1,721,317 research outputs found
Possible role of backpropagating action potentials in corticospinal neurons in I-wave periodicity following a TMS pulse
No full textMembrane resistance and shunting inhibition: where biophysics meets state-dependent human neurophysiology
Full text linkActivation of neurons not only changes their membrane potential and firing rate but, as a secondary action reduces membrane resistance. This loss of resistance, or increase of conductance, may be of central importance in non-invasive magnetic or electric stimulation of the human brain since electrical fields cause larger changes in transmembrane voltage in resting neurones with low membrane conductances than in active neurones with high conductance. This may explain why both the immediate and after-effects of brain stimulation are smaller or even reversed during voluntary activity compared to rest. Membrane conductance is also increased during shunting inhibition, which accompanies the classic GABAa IPSP. This short-circuits nearby EPSPs and is suggested here to contribute to the magnitude and time course of short latency intracortical inhibition (SICI) and facilitation (ICF). This article is protected by copyright. All rights reserved
Sensorimotor integration in cranial muscles tested by short- and long-latency afferent inhibition
No full textObjective: To compressively investigate sensorimotor integration in the cranial-cervical muscles in healthy adults. Methods: Short- (SAI) and long-latency afferent (LAI) inhibition were probed in the anterior digastric (AD), the depressor anguli oris (DAO) and upper trapezius (UT) muscles. A transcranial magnetic stimulation pulse over primary motor cortex was preceded by peripheral stimulation delivered to the trigeminal, facial and accessory nerves using interstimulus intervals of 15-25 ms and 100-200 ms for SAI and LAI respectively. Results: In the AD, both SAI and LAI were detected following trigeminal nerve stimulation, but not following facial nerve stimulation. In the DAO, SAI was observed only following trigeminal nerve stimulation, while LAI depended only on facial nerve stimulation, only at an intensity suprathreshold for the compound motor action potential (cMAP). In the UT we could only detect LAI following accessory nerve stimulation at an intensity suprathreshold for a cMAP. Conclusions: The results suggest that integration of sensory inputs with motor output is profoundly influenced by the type of sensory afferent involved and by the functional role played by the target muscle. Significance: Data indicate the importance of taking into account the sensory receptors involved as well as the function of the target muscle when studying sensorimotor integration, both in physiological and neurological conditions
Effect of transcranial DC sensorimotor cortex stimulation on somatosensory evoked potentials in humans
No full textObjective: To study the after-effect of transcranial direct current stimulation (tDCS) over the sensorimotor cortex on the size of somatosensory evoked potentials (SEPs) in humans. Methods: SEPs were elicited by electrical stimulation of right or left median nerve at the wrist before and after anodal or cathodal tDCS in 8 healthy subjects. tDCS was applied for 10 min to the left motor cortex at a current strength of 1 mA. Results: Amplitudes of P25/N33, N33/P40 (parietal components) and P22/N30 (frontal component) following right median nerve stimulation were significantly increased for at least 60 min after the end of anodal tDCS, whereas P14/N20, N20/P25 (parietal components) and N18/P22 (frontal component) were unaffected. There was no effect on SEPs evoked by left median nerve stimulation. Cathodal tDCS had no effect on SEPs evoked from stimulation of either arm. Conclusions: Anodal tDCS over the sensorimotor cortex can induce a long-lasting increase in the size of ipsilateral cortical components of SEPs. Significance: tDCS can modulate cortical somatosensory processing in humans and might be a useful tool to induce plasticity in cortical sensory processing. (C) 2003 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved
Physiological differences in hand and face areas of the primary motor cortex in skilled wind and string musicians
No full textThe process of learning and playing a musical instrument modulates the structural and functional organization of cortical motor networks. In the present study the excitability and short-term functional plasticity of face and hand areas of primary motor cortex (M1) were compared in woodwind musicians (WM), string musicians (SM) and non-musicians to test the hypothesis that neurophysiological adaptations to the long-term experience of playing a musical instrument are site-specific and related to the particular physiological properties of the representation area in M1. Twenty-two musicians (11 SM, 11 WM) and 11 non-musicians participated in the study. Transcranial magnetic stimulation (TMS) was used to probe rest and active short-latency intracortical inhibition (SICI), interhemispheric inhibition (IHI) and response to paired associative stimulation (PAS). TMS-induced motor evoked potentials (MEP) were recorded from the depressor anguli oris (DAO) and the first dorsal interosseous (FDI) muscles, respectively. Rest and active SICI were the same in all groups (all p>0.05). WM exhibited significant IHI in the DAO (p=0.031), in contrast to its absence in SM and non-musicians. Compared with non-musicians and WM, the PAS-induced increase in MEP amplitude in SM was significantly larger in hand M1 (p=0.008) but not in face M1. In conclusion, neurophysiological adaptations differ between WM, in whom control of the embouchure is highly important, and SM who perform a large range of sequential finger movements and are site-specific in M1
