Timing of cortical excitability changes during the reaction time of movements superimposed on tonic motor activity (original) (raw)
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Electroencephalography and clinical neurophysiology, 1988
The time course of facilitation of motor evoked potentials (MEPs) to transcranial electrical stimulation delivered at varying intervals near the onset of a voluntary ballistic movement was studied in 4 normal subjects. MEPs were recorded from the left thenar muscles to unifocal anodal stimulation of the right scalp overlying the hand motor area delivered every 8-10 sec. A click, occasionally associated with the scalp stimulation (P = 0.3-0.6), was the signal for the subject to make a brief thumb press on a piston at short latency. The timing of the scalp stimulus and the click was adjusted so that the former occurred approximately between 100 msec before and 100 msec after the onset of the voluntary movement signaled by the EMG in the thenar muscles. MEPs were not detected when the scalp was stimulated 80 msec or more before onset of voluntary movement and then appeared with increasing probability as the time interval before movement shortened. The amplitudes of MEPs in the 80-40 ms...
Motor cortex excitability changes during imagery of simple reaction time
Experimental Brain Research, 2008
Imagining motor actions is enough to enhance cortical motor excitability. However, the fact that execution of the motor task has to be inhibited should have a correlate on the extent of cortical excitability enhancement. Therefore, we examined the possible differences between real and motor imagery of simple reaction time tasks (SRT) in the facilitation of the motor-evoked potential (MEP) to transcranial magnetic stimulation (TMS) and in the reduction of short-interval intracortical inhibition (SICI) taking place before the movement onset. Thirteen healthy volunteers were requested to perform visual real or imaginary SRT tasks (rSRT and iSRT) with their dominant hand. For rSRT, subjects had to perform a rapid isometric squeeze as soon as possible after the imperative signal. For iSRT they had to imagine the same movement without actually doing it. Electromyographic (EMG) signals were recorded from the first dorsal interosseus (FDI) muscle. The mean EMG onset was calculated for each subject in rSRT trials. Single-and paired-pulse TMS (at an interstimulus interval of 2.5 ms) were applied at rest and at time intervals of −25, −50, −75, −100 and −125 ms before the expected real (rSRT) mean EMG onset. In rSRT there was a significant increase of MEP to single-pulseTMS at the intervals of −50 and −25 ms, and in iSRT at −50 ms in comparison to the rest condition. % SICI changes were significantly reduced at the intervals of −75, −50 and −25 ms, before EMG the onset in rSRT and at −50 and −25 in iSRT (P < 0.05) in comparison to % SICI changes at rest. The differences between MEPs to spTMS and MEP to ppTMS were significantly larger at rest, −125 and −100 ms intervals in rSRT, and at all intervals in iSRT. Imagining to move causes an increase in corticospinal excitability and a decrease in intracortical inhibition that follow a temporal profile similar to those observed with real movements. However, complete removal of SICI happened only in rSRT at the shortest intervals before the EMG onset. Such action may delineate new tool in motor rehabilitation of patients who have limitation to move.
1992
Transcranial magnetic motor cortex stimulation can elicit a series of responses recorded with different latencies from relaxed muscles of the lower limbs. In 7 healthy subjects, ranging in age from 16 to 62 years, stimulation was delivered by a 9 cm coil centered over Cz with the subject in the supine position. Surface polyelectromyography was used to record motor evoked potentials (MEPs) from the quadriceps (QD), hamstrings (HS), tibialis anterior (TA) and triceps surae (TS) muscles bilaterally. Three characteristic responses were identified in each muscle group on the basis of amplitude and latency criteria, identified by latencies: the direct oligosynaptic response MEP30 appeared with a latency of 24.3 msec in the QD, 26.3 msec in the HS, 30.5 msec in the TA and 31.3 msec in the TS; MEP70 with latencies of 64 msec in the QD, 59 msec in the HS, 79 msec in the TA and 72 msec in the TS; MEPt20 with latencies of 115 msec in the QD, 126 msec in the HS, 117 msec in the TA and 124 msec in the TS. These 3 responses have distinct latencies, amplitudes and durations. MEP70 appears to be the result of activation of long descending tracts which end on spinal interneuronal circuits. As MEPt20 has different features, it may have a different mechanism.
