The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Cornelius Weiller - One of the best experts on this subject based on the ideXlab platform.
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Motor Cortex excitability after thalamic infarction.
Clinical Neurophysiology, 2005Co-Authors: Joachim Liepert, C. Restemeyer, Alexander Münchau, Cornelius WeillerAbstract:Abstract Objective We examined 8 patients with hemihypesthesia due to an ischemic thalamic lesion to explore the effects of a central sensory dysfunction on Motor Cortex excitability. Methods Motor excitability was assessed using transcranial magnetic stimulation techniques and electrical peripheral nerve stimulation. Motor function was evaluated by the Nine-Hole-Peg Test and measurement of hand grip strength. The affected side was compared with the non-lesioned side and with an age-matched control group. Results Patients had a loss of inhibition and an increase of facilitation in the Motor Cortex of the affected side. The silent period was prolonged and Motor function was impaired on the affected side. Conclusions A thalamic lesion can modulate Motor cortical excitability. Significance This study suggests that, under normal conditions, somatosensory afferents influence inhibitory and excitatory properties in the Motor Cortex.
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Motor Cortex disinhibition in Alzheimer's disease
Clinical Neurophysiology, 2001Co-Authors: Joachim Liepert, U. Meske, Cornelius WeillerAbstract:Abstract Objectives : To explore subclinical disturbances in the Motor Cortex of patients with Alzheimer's disease (AD). Methods : We used transcranial magnetic stimulation in a paired pulse technique to test intracortical inhibition (ICI) and intracortical facilitation in mildly to moderately demented AD patients with a normal neurological examination. Patients were studied before and during treatment with the cholinesterase inhibitor donepezil. Results : AD patients had a reduced ICI compared to an age-matched control group. The amount of disinhibition correlated with the severity of dementia. Treatment with 10 mg donepezil daily was associated with an increase of ICI. Conclusions : The subclinical Motor Cortex disinhibition in AD patients indicates a functional disturbance, and is probably associated with a cholinergic deficit.
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Motor Cortex disinhibition in acute stroke
Clinical Neurophysiology, 2000Co-Authors: Joachim Liepert, P Storch, Andreas Fritsch, Cornelius WeillerAbstract:Abstract Objectives : To test whether a disinhibition occurs in the human Motor Cortex after stroke. Methods : Patients with a mild to moderate hemiparesis after an acute unilateral ischemic stroke were compared with age-matched healthy controls. We used paired transcranial magnetic stimuli (TMS) to investigate intracortical inhibition and facilitation. Single TMS were applied to obtain a cortical silent period. Results : Intracortical inhibition was significantly reduced in the affected hemisphere at interstimulus intervals of 2, 3 and 4 ms. The cortical silent period was significantly prolonged when compared to the unaffected hemisphere of the patients and to the control group. Motor Cortex disinhibition observed in stroke patients was associated either with minimal impairment at the onset of symptoms or with rapidly improving Motor functions. Conclusions : Motor Cortex disinhibition occurs in humans after stroke. We suggest that this disinhibition is indicative of compensatory mechanisms, which are involved in recovery-related reorganization.
Joachim Liepert - One of the best experts on this subject based on the ideXlab platform.
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Motor Cortex excitability after thalamic infarction.
Clinical Neurophysiology, 2005Co-Authors: Joachim Liepert, C. Restemeyer, Alexander Münchau, Cornelius WeillerAbstract:Abstract Objective We examined 8 patients with hemihypesthesia due to an ischemic thalamic lesion to explore the effects of a central sensory dysfunction on Motor Cortex excitability. Methods Motor excitability was assessed using transcranial magnetic stimulation techniques and electrical peripheral nerve stimulation. Motor function was evaluated by the Nine-Hole-Peg Test and measurement of hand grip strength. The affected side was compared with the non-lesioned side and with an age-matched control group. Results Patients had a loss of inhibition and an increase of facilitation in the Motor Cortex of the affected side. The silent period was prolonged and Motor function was impaired on the affected side. Conclusions A thalamic lesion can modulate Motor cortical excitability. Significance This study suggests that, under normal conditions, somatosensory afferents influence inhibitory and excitatory properties in the Motor Cortex.
