Biomedical subjects

John C Rothwell

Publications and source records attributed to John C Rothwell.

At least 55 records · Page 3Linked to original sources

PubMed2005

Stimulation through electrodes implanted near the subthalamic nucleus activates projections to motor areas of cerebral cortex in patients with Parkinson's disease.

High-frequency electrical stimulation through electrodes implanted in the subthalamic nucleus (STN) has been shown to reduce significantly the cardinal symptoms of Parkinson's disease (PD). Despite the success of this treatment, the mechanisms of action of stimulation are poorly understood. To elucidate further the mechanisms of action of deep brain stimulation and its effects on cortical activity, we recorded electroencephalographic potentials from 61 scalp-surface electrodes during low-frequency (5-10 Hz) bipolar stimulation in 11 patients with advanced PD (14 implanted electrodes were tested). In all electrodes tested, stimulation through at least one of the four contacts produced a medium-latency waveform with an average onset of 14 +/- 3 ms and peak at 23 +/- 4 ms. This potential typically increased in magnitude across contacts from ventral to dorsal. Within-subject comparisons of median nerve somatosensory evoked potentials demonstrated that the generator of the medium-latency potential was within the primary sensorimotor cortex or lateral premotor cortex ipsilateral to stimulation. The timing and topography of this potential were consistent with indirect activation of the cortex by excitation of pallido-thalamic axons that traverse the dorsal aspect of the STN. The potential evoked by stimulation through the contact used for optimal clinical effect was highly variable across electrodes and frequently different from the medium-latency potential described above, suggesting that the neuronal elements mediating the medium-latency potential were different from those that mediate the clinical effects.

Adult↗

PubMed2005

How does transcranial DC stimulation of the primary motor cortex alter regional neuronal activity in the human brain?

Transcranial direct current stimulation (tDCS) of the primary motor hand area (M1) can produce lasting polarity-specific effects on corticospinal excitability and motor learning in humans. In 16 healthy volunteers, O positron emission tomography (PET) of regional cerebral blood flow (rCBF) at rest and during finger movements was used to map lasting changes in regional synaptic activity following 10 min of tDCS (+/-1 mA). Bipolar tDCS was given through electrodes placed over the left M1 and right frontopolar cortex. Eight subjects received anodal or cathodal tDCS of the left M1, respectively. When compared to sham tDCS, anodal and cathodal tDCS induced widespread increases and decreases in rCBF in cortical and subcortical areas. These changes in rCBF were of the same magnitude as task-related rCBF changes during finger movements and remained stable throughout the 50-min period of PET scanning. Relative increases in rCBF after real tDCS compared to sham tDCS were found in the left M1, right frontal pole, right primary sensorimotor cortex and posterior brain regions irrespective of polarity. With the exception of some posterior and ventral areas, anodal tDCS increased rCBF in many cortical and subcortical regions compared to cathodal tDCS. Only the left dorsal premotor cortex demonstrated an increase in movement related activity after cathodal tDCS, however, modest compared with the relatively strong movement-independent effects of tDCS. Otherwise, movement related activity was unaffected by tDCS. Our results indicate that tDCS is an effective means of provoking sustained and widespread changes in regional neuronal activity. The extensive spatial and temporal effects of tDCS need to be taken into account when tDCS is used to modify brain function.

Adult↗

PubMed2005

High-frequency repetitive transcranial magnetic stimulation over the hand area of the primary motor cortex disturbs predictive grip force scaling.

When we repetitively lift an object, our grip force is influenced by the mechanical object properties of the preceding lift, irrespective of whether the subsequent lift is performed with the same hand or the hand opposite to the preceding lift. This study investigates if repetitive high-frequency transcranial magnetic stimulation (rTMS) over the dominant primary motor cortex affects this relationship. After completion of 10 lifts of an object using the dominant hand, rTMS was applied over the dominant primary motor cortex for 20 s. On the first lift following rTMS, the peak grip force was significantly higher than on the lift preceding rTMS. Moreover, this measure remained elevated throughout the following set of lifts after rTMS. rTMS did not change the peak lift force generated by more proximal arm muscles. The same effect was observed when the lifts following rTMS over the dominant motor cortex were performed with the ipsilateral hand. These effects were not observed when subjects rested both hands on their lap or when a sham stimulation was applied for the same period of time. These preliminary data suggest that rTMS over the sensorimotor cortex disturbs predictive grip force planning.

Adult↗

PubMed2004

Abnormal cortical and spinal inhibition in paroxysmal kinesigenic dyskinesia.