Brain Research, 1995
Aim of the study was to analyze the characteristics of motor action potentials recruitment during magnetic trans-cranial stimulation (KS) of the brain. Coaxial needle recordings from hand and upper limb musculature, as well as surface electrodes were employed in 20 healthy controls during magnetic TCS with regular and figure-of-8 coil in different experimental protocols including: (a) simple reaction time paradigm during which TCS at subthreshold intensity for eliciting EPs in relaxation was delivered at various intervals between the signal to move and the onset of the voluntary EMG burst; (b) prathreshold TCS was randomly delivered while the subject was voluntarily firing at a regular rate one 'low' and/or 'high thre$!gold' motor unit action potcl**!~*I (MUAP), The pre-and post-TCS MWAPs recruitment as well as their firing rates were comphncd; (c) recordings with two separate needles picking up iradiuidrtal MUM% from the same or from two different muscles were obtained in order to test ,:+r?chrony" df MUAP's discharge before and after TCS; (d) the influence of the time-interval separating the last discharged MUAP ~~~~~ KS was evaluated, (e) differences between simultaneous surface and depth recordings were examined. The fdhing re~:dts wt+vc obtained. (a) The same low-amplitude MUAP which is first voluntarily rccruitcd at the onset of the E s thr NZ i:&ially fired by TCS in the prc-movcmcnt period. Latency shortenings and :$?nliQr& cn!XPrrri'nt of surface were uhsvr\~,~I with faster reaction times. Such changes wcrc coupled to the recruitment 01 hrgh-threshold MUAPs being in amplitude LN! briefer in latency than the initial one, (b) When usin suprathreshold TCS, MEPs followed by silent s were ft~nd, l'b s SP was followed by a rebound acceleration of the M APs firing rate compared with pre-TCS Icvcls.
Electroencephalography and clinical neurophysiology, 1993
We compared single motor unit and surface EMG responses in the active right tibialis anterior following anodal electrical or magnetic stimulation of the motor cortex over the vertex. Magnetic stimulation used a monophasic current pulse through a circular coil centred 3 cm anterior to the vertex. Lowest threshold magnetic stimulation occurred when the current in the coil flowed from the left to the right side at the posterior rim of the coil. Such stimulation produced single unit and surface EMG responses which had the same latency as those produced by anodal electric stimulation. If the direction of the magnetic stimulating current was reversed, response latencies became more variable from unit to unit, and on average they occurred 1.0 +/- 0.5 msec later. In single motor units anodal and magnetic post-stimulus time histogram (PSTH) peaks had the same duration. This was similar to the duration of the PSTH peaks produced by a single low intensity stimulus given to the common peroneal ...
European Journal of Neuroscience, 2002
The aim of this study was to determine the relative involvement of the corticospinal (CS) pathway in voluntarily controlled walking compared to unconstrained walking. In the voluntarily controlled walking condition, subjects had to walk at the same speed as in unconstrained walking with a mechanical constraint, which is known to affect speci®cally the upper-leg muscles. The motor cortex was activated transcranially using a focal magnetic stimulation coil in order to elicit motor evoked potentials (MEPs) in the rectus femoris (RF) and the biceps femoris (BF). The magnetic stimulation was delivered at the end of the swing (at 90% of the cycle duration), when the EMG backgrounds were similar in the two experimental conditions. For each subject in each condition, MEPs were measured for several stimulus intensities in order to establish the input/output (I/O) curve (MEPs amplitude plotted against stimulus strength). The results showed a signi®cant increase in the MEPs amplitude of both the RF and BF in voluntarily controlled walking compared to unconstrained walking, which is the ®rst evidence of cofacilitation of MEPs in antagonist upperleg muscles during human gait. In conclusion, although a lot of studies have emphasized a privileged input of the corticospinal pathway to the distal lower-leg muscles, this study shows that, if a locomotory task requires ®ne control of the proximal upper-leg muscles, a selective facilitation of MEPs is observed in these muscles.
Muscle & Nerve, 1996
~ ~ Vertex transcranial magnetic stimulation (TMS) elicited tibialis anterior motor evoked potentials (MEPs) and silent periods (SPs) that were recorded during and following isometric maximal volitional contraction (MVC). During MVC in 6 healthy subjects, MEP amplitudes in the exercised muscle showed an increasing trend from an initial value of 4539 t 809 pV (mean -c SE) to 550 -c 908 pV ( P < 0.13) while force and EMG decreased ( P < 0.01). Also, SP duration increased from 165 2 37 ms to 231 5 32 ms (P < 0.01). Thus, during a fatiguing MVC both excitatory and inhibitory TMS-induced responses increased. TMS delivered during repeated brief 10% MVC contractions before and after a fatiguing MVC in 5 subjects, showed no change in MEP amplitude but SP duration was prolonged after MVC. This SP prolongation was focal to the exercised muscle. Silent periods recorded after pyramidal tract stimulation were unchanged following the MVC. These results suggest that MEP and SP might have common sources of facilitation during an MVC and that inhibitory mechanisms remain focally augmented following a fatiguing MVC. o 1996 John Wiley & Sons, Inc.