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Motor Cortex disinhibition in Alzheimer's disease
Clinical Neurophysiology, 2001Co-Authors: Joachim Liepert, U. Meske, Cornelius WeillerAbstract:Abstract Objectives : To explore subclinical disturbances in the Motor Cortex of patients with Alzheimer's disease (AD). Methods : We used transcranial magnetic stimulation in a paired pulse technique to test intracortical inhibition (ICI) and intracortical facilitation in mildly to moderately demented AD patients with a normal neurological examination. Patients were studied before and during treatment with the cholinesterase inhibitor donepezil. Results : AD patients had a reduced ICI compared to an age-matched control group. The amount of disinhibition correlated with the severity of dementia. Treatment with 10 mg donepezil daily was associated with an increase of ICI. Conclusions : The subclinical Motor Cortex disinhibition in AD patients indicates a functional disturbance, and is probably associated with a cholinergic deficit.
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Motor Cortex disinhibition in acute stroke
Clinical Neurophysiology, 2000Co-Authors: Joachim Liepert, P Storch, Andreas Fritsch, Cornelius WeillerAbstract:Abstract Objectives : To test whether a disinhibition occurs in the human Motor Cortex after stroke. Methods : Patients with a mild to moderate hemiparesis after an acute unilateral ischemic stroke were compared with age-matched healthy controls. We used paired transcranial magnetic stimuli (TMS) to investigate intracortical inhibition and facilitation. Single TMS were applied to obtain a cortical silent period. Results : Intracortical inhibition was significantly reduced in the affected hemisphere at interstimulus intervals of 2, 3 and 4 ms. The cortical silent period was significantly prolonged when compared to the unaffected hemisphere of the patients and to the control group. Motor Cortex disinhibition observed in stroke patients was associated either with minimal impairment at the onset of symptoms or with rapidly improving Motor functions. Conclusions : Motor Cortex disinhibition occurs in humans after stroke. We suggest that this disinhibition is indicative of compensatory mechanisms, which are involved in recovery-related reorganization.
Ulf Ziemann - One of the best experts on this subject based on the ideXlab platform.
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LTP-like plasticity in human Motor Cortex.
Supplements to Clinical neurophysiology, 2020Co-Authors: Ulf ZiemannAbstract:Publisher Summary This chapter discusses some of the recent developments in the field of transcranial magnetic stimulation (TMS), which provided several lines of evidence regarding TMS inducing long-term potentiation (LTP)-like plasticity in human Motor Cortex. For cooperativity of plasticity induced by repetitive transcranial magnetic stimulation, six healthy subjects were tested in three different experimental manipulations––namely, repetitive transcranial magnetic stimulation (rTMS), ischemic nerve block (INB), and rTMS during INB (rTMS+INB). The findings strongly suggest the presence of cooperativity in (rTMS + INB) the model of plasticity in human Motor Cortex as low-rate rTMS was capable of producing a long-lasting enhancement of the Motor Cortex biceps representation only when the threshold of induction was lowered by the INB-induced reduction of gamma-aminobutyric acid (GABA) in the stimulated Motor Cortex. For the input-specificity of plasticity induced by repetitive transcranial magnetic stimulation, six healthy subjects were tested in six different experimental conditions. The findings of this study demonstrate that the long-lasting enhancement of the arm representation is input-specific as this enhancement was induced only when the arm representation was effectively stimulated by rTMS.
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I-waves in Motor Cortex revisited
Experimental Brain Research, 2020Co-Authors: Ulf ZiemannAbstract:I-waves represent high-frequency (~ 600 Hz) repetitive discharge of corticospinal fibers elicited by single-pulse stimulation of Motor Cortex. First detected and examined in animal preparations, this multiple discharge can also be recorded in humans from the corticospinal tract with epidural spinal electrodes. The exact underpinning neurophysiology of I-waves is still unclear, but there is converging evidence that they originate at the cortical level through synaptic input from specific excitatory interneuronal circuitries onto corticomotoneuronal cells, controlled by GABAAergic interneurons. In contrast, there is at present no supportive evidence for the alternative hypothesis that I-waves are generated by high-frequency oscillations of the membrane potential of corticomotoneuronal cells upon initial strong depolarization. Understanding I-wave physiology is essential for understanding how TMS activates the Motor Cortex.
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I-waves in Motor Cortex.
Journal of Clinical Neurophysiology, 2000Co-Authors: Ulf Ziemann, John C. RothwellAbstract:I-waves refer to high-frequency (approximately 600 Hz) repetitive discharge of corticospinal fibers produced by single-pulse stimulation of the Motor Cortex. First detected in animal preparations, this multiple discharge can also be recorded in humans with epidural electrodes over the spinal cord, and with recently developed noninvasive paired-pulse transcranial magnetic stimulation protocols. The exact nature of the generation of I-waves is still unclear, but there is convincing evidence that they originate in the Motor Cortex, mainly through activation of corticocortical projections onto corticospinal neurons. The ability to measure I-waves in human Motor Cortex allows one to test the integrity and excitability of the underlying corticocortical circuits in health and disease.
