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Short-interval Intracortical Inhibition (short-interval + intracortical_inhibition)
Selected AbstractsPregabalin Exerts Oppositional Effects on Different Inhibitory Circuits in Human Motor Cortex: A Double-blind, Placebo-controlled Transcranial Magnetic Stimulation StudyEPILEPSIA, Issue 5 2006Nicolas Lang Summary:,Purpose: To explore acute effects of pregabalin (PGB) on human motor cortex excitability with transcranial magnetic stimulation (TMS). Methods: PGB, 600 mg/day, was orally administered in 19 healthy subjects twice daily in a randomized, double-blind, placebo-controlled crossover design. Several measures of motor cortex excitability were tested with single- and paired-pulse TMS. Results: Mean short-interval intracortical inhibition (SICI) was reduced after PGB (74 ± 7% of unconditioned response) compared with placebo (60 ± 6% of unconditioned response). In contrast, mean long-interval intracortical inhibition (LICI) was increased by PGB (26 ± 4% of unconditioned response) compared with placebo (45 ± 8% of unconditioned response), and mean cortical silent period (CSP) showed an increase from 139 ± 8 ms or 145 ± 8 ms after placebo to 162 ± 7 ms or 161 ± 10 ms after PGB. Motor thresholds, intracortical facilitation, and corticospinal excitability were unaffected. Conclusions: The observed excitability changes with oppositional effects on SICI and LICI or CSP suggest ,-aminobutyric acid (GABA)B -receptor activation. They are markedly distinct from those induced by gabapentin, although both PGB and gabapentin are thought to mediate their function by binding to the ,(2)-, subunit of voltage-gated calcium channels. Conversely, the TMS profile of PGB shows striking similarities with the pattern evoked by the GABA-reuptake inhibitor tiagabine. [source] Differences between the effects of three plasticity inducing protocols on the organization of the human motor cortexEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2006Karin Rosenkranz Abstract Several experimental protocols induce lasting changes in the excitability of motor cortex. Some involve direct cortical stimulation, others activate the somatosensory system and some combine motor and sensory stimulation. The effects usually are measured as changes in amplitude of the motor-evoked-potential (MEP) or short-interval intracortical inhibition (SICI) elicited by a single or paired pulses of transcranial magnetic stimulation (TMS). Recent work has also tested sensorimotor organization within the motor cortex by recording MEPs and SICI during short periods of vibration applied to single intrinsic hand muscles. Here sensorimotor organization is focal: MEPs increase and SICI decreases in the vibrated muscle, whilst the opposite occurs in neighbouring muscles. In six volunteers we compared the after effects of three protocols that lead to lasting changes in cortical excitability: (i) paired associative stimulation (PAS) between a TMS pulse and an electrical stimulus to the median nerve; (ii) motor practice of rapid thumb abduction; and (iii) sensory input produced by semicontinuous muscle vibration, on MEPs and SICI at rest and on the sensorimotor organization. PAS increased MEP amplitudes, whereas vibration changed sensorimotor organization. Motor practice had a dual effect and increased MEPs as well as affecting sensorimotor organization. The implication is that different protocols target different sets of cortical circuits. We speculate that protocols that involve repeated activation of motor cortical output lead to lasting changes in efficacy of synaptic connections in output circuits, whereas protocols that emphasize sensory inputs affect the strength of sensory inputs to motor circuits. [source] Decreased cortical inhibition and yet cerebellar pathology in ,familial cortical myoclonic tremor with epilepsy'MOVEMENT DISORDERS, Issue 16 2007Anne-Fleur van Rootselaar MD Abstract Cortical hyperexcitability is a feature of "familial cortical myoclonic tremor with epilepsy" (FCMTE). However, neuropathological investigations in a single FCMTE patient showed isolated cerebellar pathology. Pathological investigations in a second FCMTE patient, reported here, confirmed cerebellar Purkinje cell degeneration and a normal sensorimotor cortex. Subsequently, we sought to explore the nature of cerebellar and motor system pathophysiology in FCMTE. Eye movement recordings and transcranial magnetic stimulation performed in six related FCMTE patients showed impaired saccades