Paroxysmal kinesigenic dyskinesia (PKD) is characterized by brief episodes of choreic/dystonic movements precipitated by sudden movement. The condition responds to antiepileptic medication, particularly carbemazepine. Autosomal dominant inheritance is often seen, and a locus in the pericentromeric region of chromosome 16 has been identified in some families. Little is known of the pathophysiology of PKD, although an ion channel abnormality is thought likely. We assessed a number of electrophysiological parameters in 11 patients with idiopathic PKD, a proportion of them on and off treatment. We identified reduced short intracortical inhibition (SICI), reduced early phase of transcallosal inhibition, and a reduced first phase of spinal reciprocal inhibition (RI) in subjects with PKD. The cortical silent period, the startle response and the second and third phases of RI were normal. Treatment with carbamazepine normalized the abnormalities in transcallosal inhibition, but had no effect on other parameters. Patients with PKD show a discrete set of abnormalities in cortical and spinal inhibitory circuits that differ from those seen in primary dystonia and epilepsy, and which may provide clues to the underlying pathophysiology of the disorder.

Adolescent↗

PubMed2004

A sound-evoked vestibulomasseteric reflex in healthy humans.

Averaged responses to loud clicks were recorded in the unrectified and rectified masseter electromyogram (EMG) of 18 healthy subjects. Unilateral clicks (0.1 ms, 3 Hz, 70-100 dB NHL), delivered during a steady masseter contraction, evoked bilateral responses that appeared to consist of 2 components on the basis of threshold, latency, and their appearance in rectified EMG. The lowest threshold response appeared as a p16 wave (onset 11-13 ms) in the unrectified EMG and corresponded with a 10- to 12-ms period of inhibition in the rectified EMG. Higher-intensity clicks recruited an earlier p11 response in the unrectified EMG (onset 7.0-9.2 ms) that sometimes appeared as an initial increase in the rectified EMG before suppression. The amplitude of the p11 wave scaled with background EMG level and was asymmetrically modulated by 30 degrees tilt of the whole body. The threshold of the early p11/n15 wave in masseter was the same as the threshold for click-induced vestibulocollic reflexes. Single motor unit recordings demonstrated that responses in masseters corresponded to a silent period in unit firing that began earlier and lasted longer at 100 dB than at 80 dB. We propose that loud clicks induce 2 partially overlapping short-latency reflexes in masseter muscle EMG: a p11/n15 response, which we suggest is of vestibular origin, and a p16/n21 response, which we suggest is equivalent to the previously described jaw-acoustic reflex.

Acoustic Stimulation↗

PubMed2004

Preconditioning with transcranial direct current stimulation sensitizes the motor cortex to rapid-rate transcranial magnetic stimulation and controls the direction of after-effects.

BACKGROUND: Rapid-rate repetitive transcranial magnetic stimulation (rTMS) can produce a lasting increase in cortical excitability in healthy subjects or induce beneficial effects in patients with neuropsychiatric disorders; however, the conditioning effects of rTMS are often subtle and variable, limiting therapeutic applications. Here we show that magnitude and direction of after-effects induced by rapid-rate rTMS depend on the state of cortical excitability before stimulation and can be tuned by preconditioning with transcranial direct current stimulation (tDCS). METHODS: Ten healthy volunteers received a 20-sec train of 5-Hz rTMS given at an intensity of individual active motor threshold to the left primary motor hand area. This interventional protocol was preconditioned by 10 min of anodal, cathodal, or sham tDCS. We used single-pulse TMS to assess corticospinal excitability at rest before, between, and after the two interventions. RESULTS: The 5-Hz rTMS given after sham tDCS failed to produce any after-effect, whereas 5-Hz rTMS led to a marked shift in corticospinal excitability when given after effective tDCS. The direction of rTMS-induced plasticity critically depended on the polarity of tDCS conditioning. CONCLUSIONS: Preconditioning with tDCS enhances cortical plasticity induced by rapid-rate rTMS and can shape the direction of rTMS-induced after-effects.

Adult↗

PubMed2004

Increased corticospinal excitability after 5 Hz rTMS over the human supplementary motor area.