Nicholas G. Hatsopoulos - One of the best experts on this subject based on the ideXlab platform.
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Perspectives on classical controversies about the Motor Cortex.
Journal of Neurophysiology, 2017Co-Authors: Mohsen Omrani, Nicholas G. Hatsopoulos, Matthew T. Kaufman, Paul D. CheneyAbstract:Primary Motor Cortex has been studied for more than a century, yet a consensus on its functional contribution to movement control is still out of reach. In particular, there remains controversy as to the level of control produced by Motor Cortex (“low-level” movement dynamics vs. “high-level” movement kinematics) and the role of sensory feedback. In this review, we present different perspectives on the two following questions: What does activity in Motor Cortex reflect? and How do planned Motor commands interact with incoming sensory feedback during movement? The four authors each present their independent views on how they think the primary Motor Cortex (M1) controls movement. At the end, we present a dialogue in which the authors synthesize their views and suggest possibilities for moving the field forward. While there is not yet a consensus on the role of M1 or sensory feedback in the control of upper limb movements, such dialogues are essential to take us closer to one.
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Motor Cortex microcircuits
Frontiers in Neural Circuits, 2013Co-Authors: Michael Brecht, Nicholas G. Hatsopoulos, Takeshi Kaneko, Gordon M. ShepherdAbstract:The goal of this Research Topic was to bring together articles representing the spectrum of current research aimed at understanding the functional organization Motor Cortex at the level of microcircuits. The original research articles in this collection address a wide range of aspects of Motor Cortex microcircuits. The monkey's Motor Cortex is an especially important model system because of the similarities to the human brain, and the ability to train monkeys to perform complex movements. However, information about the cellular composition of different primates has been limited; Young et al. (2013) now describe the cell densities in Motor Cortex across multiple primate species. Studying reaching and grasping is a powerful approach to understanding complex movements in monkeys. Riehle et al. (2013) describe the spatio-temporal structure of Motor cortical local field potentials and spiking activities during reach-to-grasp movements. Dickey et al. (2013) report on the heterogeneity of signals detected as monkeys make corrective movements while reaching. Motor cortical influences on lower limb function are also crucial for many types of Motor behavior, and Hudson et al. (2013) report new findings of differences in the cortical output to fast and slow muscles of the ankle. The rodent Motor Cortex offers a complementary model system providing more immediate access to identified cells and circuits using optogenetic and related tools. In rats, Tanaka et al. (2011) dissect the local connectivity of corticospinal neurons with different classes of interneurons. Smith and Alloway (2013) show that the whisker Motor Cortex has distinct sensory-input and Motor-output sub-regions. Applying optogenetic tools in mice, Hira et al. (2013) characterize the synaptic connectivity between rostral and caudal sub-regions encoding the forelimb representation. Studying genetically labeled pyramidal neurons in layer 5, Yu et al. (2008) demonstrate cell-type-specific local circuits and firing patterns. Also examining firing patterns, Hedrick and Waters (2012) report on their high sensitivity to temperature. The review-type articles provide new syntheses of current knowledge about different aspects of Motor Cortex function and dysfunction. Kaneko (2013) focuses on microcircuits of excitatory neurons in the rodent Motor Cortex, and develops novel concepts about the organization of thalamic innervation to Motor Cortex microcircuits. Tsubo et al. (2013) assess current knowledge about in vivo dynamic activity across Motor cortical layers in relation to movement. Harrison and Murphy (2012) emphasize the significance of particular classes of projection neurons and how these may be investigated with optogenetic strategies to determine their roles in Motor function. Capaday et al. (2013) address the functional organization of the Motor Cortex from the perspective of intracortical connectivity. Castro-Alamancos (2013) discusses how Motor Cortex operates as a dynamic, frequency-tuned, oscillating network. Mahan and Georgopoulos (2013) review directional tuning from the perspective of resonance and the role of inhibitory mechanisms. Di Lazzaro and Ziemann (2013) review evidence, gathered from transcranial magnetic stimulation studies, for the roles of different types of microcircuits in the functions of human Motor Cortex. Diseases of the Motor Cortex have devastating consequences for Motor control; Estrada-Sanchez and Rebec (2013) review the state of research on Motor cortical involvement in Huntington's disease. We are impressed not only with the diversity of contributions included here, but even more so we were delighted that researchers from all walks of Motor Cortex investigation enthusiastically steered their research toward the microcircuit theme pursued in this volume. More than ever it seems clear that we all are working toward a common goal, i.e., describing Motor cortical function in terms of the transactions in identified cellular circuits. We thank the authors for their contributions, and are additionally grateful to the many reviewers who contributed their efforts.