Frequency-dependent modulation of cerebellar excitability during the application of non-invasive alternating current stimulation
Full text linkBACKGROUND: it is well-known that the cerebellum is critical for the integrity of motor and cognitive actions. Applying non-invasive brain stimulation techniques over this region results in neurophysiological and behavioural changes, which have been associated with the modulation of cerebellar-cerebral cortex connectivity. Here, we investigated whether online application of cerebellar transcranial alternating current stimulation (tACS) results in changes to this pathway. METHODS: thirteen healthy individuals participated in two sessions of cerebellar tACS delivered at different frequencies (5Hz and 50Hz). We used transcranial magnetic stimulation to measure cerebellar-motor cortex (M1) inhibition (CBI), short-intracortical inhibition (SICI) and short-afferent inhibition (SAI) before, during and after the application of tACS. RESULTS: we found that CBI was specifically strengthened during the application of 5Hz cerebellar tACS. No changes were detected immediately following the application of 5Hz stimulation, nor at any time point with 50Hz stimulation. We also found no changes to M1 intracortical circuits (i.e. SICI) or sensorimotor interaction (i.e. SAI), indicating that the effects of 5Hz tACS over the cerebellum are site-specific. CONCLUSIONS: cerebellar tACS can modulate cerebellar excitability in a time- and frequency-dependent manner. Additionally, cerebellar tACS does not appear to induce any long-lasting effects (i.e. plasticity), suggesting that stimulation enhances oscillations within the cerebellum only throughout the stimulation period. As such, cerebellar tACS may have significant implications for diseases manifesting with abnormal cerebellar oscillatory activity and also for future behavioural studies
Effects of 10Hz and 20Hz transcranial alternating current stimulation on automatic motor control
No full textpeer reviewedBackground: Automatic motor inhibition is an important and adaptive process through which an activated motor plan is suppressed if the movement is not intended to be executed. Neuronal networks are characterized by oscillatory activity. In the brain, a large variety of rhythms have been described that differ in their frequency, origin and reactivity to changes in task demands. Recent studies have demonstrated that active cortical networks are susceptible to weak sinusoidal perturbations of exogenous electric fields.
Objective/Hypothesis: The aim of this study was to investigate the frequency-specific effect of
transcranial alternate current stimulation (tACS) over the automatic control of movement in healthy volunteers. We hypothesized that applying two different tACS frequencies during a visuo-motor
task would result in different behavioural effects and in diverse modulation of cortical excitability.
Methods: In this study we used tACS to interact non-invasively with the ongoing task-related
oscillatory activity. Stimulation was delivered at alpha (10 Hz) and beta (20 Hz) frequency over the
supplementary motor area and the primary motor cortex (SMA-M1) connections, which are part of
the BG-cortical motor loop, during the execution of the subliminal masked prime task. We measured the effects on task performance and on motor cortex corticospinal excitability by means of motor evoked potentials (MEPs) evoked by transcranial magnetic stimulation (TMS).
Results: Results indicate a specific effect of 10 and 20-Hz tACS on functional inhibition in the
SMA-M1 circuit. Behaviorally there is an interference in task-related automatic inhibition: 10 Hz tACS reduced the automatic inhibition. In contrast 20 Hz tACS increased the automatic inhibition.
At a neurophysiological level there is a modulation in excitability of M1: 20 Hz tACS reduced MEP amplitudes, whereas there was no change after 10 Hz tACS.
Conclusion(s): The current study provides novel evidence that automatic mechanisms of motor
behaviour can be modulated by imposing synchronized electrical oscillatory activity upon motor
cortical regions. Our study has important implications for cognitive neuroscience studies
suggesting that the use tACS might offer the possibility to demonstrate a causal link between
endogenous brain oscillations, specific exogenous alternate current frequencies and specific
cognitive processes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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