Transcranial magnetic stimulation (TMS) can produce effects not only at the site of stimulation but also at distant sites to which it projects. Here we examined the connection between supplementary motor area (SMA) and the hand area of the primary motor cortex (M1(Hand)) by testing whether prolonged repetitive TMS (rTMS) over the SMA can produce changes in excitability of the M1(Hand) after the end of the stimulus train. We evaluated motor-evoked potentials (MEPs) and the cortical silent period (CSP) evoked by a single-pulse TMS, short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) produced by a paired-pulse TMS, and forearm flexor H reflexes before and after 750 pulses of 5 Hz rTMS over SMA at an intensity of 110% active motor threshold (AMT) for the first dorsal interosseous (FDI) muscle. The amplitude of MEPs recorded from the right FDI muscle at rest as well as during voluntary contraction increased for at least 10 min after the end of rTMS, although the duration of the CSP, SICI and ICF did not change. There was no effect on H reflexes in the flexor carpi radialis muscle, even though the amplitude of the MEP obtained from the same muscle increased after rTMS. The effects on MEPs depended on the intensity of rTMS and were spatially specific to the SMA proper. We suggest that 5 Hz rTMS over SMA can induce a short-lasting facilitation in excitability of the M1(Hand) compatible with the anatomical connections between SMA and the M1(Hand).

Adult↗

PubMed2004

Subthreshold low-frequency repetitive transcranial magnetic stimulation over the premotor cortex modulates writer's cramp.

Writer's cramp, or focal hand dystonia, is characterized by involuntary coactivation of antagonist or unnecessary muscles while writing or performing other tasks. Although the mechanism underlying this muscle overactivation is unknown, recent studies of changes in cerebral blood flow during writing have demonstrated a reduction in the activation of the primary motor cortex (MC) and hyperactivity of parts of the frontal non-primary motor areas. Therefore, any measures that decrease the activities of non-primary motor areas such as the premotor cortex (PMC) and the supplementary motor area (SMA) might improve dystonic symptoms. To explore this possibility, we studied nine patients with writer's cramp and seven age-matched control subjects, using subthreshold low-frequency (0.2 Hz) repetitive transcranial magnetic stimulation (rTMS), which exerts an inhibitory action on the cortex. Previous studies have demonstrated shortened cortical silent periods in dystonia, suggesting deficient cortical inhibition in the MC. We compared the silent periods and computer-assisted ratings of handwriting before and after rTMS applied to the MC, SMA or PMC. We also used the sham coil for control runs. Stimulation of the PMC but not the MC significantly improved the rating of handwriting (mean tracking error from the target, P = 0.004; pen pressure, P = 0.01) and prolonged the silent period (P = 0.02) in the patient group. rTMS over the other sites or using a sham coil in the patient group or trials in the control group revealed no physiological or clinical changes. This increased susceptibility of the PMC in dystonia suggests that the lack of inhibition in the MC is secondary to the hyperactivity of PMC neurons. Inhibition of the PMC using rTMS could provide a therapeutic measure of writer's cramp.

Adult↗

PubMed2004

Interhemispheric interaction between human dorsal premotor and contralateral primary motor cortex.

We used transcranial magnetic stimulation (TMS) in a paired pulse protocol to investigate interhemispheric interactions between the right dorsal premotor (dPM) and left primary motor cortex (M1) using interstimulus intervals of 4, 6, 8, 10, 12, 16 and 20 ms in ten healthy subjects. A conditioning stimulus over right dPM at an intensity of either 90 or 110% resting motor threshold (RMT) suppressed motor-evoked potentials (MEPs) evoked in the first dorsal interosseous (FDI) muscle by stimulation of left M1. Maximum effects occurred for interstimulus intervals (ISIs) of 8-10 ms. There was no effect if the conditioning stimulus was applied 2.5 cm lateral, anterior or medial to dPM. The effect differed from previously described M1 interhemispheric inhibition in that the threshold for the latter was greater than 90% RMT, whereas stimulation of the dPM at the same intensity led to significant inhibition. In addition, voluntary contraction of the left FDI (i.e. contralateral to the conditioning TMS) enhanced interhemispheric inhibition from right M1 but had no effect on the inhibition from right dPM. Finally, conditioning to right dPM at 90% RMT reduced short-interval intracortical inhibition (SICI; at ISI = 2 ms) in left M1 whilst there was no effect if the conditioning stimulus was applied to right M1. We conclude that conditioning TMS over dPM has effects that differ from the previous pattern of interhemispheric inhibition described between bilateral M1s. This may reflect the existence of commissural fibres between dPM and contralateral M1 that may play a role in bimanual coordination.

Adult↗

PubMed2004

The effect of sensory input and attention on the sensorimotor organization of the hand area of the human motor cortex.