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Sensing with the Motor Cortex
Neuron, 2011Co-Authors: Nicholas G. Hatsopoulos, Aaron J. SuminskiAbstract:The primary Motor Cortex is a critical node in the network of brain regions responsible for voluntary Motor behavior. It has been less appreciated, however, that the Motor Cortex exhibits sensory responses in a variety of modalities including vision and somatosensation. We review current work that emphasizes the heterogeneity in sensoriMotor responses in the Motor Cortex and focus on its implications for cortical control of movement as well as for brain-machine interface development.
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Columnar organization in the Motor Cortex.
Cortex, 2009Co-Authors: Nicholas G. HatsopoulosAbstract:Despite many attempts to find spatial structure in the functional properties of neurons within the primary Motor Cortex (MI), there is still no compelling evidence for such structure despite the anatomical similarities between Motor Cortex and other neocortical areas. This is a longstanding puzzle in Motor cortical physiology because topographic structure of function is a hallmark of primary sensory cortices including the visual, somatosensory, and auditory cortices. In particular, experimental evidence has supported the idea of vertical columns perpendicular to the cortical surface which contain neurons that share similar sensory tuning properties. Moreover, horizontal spatial structure has been observed in sensory cortices, most elegantly manifested by the pinwheel structure of orientation tuning across V1 (Bonhoeffer and Grinvald, 1991). Although early work by Asanuma provided some evidence for somatotopic, columnar organization in MI using intracortical microstimulation (Asanuma, 1975), further research by many others did not support this perspective but rather suggested distributed and overlapping representations of body parts. Namely, nearby sites in Motor Cortex could represent or evoke very different muscles and joints, and multiple, spatially-distributed sites could represent very similar body parts (Donoghue, Leibovic et al., 1992; Schieber and Hibbard, 1993; Sanes, Donoghue et al., 1995). By focusing on movement parameters instead of body parts, recent studies have provided evidence that a topographic organization of directional tuning does exist within the Motor Cortex (Amirikian and Georgopoulos, 2003; Georgopoulos, Merchant et al., 2007). However, it still remains controversial as to which movement parameters, if any, are truly encoded in single MI neurons.
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propagating waves mediate information transfer in the Motor Cortex
Nature Neuroscience, 2006Co-Authors: Doug Rubino, Kay A Robbins, Nicholas G. HatsopoulosAbstract:High-frequency oscillations in the beta range (10–45 Hz) are most active in Motor Cortex during Motor preparation and are postulated to reflect the steady postural state or global attentive state of the animal. By simultaneously recording multiple local field potential signals across the primary Motor and dorsal preMotor cortices of monkeys (Macaca mulatta) trained to perform an instructed-delay reaching task, we found that these oscillations propagated as waves across the surface of the Motor Cortex along dominant spatial axes characteristic of the local circuitry of the Motor Cortex. Moreover, we found that information about the visual target to be reached was encoded in terms of both latency and amplitude of evoked waves at a time when the field phase-locked with respect to the target onset. These findings suggest that high-frequency oscillations may subserve intra- and inter-cortical information transfer during movement preparation and execution.
P Storch - One of the best experts on this subject based on the ideXlab platform.
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Motor Cortex disinhibition in acute stroke
Clinical Neurophysiology, 2000Co-Authors: Joachim Liepert, P Storch, Andreas Fritsch, Cornelius WeillerAbstract:Abstract Objectives : To test whether a disinhibition occurs in the human Motor Cortex after stroke. Methods : Patients with a mild to moderate hemiparesis after an acute unilateral ischemic stroke were compared with age-matched healthy controls. We used paired transcranial magnetic stimuli (TMS) to investigate intracortical inhibition and facilitation. Single TMS were applied to obtain a cortical silent period. Results : Intracortical inhibition was significantly reduced in the affected hemisphere at interstimulus intervals of 2, 3 and 4 ms. The cortical silent period was significantly prolonged when compared to the unaffected hemisphere of the patients and to the control group. Motor Cortex disinhibition observed in stroke patients was associated either with minimal impairment at the onset of symptoms or with rapidly improving Motor functions. Conclusions : Motor Cortex disinhibition occurs in humans after stroke. We suggest that this disinhibition is indicative of compensatory mechanisms, which are involved in recovery-related reorganization.
