated; one with congenital mirror movement, the other with schizencephaly. Transcranial magnetic stimulation on one side elicited motor evoked potentials (MEPs)...