and smooth pursuit and downbeat nystagmus upon hyperventilation, as in patients with spinocerebellar ataxia type 6. In FCMTE patients short-interval intracortical inhibition (SICI) was significantly reduced. Resting motor threshold, recruitment curve, silent period, and intracortical facilitation were normal. The neuropathological and ocular motor abnormalities indicate cerebellar involvement in FCMTE patients. Decreased SICI is compatible with intracortical GABAA -ergic dysfunction. Cerebellar and intracortical functional changes could result from a common mechanism such as a channelopathy. Alternatively, decreased cortical inhibition may be caused by dysfunction of the cerebello-thalamo-cortical loop as a result of primary cerebellar pathology. © 2007 Movement Disorder Society [source] Mechanisms underlying mirror movements in Parkinson's disease: A transcranial magnetic stimulation studyMOVEMENT DISORDERS, Issue 7 2006Massimo Cincotta MD Abstract The neural mechanisms underlying unintended mirror movements (MMs) of one hand during unimanual movements of the other hand in patients with Parkinson's disease (PD) are largely unexplored. Here we used surface electromyographic (EMG) analysis and focal transcranial magnetic stimulation (TMS) to investigate the pathophysiological substrate of MMs in four PD patients. Surface EMG was recorded from both abductor pollicis brevis (APB) and first dorsal interosseous (FDI) muscles. Cross-correlation EMG analysis revealed no common motor drive to the two APBs during intended unimanual tasks. Focal TMS of either primary motor cortex (M1) elicited normal motor-evoked potentials (MEPs) in the contralateral APB, whereas MEPs were not seen in the ipsilateral hand. During either mirror or voluntary APB contraction, focal TMS of the contralateral M1 produced a long-lasting silent period (SP), whereas stimulation of the ipsilateral M1 produced a short-lasting SP. During either mirror or voluntary finger tapping, 5 Hz repetitive TMS (rTMS) of the contralateral M1 disrupted EMG activity in the target FDI, whereas the effects of rTMS of the ipsilateral M1 were by far slighter. During either mirror or voluntary APB contraction, paired-pulse TMS showed a reduction of short-interval intracortical inhibition in the contralateral M1. These findings provide converging evidence that, in PD, MMs do not depend on unmasking of ipsilateral projections but are explained by motor output along the crossed corticospinal projection from the mirror M1. © 2006 Movement Disorder Society [source] Dissociated effects of diazepam and lorazepam on short-latency afferent inhibitionTHE JOURNAL OF PHYSIOLOGY, Issue 1 2005Vincenzo Di Lazzaro Peripheral nerve inputs have an inhibitory effect on motor cortex excitability at short intervals (short-latency afferent inhibition, SAI). This can be tested by coupling electrical stimulation of peripheral nerve with transcranial magnetic stimulation (TMS) of the motor cortex. SAI is reduced by the anticholinergic drug scopolamine, and in patients with Alzheimer's disease. Therefore, it is possible that SAI is a marker of central cholinergic activity important for memory function. The benzodiazepine lorazepam also reduces SAI. Since benzodiazepines impair memory formation, but do not do so uniformly, with a maximum amnesic effect after lorazepam but less or no effect after diazepam, we were interested in testing in this non-behavioural study to what extent the effects of lorazepam and diazepam on circuits involved in SAI could be dissociated. In addition, and for control, we tested the effects of lorazepam and diazepam on short-interval intracortical inhibition (SICI), a motor cortical inhibition mediated through the GABAA receptor. Lorazepam markedly reduced SAI, whereas diazepam slightly increased it. In contrast, both benzodiazepines uniformly increased SICI. Our findings demonstrate opposite effects of lorazepam and diazepam on SAI, an inhibition modulated by central cholinergic activity, but the same effects on SICI, a marker of neurotransmission through the GABAA receptor. This dissociation suggests, for the first time, that TMS measures of cortical inhibition provide the opportunity to segregate differences of benzodiazepine action in human central nervous system circuits. [source] Interhemispheric interaction between human dorsal premotor and contralateral primary motor cortexTHE JOURNAL OF PHYSIOLOGY, Issue 1 2004Hitoshi Mochizuki 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. [source] | |||||||||||||