Margot Schubert

Treatment of tension-type headache with botulinum toxin type A: a double-blind, placebo-controlled study.

Objective.–To determine whether injections of botulinum toxin could be of therapeutic value in the treatment of tension‐type headache.

Muscle vibration: Different effects on transcranial magnetic and electrical stimulation

Transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (TES) were applied before and 3 s after onset of vibration (0.5 mm, 80 Hz) of the right extensor carpi radialis muscle in 5 healthy subjects. Vibration induced significant augmentation and latency shortening of motor evoked potentials elicited by TMS, but not TES. This provides evidence for an involvement of cortical mechanisms by muscle vibration in the augmentation of MEPs following TMS.

Modulation of motor evoked potentials by muscle vibration: The role of vibration frequency

Augmentation of motor evoked potentials (MEPs) by muscle vibration (MV) was studied in 10 healthy subjects with regard to the vibration frequency (VF). The extensor carpi radialis muscle (ECR) was vibrated using VFs of 80, 120, and 160 Hz. Motor evoked potentials following transcranial magnetic stimulation were recorded simultaneously from the vibrated ECR and the antagonist flexor carpi radialis muscle (FCR) without MV, 0.5 s and 3 s after onset of MV and 1 s after offset. Only the VFs of 80 Hz and 120 Hz caused MEP augmentation and latency shortening in ECR, whereas depression of MEPs in FCR was induced by all VFs used. It appears that MEP augmentation and latency shortening in ECR are mediated by the primary muscle spindle endings which respond with optimal discharge rates to VFs of up to 100 Hz. Motor evoked potential depression in FCR, being well expressed also with VF 160 Hz, seems to involve other dynamic mechanoreceptors.

Discharge pattern of single motor units in basal ganglia disorders

We studied the discharge pattern of motor units (MUs) from the first dorsal interosseous muscle during slight stationary isometric contraction. In six controls, seven patients with parkinsonism, and five patients with choreic disorders, we analyzed 78 MUs. About one-half of the MUs in both patient groups fired irregularly as shown by interval histograms, joint interval histograms, and corresponding statistical calculations. Cross-correlation techniques revealed a characteristic type of MU synchronization in parkinsonism. Analysis of the MU discharge pattern can be useful in clinical assessment of these disorders.

Remote F-wave changes after local botulinum toxin application.

OBJECTIVE Although the therapeutic effects of botulinum toxin A can be explained by its action at the neuromuscular junction, central or more proximal effects have also been discussed. METHODS Eleven patients with torticollis spasmodicus and 3 patients with writers cramp were studied before and 1 and 5 weeks after the first treatment with botulinum toxin. We measured compound muscle action potentials (CMAPs), motor conduction velocities (MCVs), the shortest (SFL) and the mean F-wave latencies (MFL) and F-wave persistence (30 trials) of untreated muscles for each side (ulnar nerve-abductor digiti minimi muscle, peroneal nerve-tibialis anterior muscle). RESULTS CMAPs and MCVs showed no significant changes. For both nerves, however, SFL and MFL were prolonged slightly 1 week after treatment and returned to about baseline after 5 weeks (t test). The F-wave persistence was reduced 1 week after treatment for the right ulnar and both peroneal nerves (t test). CONCLUSIONS These results are not likely due to an impairment of neuromuscular transmission. Instead, we propose a decreased excitability of alpha-motoneurons supplying non-treated muscles. A reduction of muscle spindle activity or changes of the recurrent inhibition are discussed as possible causes.

Human evoked potentials to long duration vibratory stimuli: role of muscle afferents

Tonic vibratory stimuli of 1000 ms duration and different frequencies were delivered to muscles of the forearms of young human subjects. Evoked potentials (EPs) were recorded from 29 scalp channels and revealed phasic highly lateralised and focally distributed EPs during the first 100 ms of the recording epoch that could be adequately modelled with a single point dipole source located in the vicinity of the central sulcus contralateral to the stimulated arm. A later negativity with an onset of about 400 ms and a duration of about 800 ms was found to be symmetrically distributed over fronto-central regions. This negativity is interpreted in terms of cortical activation beyond the primary sensory fields and could be related to the kinaesthetic phenomena experienced during muscle vibration.

