Joachim Liepert

Repeated premotor rTMS leads to cumulative plastic changes of motor cortex excitability in humans

We explored the aftereffects of two premotor 1 Hz rTMS sessions on motor cortex excitability in healthy humans. In experiment 1, 11 healthy right-handed volunteers received 20-min submotor threshold 1 Hz rTMS trains over the left premotor cortex on 2 consecutive days. Left motor cortex excitability was determined at baseline, immediately after, 30, 60, 120 min, and 24 h after each rTMS session. We measured motor thresholds, amplitudes of motor-evoked potentials, silent periods, and paired-pulse excitability at interstimulus intervals (ISI) of 3-7, 10, and 15 ms. In experiment 2, 5 volunteers received two identical rTMS trains on Days 1 and 7. Measurements were carried out on Day 1 (first rTMS train), Day 2, and Day 7 (second rTMS train). In experiment 1 there was a selective increase of paired pulse facilitation at an ISI of 7 ms after rTMS lasting for less than 30 min on Day 1. This effect was also present after rTMS on Day 2. However, it persisted for at least 2 h. In experiment 2 the same extra facilitation was induced by rTMS on Days 1 and 7 but not on Day 2. It lasted for less than 30 min on both Day 1 and Day 7. We conclude that 1 Hz premotor rTMS leads to cumulative plastic changes of intrinsic motor cortex excitability when repeated within 24 h but not after 1 week, implying the formation of memory after the first rTMS train lasting more than a day but less than a week.

Abnormal plasticity of the sensorimotor cortex to slow repetitive transcranial magnetic stimulation in patients with writer's cramp

Previous studies demonstrated functional abnormalities in the somatosensory system, including a distorted functional organization of the somatosensory cortex (S1) in patients with writers cramp. We tested the hypothesis that these functional alterations render S1 of these patients more susceptible to the “inhibitory” effects of subthreshold 1 Hz repetitive transcranial magnetic stimulation (rTMS) given to S1. Seven patients with writers cramp and eight healthy subjects were studied. Patients also received rTMS to the motor cortex hand area (M1). As an outcome measure, short‐latency afferent inhibition (SAI) was tested. SAI was studied in the relaxed first dorsal interosseous muscle using conditioning electrical stimulation of the index finger and TMS pulses over the contralateral M1. Baseline SAI did not differ between groups. S1 but not M1 rTMS reduced SAI in patients. rTMS had no effects on SAI in healthy subjects. Because SAI is mediated predominantly at a cortical level in the sensorimotor cortex, we conclude that there is an abnormal responsiveness of this area to 1 Hz rTMS in writers cramp, which may represent a trait toward maladaptive plasticity in the sensorimotor system in these patients.

Fatigue suppresses ipsilateral intracortical facilitation

Experimental data in animals and humans have demonstrated connections between right and left motor cortices. Interactions between these cortical areas can be explored with electrical or magnetic stimulation. In the present study we examined the interhemispheric effect of fatigue on intracortical facilitation (ICF) and inhibition (ICI) using a paired-pulse transcranial magnetic stimulation (TMS) paradigm. Ten healthy subjects performed pinch grips with their left hand with 50% maximum voluntary contraction (MVC) until fatigue occurred. In the control experiment, the same number of pinch grips was performed with 5% MVC without inducing fatigue. Motor evoked potentials (MEP) produced by single and paired pulse TMS over the left motor cortex were recorded from right first dorsal interosseous muscle (FDI) and right abductor digiti minimi muscle (ADM) before and after the tasks. ICF of the right FDI was significantly reduced after fatigue (P=0.0008). Fifteen minutes after finishing the task ICF had returned to baseline values. There was no change of ICF of right FDI in the control experiment without inducing fatigue. In both experiments the right ADM did not show significant MEP changes. Additional control experiments showed that M-responses and F-waves were unchanged in right FDI after performing the fatigue task with left FDI, and TMS test pulse amplitudes were significantly reduced in left FDI after fatigue. Fatigue caused by pinch grips induces a short-lasting and task-specific suppression of intracortical facilitation in the motor cortex of an homologous contralateral hand muscle. These results indicate interhemispheric interactions between the two motor cortices that are still effective after cessation of movements.