Sensory input can remodel representations in the sensory cortex, and this effect is heavily influenced by attention to the stimulus. Here we ask whether pure sensory input can also influence the spatial distribution of sensory effects on motor cortical hand area (sensorimotor organization) and whether this is modulated by attention. Sensorimotor organization was tested by applying short (1.5 s) periods of low amplitude vibration to single intrinsic hand muscles and measuring motor cortex excitability with transcranial magnetic stimulation (TMS). In healthy subjects, sensorimotor organization in the hand is focal, with input from one hand muscle increasing motor-evoked potentials (MEPs), decreasing short and increasing long-interval intracortical inhibition (SICI and LICI) in the vibrated muscle ('homotopic' effects) and having opposite effects on neighbouring muscles ('heterotopic' effects). Here we show that a 15 min intervention of vibration applied simultaneously to two hand muscles can lead to long-term (> 30 min) changes in the spatial pattern of sensorimotor interaction. The amount and direction of the effects depended on the subject's attention during the intervention: if subjects attended to both muscles when they were receiving simultaneous vibration, subsequent short-term vibration applied to one of them produced 'homotopic' effects on both muscles. 'Heterotopic' effects on a muscle not vibrated during the intervention were unaffected. If subjects did not attend to simultaneous vibration, subsequent short-term vibration of the muscles involved in the intervention no longer had any effect on them although the 'heterotopic' effects on a muscle not involved in the intervention were unchanged. We conclude that a 15 min period of pure sensory input can remodel the way that subsequent sensory inputs interact with motor output, that the effects are specific for the motor output to muscles involved in the intervention and that they are modulated by the subject's attention.

Adult↗

PubMed2004

Relaxation from a voluntary contraction is preceded by increased excitability of motor cortical inhibitory circuits.

Termination of a muscle contraction is as important a part of movement as muscle activation yet the mechanisms responsible are less well understood. In the present experiments we examined the possible role of intracortical inhibitory circuits in terminating a 20% maximum isometric contraction of the first dorsal interosseous muscle (FDI) in eight healthy subjects. Subjects performed the task simultaneously with both hands and received single or pairs (at an interstimulus interval of 3 ms to evaluate short interval intracortical inhibition, SICI) of transcranial magnetic stimuli (TMS) via a focal coil over the motor hand area of the left hemisphere at different times before and after the onset of relaxation. The amplitude of the motor-evoked potential (MEP) following a single or a pair of TMS pulses was measured in the right FDI and plotted relative to the onset of relaxation as estimated from the surface electromyogram (EMG) of the left FDI. MEPs were larger during contraction than after relaxation whereas SICI was absent during contraction and reappeared after relaxation. We found that in all subjects, the time course of MEP changes during relaxation was closely fitted by a Boltzmann sigmoidal curve which allowed us to estimate the mean MEP amplitudes as well as the ratio of the amplitudes after single or pairs of TMS pulses (i.e.%SICI) at any time in the task. The data showed that the amplitude of MEPs to single pulse TMS had started to decline at about the same time as the onset of EMG silence. Furthermore, the size of the MEPs evoked by paired pulses decreased up to 30 ms beforehand. The latter suggests that an increase in SICI occurs prior to the onset of MEP changes, and hence that increased cortical inhibition may play a role in suppressing corticospinal excitability during relaxation. A subsidiary experiment showed that the time relations of changes in SICI and MEP were unchanged by a period of 10 min training on the task.

Adult↗

PubMed2004

The right dorsolateral prefrontal cortex is essential in time reproduction: an investigation with repetitive transcranial magnetic stimulation.

This study used repetitive transcranial magnetic stimulation (rTMS) to investigate the roles of the right dorsolateral prefrontal cortex (DLPFC) and supplementary motor area (SMA) in short (500 ms) and long (2 s) interval timing. The results were compared with rTMS over the leg area of motor cortex, an area not thought to be involved with time estimation. rTMS was delivered during one of two phases of a time reproduction task: at the onset of the Estimation Phase (presentation of the interval to be timed) and at the onset of the Reproduction Phase (subjects' reproduction of the timed interval). There was a significant main effect of Site (SMA vs. right DLPFC vs. leg motor area) due to the fact that rTMS over the right DLPFC caused subjects to underestimate time intervals compared with rTMS over the leg motor area. There was also a significant three-way interaction between Site, Duration and Phase (Estimation Phase vs. Reproduction Phase) that post hoc analyses showed was due to underestimation of long intervals when rTMS was given over the right DLPFC at the start of the Reproduction Phase. There was no effect of rTMS over the right DLPFC or SMA in the short interval task. This is consistent with previous studies showing that the right DLPFC is important in estimating time intervals in the seconds-range. In addition, we suggest that the selectivity of the rTMS effect for the Reproduction Phase indicates that the right DLPFC plays a particular role in memory processes.