Experimental Brain Research, 1997
The aim of the present study was to determine the characteristics of intracortical inhibition in the motor cortex areas representing lower limb muscles using paired transcranial magnetic (TMS) and transcranial electrical stimulation (TES) in healthy subjects. In the first paradigm (n=8), paired magnetic stimuli were delivered through a double cone coil and motor evoked potentials (MEPs) were recorded from quadriceps (Q) and tibialis anterior (TA) muscles during relaxation. The conditioning stimulus strength was 5% of the maximum stimulator output below the threshold MEP evoked during weak voluntary contraction of TA (335%). The test stimulus (672%) was 10% of the stimulator output above the MEP threshold in the relaxed TA. Interstimulus intervals (ISIs) from 1±15 ms were examined. Conditioned TA MEPs were significantly suppressed (P`0.01) at ISIs of less than 5 ms (relative amplitude from 20±50% of the control). TA MEPs tended to be only slightly facilitated at 9-ms and 10-ms ISIs. The degree of MEP suppression was not different between right and left TA muscles despite the significant difference in size of the control responses (P`0.001). Also, conditioned MEPs were not significantly different between Q and TA. The time course of TA MEP suppression, using electrical test stimuli, was similar to that found using TMS. In the second paradigm (n=2), the suppression of TA MEPs at 2, 3, and 4 ms ISIs was examined at three conditioning intensities with the test stimulation kept constant. For the pooled 2-to 4-ms ISI data, relative amplitudes were 346%, 615%, and 989% for conditioning intensities of 0.95, 0.90, and 0.85 active threshold, respectively (P`0.01). In conclusion, the suppression of lower limb MEPs following paired TMS showed similar characteristics to the intracortical inhibition previously described for the hand motor area.
Facilitation of responses to motor cortex stimulation: Effects of isometric voluntary contraction
Annals of Neurology, 1992
In 7 normal subjects we compared the facilitatory effect of isometric contraction of the tibialis anterior on the size of electromyographic responses evoked in this muscle by electric stimuli applied over the cervical column and by electric and magnetic percutaneous stimulation of the motor cortex. No significant difference was found between the degrees of facilitation of the responses to any of the stimuli. Using collision techniques, we also showed that the pyramidal fibers activated by spinal and cortical stimuli are the same. Facilitation induced by isometric contraction (20% maximum) was of similar or greater magnitude than that found with constant vibration of the tendon of the target muscle. In cases where vibration and contraction had equal facilitatory effects, there was no further facilitation of the responses when both conditions were applied together. These findings indicate that the facilitatory effect of isometric contraction of the target muscle essentially originates at a spinal level rather than in the motor cortex.
Muscle & Nerve, 1995
A single transcranial magnetic stimulus can evoke two involuntary muscle responses in lower limb muscles of healthy humans. The purpose of the present study was to find out if these responses, when evoked during the processing period of a simple or choice reaction time task, such as ankle dorsiflexion, have specific characteristics related to the task. During the auditory reaction time, a transcranial magnetic stimulus was delivered to observe changes in the excitability of the central nervous system. A dual-cone coil was used, which effectively stimulated the fairly deep-lying lower limb motor cortex. Stimuli were delivered in a random order with 20-300-ms delays from the auditory gosignal. Motor evoked potentials (MEP) in right and left anterior tibial and soleus muscles were analyzed while early MEPs were observed invariably in both muscles; late MEPs occurred consistently only in soleus muscles. Both early and late MEP amplitudes were larger in simple reaction time trials than in choice reaction time trials. The late MEP appeared earlier in the simple reaction time task than in the choice reaction time task, reflecting faster central processing of simple reaction time tasks. The amplitude of the soleus late MEP in the simple reaction time task followed closely the amplitude of anterior tibial early MEP, suggesting a preset agonist-antagonist organization. This relationship was not present in the choice reaction time task.