Subthreshold prefrontal repetitive transcranial magnetic stimulation reduces motor cortex excitability

The prefrontal cortex plays an important role in central motor control. We have examined whether prefrontal repetitive transcranial magnetic stimulation (rTMS) induces changes of motor cortex excitability determined by motor evoked potentials (MEPs) following single‐pulse TMS. We studied 18 healthy volunteers stimulated at 5 Hz with 10% subthreshold prefrontal vs. occipital rTMS for 12 s. MEPs from the flexor carpi radialis muscle after single‐pulse vertex stimulation were recorded during rTMS at 0, 4, 8, and 12 s. MEP areas decreased significantly after 8 s of prefrontal rTMS (P < 0.05) but not after occipital rTMS. We conclude that rTMS of the prefrontal cortex may inhibit the primary motor areas.

Differential effects of two motor tasks on ERPs in an auditory classification task: evidence of shared cognitive resources.

The aim of the study was to assess cognitive demands and fatigue during the execution of two different motor tasks. Event-related brain potentials (ERPs) were recorded from 15 healthy subjects while they concurrently performed, (1) one of two motor tasks, and (2) a three stimulus (70% standard tones, 15% target tones, 15% novel stimuli) auditory classification task. Both motor tasks required the externally paced adduction of the right thumb with the force task requiring a precise movement (feedback given) with about 50% of maximum force output (6 s on task, 4 s rest) while the displacement task required the same precise movement with only minimal force requirements. In separate sessions, both tasks were performed for about an hour with the subjects concurrently paying attention to the auditory task with button presses required for the target stimuli. This provided a dual task situation with trade-offs in P3b amplitude as a function of difficulty of the primary (motor) task. The P3b to the auditory target stimuli was reduced during the force session compared to the displacement session, indicating that the force-task placed a higher demand on cognitive resources. No differential effect of fatigue (time on task) could be ascertained over six consecutive parts of the session. The P3a component, a putative correlate of orienting of attention, showed a rapid attenuation over time but, attesting to its automatic nature, no effect of concurrent motor task. ERP components recorded timelocked to the movements showed a marked difference between the two tasks with the displacement task giving rise to higher amplitudes. Moreover, only for the force task an influence of time on task (fatigue) on the MP was found. The dual task methodology is a potentially useful tool to disentangle cognitive and motor components of central fatigue.

Parameters of human motor unit twitches obtained by intramuscular microstimulation

Intramuscular microstimulation of motor axons was used to study twitch responses of 209 motor units (MUs) in the first dorsal interosseus muscle (FDI) of 20 normal subjects. Twitch peak force (TF), maximum rate of rise of force (MRRF), contraction time (CT) and one-half relaxation time (HRT) were determined. The distributions of TF (mean 16.0 mN, median 10.3 mN) and MRRF (mean 0.88 N s-1, median 0.66 N s-1) were skewed to the right with the majority of the values lying in the lower ranges, whereas CT (mean 63 ms, median 62 ms) and HRT (mean 61 ms, median 58 ms) were approximately normally distributed. TF was significantly correlated with MRRF, but not with CT in contrast with studies of cat gastrocnemius muscle. TF values were similar to those obtained by spike-triggered averaging in the same muscle. The method proved to be reliable and appropriate for use in patients. Examples of MU twitch parameters from three patients with chronic partial denervation of the FDI are described.

Muscle fatigue, lactate, and pyruvate in mitochondrial myopathy with progressive external ophthalmoplegia

We studied muscle fatigue and serum lactate and pyruvate levels in 20 patients with mitochondrial myopathy with progressive external ophthalmoplegia (PEO). Fatigue was assessed in the adductor pollicis muscle (AP) using a low‐intensity exercise protocol (20 min). Forces (TFs) and relaxation times of ulnar nerve evoked twitches, compound muscle action potentials (CMAPs), and maximal voluntary contractions (MVCs) were monitored. Serum lactate and pyruvate levels were independently measured at rest and after exercise on a bicycle (15 min, 30 W). Most patients showed abnormal fatigue of the AP with a reduction of TFs and MVCs and normal CMAPs. The reduced TFs were significantly correlated with lactate levels at rest (r = −0.60, P < 0.05) and less so with those after exercise (r = −0.47, P < 0.05). Pyruvate levels revealed a similar correlation although they were widely scattered. We conclude that abnormal fatigue in PEO is metabolic, is localized beyond the muscle fiber membrane, and involves the electromechanical coupling and the contractile apparatus. Serum lactate levels at rest are good predictors of fatigue in PEO.