Adult↗

PubMed2004

Preconditioning of low-frequency repetitive transcranial magnetic stimulation with transcranial direct current stimulation: evidence for homeostatic plasticity in the human motor cortex.

Recent experimental work in animals has emphasized the importance of homeostatic plasticity as a means of stabilizing the properties of neuronal circuits. Here, we report a phenomenon that indicates a homeostatic pattern of cortical plasticity in healthy human subjects. The experiments combined two techniques that can produce long-term effects on the excitability of corticospinal output neurons: transcranial direct current stimulation (TDCS) and repetitive transcranial magnetic stimulation (rTMS) of the left primary motor cortex. "Facilitatory preconditioning" with anodal TDCS caused a subsequent period of 1 Hz rTMS to reduce corticospinal excitability to below baseline levels for >20 min. Conversely, "inhibitory preconditioning" with cathodal TDCS resulted in 1 Hz rTMS increasing corticospinal excitability for at least 20 min. No changes in excitability occurred when 1 Hz rTMS was preceded by sham TDCS. Thus, changing the initial state of the motor cortex by a period of DC polarization reversed the conditioning effects of 1 Hz rTMS. These preconditioning effects of TDCS suggest the existence of a homeostatic mechanism in the human motor cortex that stabilizes corticospinal excitability within a physiologically useful range.

Adult↗

PubMed2004

Inter-hemispheric asymmetry of ipsilateral corticofugal projections to proximal muscles in humans.

Motor evoked potentials (MEPs) elicited in many proximal or truncal muscles by ipsilateral transcranial magnetic stimulation (TMS) are thought to be mediated by an oligosynaptic corticofugal pathway and not by uncrossed corticospinal collaterals. In the present study, we compared the input-output properties and scalp surface topography of the ipsilateral and contralateral projections to pectoralis major (PM) and latissimus dorsi (LD) in seven healthy subjects. In six subjects, ipsilateral MEPs evoked by stimulation of one hemisphere (dominant ipsilateral hemisphere) were markedly larger in amplitude than the MEPs evoked in the opposite hemisphere (non-dominant ipsilateral hemisphere). The dominant ipsilateral hemisphere MEPs were significantly larger than the non-dominant MEPs (p<0.02) by an average factor of 3.6 and 3.4 times in PM and LD, respectively. Similarly, there was significant asymmetry between hemispheres in the scalp surface area from which ipsilateral MEPs could be evoked. In contrast, contralateral projections were symmetric in both MEP amplitude and area. Neither the right nor left hemisphere was consistently the dominant ipsilateral hemisphere. The ipsilateral centre of gravity (CoG) for PM was located an average of 0.8+/-0.6 cm posterior to the contralateral CoG, but no significant differences were observed between ipsilateral and contralateral CoGs in LD. These results demonstrate that the excitability of ipsilateral corticofugal projections to PM and LD are asymmetric between hemispheres.

Adult↗

PubMed2004

Consolidation of dynamic motor learning is not disrupted by rTMS of primary motor cortex.

Motor skills, once learned, are often retained over a long period of time. However, such learning first undergoes a period of consolidation after practice. During this time, the motor memory is susceptible to being disrupted by the performance of another motor-learning task. Recently, it was shown that repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex could disrupt the retention of a newly learned ballistic task in which subjects had to oppose their index finger and thumb as rapidly as possible. Here we investigate whether the motor cortex is similarly involved during the consolidation that follows learning novel dynamics. We applied rTMS to primary motor cortex shortly after subjects had either learned to compensate for a dynamic force field applied to their index finger or learned a ballistic finger abduction task. rTMS severely degraded the retention of the learning for the ballistic task but had no effect on retention of the dynamic force-field learning. This suggests that, unlike learning of simple ballistic skills, learning of dynamics may be stored in a more distributed manner, possibly outside the primary motor cortex.

Adult↗

PubMed2004

One-Hz repetitive transcranial magnetic stimulation of the premotor cortex alters reciprocal inhibition in DYT1 dystonia.