Motor excitability in a patient with a somatosensory cortex lesion

OBJECTIVE We report a patient with an ischemic lesion in right somatosensory cortex who developed dystonic posturing and pseudo-athetotic involuntary left-sided finger movements during voluntary muscle contractions. METHODS Motor excitability was assessed using transcranial magnetic stimulation techniques and electrical peripheral nerve stimulation. Results obtained from abductor digiti minimi muscles of both hands were compared. RESULTS On the affected side, silent period duration and intracortical inhibition were reduced, indicating a loss of inhibitory properties. Intracortical facilitation was enhanced. Stimulus-response curves showed a smaller increase of motor evoked potential amplitudes when recorded during muscle relaxation, but not during voluntary muscle activation. CONCLUSIONS The results suggest that, under normal conditions, somatosensory cortex modifies inhibitory as well as excitatory properties in the motor system.

Motor excitability in myopathy

OBJECTIVE To explore whether patients with myopathy present changes in motoneuronal excitability. METHODS Patients with well-defined myopathies were studied with single and paired pulse transcranial magnetic stimulations and electrical nerve stimulations to explore neuronal motor excitability. Motor-evoked potentials were recorded from the clinically unaffected first dorsal interosseous muscle (n=10) and the paretic deltoid muscle (n=8). RESULTS Compared to an age-matched healthy control group, myopathic patients showed a reduction of intracortical inhibition, enhancements of alpha-motoneuron excitability and increased amplitudes of motor-evoked potentials during target muscle contraction. These alterations were present in clinically affected and clinically unaffected muscles. CONCLUSION In myopathy, nervous system excitability may be altered, presenting as a motor disinhibition on cortical and subcortical levels.

Chapter 37 TMS in stroke

Publisher Summary Transcranial magnetic stimulation (TMS) in stroke is useful for several reasons, such as TMS in the early stage after stroke provides important prognostic informations, TMS helps to quantify the severity of central motor pathway lesions, and TMS serves to describe motor excitability changes associated with spontaneous or therapy-induced improvement of motor functions. This chapter discusses different indications for TMS after stroke and the information that can be obtained by the use of various TMS techniques. Various TMS techniques have demonstrated perilesional excitability changes. They further support the hypothesis that a single monohemispheric lesion may affect a widespread bihemispherically-organized network. TMS methods have also shown that the adult brain is capable of reorganization, and appropriately- timed TMS pulses can help to clarify the functional relevance of brain areas activated in positron emission tomography (PET) or functional magnetic resonance imaging (fMRI) studies.

Shall I Move My Right or My Left Hand

Abstract Event-related desynchronization/synchronization (ERD/ERS) at alpha (10Hz), beta (20Hz), and gamma (40Hz) bands and movement-related potentials (MRPs) were investigated in right-handed subjects who were “free” to decide the side of unilateral finger movements (“fixed” side as a control). As a novelty, this “multi-modal” EEG analysis was combined with the evaluation of involuntary mirror movements, taken as an index of “bimanual competition.” A main issue was whether the decision regarding the hand to be moved (“free” movements) could modulate ERD/ERS or MRPs overlying sensorimotor cortical areas typically involved in bimanual tasks. Compared to “fixed” movements, “free” movements induced the following effects: (1) more involuntary mirror movements discarded from EEG analysis; (2) stronger vertex MRPs (right motor acts); (3) a positive correlation between these potentials and the number of involuntary mirror movements; (4) gamma ERS over central areas; and (5) preponderance of postmovement beta ERS...

Funktionelle Bildgebung in der Neurorehabilitation

Es ist vielleicht gerechtfertigt zu sagen, dass die Befunde der funktionellen Bildgebung der letzten 10 Jahre bei Schlaganfallpatienten viele Gedanken der Rehabilitation auf eine neue neurobiologische Basis gestellt haben und dadurch der Rehabilitation Schwung, Interesse und neuen Enthusiasmus gebracht haben und auch Wege aufgezeigt haben, wie rehabilitative Techniken auf neurobiologischer Basis evaluiert werden konnten. Man versteht besser, was im Gehirn eines Schlaganfallpatienten vorgeht. Man »sieht« den ipsilateralen Kortex aufblitzen, wenn Mitbewegungen der gesunden Seite bei der Visite zu beobachten sind und kann vielleicht die Ruckbildung der Diaschisis vermuten, wenn sich die Sprache innerhalb der ersten Woche plotzlich von einem auf den anderen Tag deutlich bessert. Gerade erst scheint die Zeit zu beginnen, in der Messungen am Patienten eine konkrete Anpassung der Behandlung bringen.