Repetitive transcranial magnetic stimulation (rTMS) can produce long-lasting effects not only underneath the site of stimulation, but also at distant connected sites. This study aimed to assess how low frequency rTMS over the premotor area might affect abnormalities in spinal motor function in patients with generalised dystonia associated with the DYT1 gene mutation. We assessed reciprocal inhibition (RI) in a group of 8 manifesting carriers of the DYT1 gene (DYT1) and 10 healthy controls. All subjects then received 20 minutes of 1 Hz rTMS over the premotor area, and RI was assessed again. Before rTMS, the second and third phases of RI were abnormal in DYT1 subjects compared to controls. After 20 minutes of 1 Hz rTMS over the premotor area, a significant increase in inhibition was noted in the third and possibly the first phase of RI in the DYT1 group. No changes in RI were observed in control subjects after rTMS. We have shown for the first time to date that reducing cortical excitability in patients with dystonia using rTMS can produce corresponding changes in abnormal spinal motor output. These findings make a case for further exploring rTMS as a tool to modulate abnormal cortical and spinal excitability in individuals with dystonia and even as a potential form of treatment for dystonic symptoms.

Adult↗

PubMed2004

Natural history and syndromic associations of orthostatic tremor: a review of 41 patients.

Orthostatic tremor (OT) is a rare condition characterized by unsteadiness when standing still that is relieved when sitting or walking and is thought to arise from a central generator in the cerebellum or brainstem. OT is considered to be a distinct, discrete condition, and little is known about its demographic characteristics, natural history, associated features, and treatment response. We have reviewed these aspects in 41 OT patients fulfilling current diagnostic criteria, seen at our institution between 1986 and 2001. We classified 31 (75%) as having idiopathic "primary OT" either with (n = 24) or without an associated postural arm tremor. We found that 10 of 41 (25%) cases had additional neurological features, and we defined this group as having "OT plus" syndrome. Of these 10, 6 had parkinsonism; 4 of these had typical Parkinson's disease (PD), 1 had vascular and 1 had drug-induced parkinsonism. Among the remaining 4 patients, 2 had restless legs syndrome (RLS), 1 had tardive dyskinesia, and 1 orofacial dyskinesias of uncertain etiology. One patient with PD and the patient with vascular parkinsonism also had RLS. Age at onset was significantly earlier in the "primary OT" (mean +/- SD, 50.4 +/- 15.1) than in the "OT plus" (61.8 +/- 6.4; z = 2.7; P =.006) group. In 7 of the 10 "OT plus" patients, OT leg symptoms preceded the onset of additional neurological features. OT appeared to be underdiagnosed, and on average, it took 5.7 years from the initial complaints until a diagnosis was made. In general, treatment response to a variety of drugs such as clonazepam, primidone, and levodopa was poor. In most cases, OT symptoms remain relatively unchanged over the years, but in 6 of 41 cases (15%), the condition gradually worsened over the years, and in some of these cases, symptoms spread proximally to involve the trunk and arms. OT may not be a discrete disorder as commonly believed and associated features like parkinsonism present in nearly 25% of cases. Dopaminergic dysfunction may have a role in the pathophysiology of this disorder.

Aged↗

PubMed2004

The effect of short-duration bursts of high-frequency, low-intensity transcranial magnetic stimulation on the human motor cortex.

OBJECTIVE: To explore the effect of applying a short burst of high-frequency repetitive transcranial magnetic stimulation (rTMS) to the human motor cortex as a preparatory investigation before attempting theta burst stimulation in humans. METHODS: Five or 15 pulses of 50 Hz rTMS were given at 50-80% active motor threshold (AMT). The time course of changes in motor-evoked potential (MEP) size and short interval intracortical inhibition (SICI) were evaluated from 20 to 300 ms after the end of each burst in the relaxed first dorsal interosseous muscle of 15 healthy volunteers. RESULTS: No subjects noted any adverse effects. MEPs were enhanced and SICIs were reduced at 20 ms after a burst of either 5 or 15 pulses at 70 or 80% AMT, but not at 50% AMT. Subsequent experiments used a 5 pulse burst at 80% AMT. The threshold for producing SICI increased from 60 to 80% AMT when tested 10 or 20 ms after the end of the burst. MEPs were enhanced for 100 ms, whereas SICI was reduced for 200-300 ms. CONCLUSIONS: A short burst of low-intensity 50 Hz rTMS over the hand motor area transiently increases MEP amplitude with a longer lasting decrease in SICI. SIGNIFICANCE: This means that it may be possible in future experiments to apply theta burst conditioning safely to the human cortex.

Adult↗