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Li I Zhang - One of the best experts on this subject based on the ideXlab platform.
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Linear transformation of thalamocortical input by Intracortical excitation
Nature Neuroscience, 2013Co-Authors: Ya-tang Li, Leena A Ibrahim, Li I ZhangAbstract:By silencing Intracortical excitation in mouse primary visual cortex, Li and colleagues find that the tuning of layer 4 pyramidal cells is independent of cortico-cortical inputs. Instead, Intracortical excitation amplifies thalamocortical signals and expands the spatial receptive field of layer 4 neurons. Neurons in thalamorecipient layers of sensory cortices integrate thalamocortical and Intracortical inputs. Although we know that their functional properties can arise from the convergence of thalamic inputs, Intracortical circuits could also be involved in thalamocortical transformations of sensory information. We silenced Intracortical excitatory circuits with optogenetic activation of parvalbumin-positive inhibitory neurons in mouse primary visual cortex and compared visually evoked thalamocortical input with total excitation in the same layer 4 pyramidal neurons. We found that Intracortical excitatory circuits preserved the orientation and direction tuning of thalamocortical excitation, with a linear amplification of thalamocortical signals of about threefold. The spatial receptive field of thalamocortical input was slightly elongated and was expanded by Intracortical excitation in an approximately proportional manner. Thus, Intracortical excitatory circuits faithfully reinforce the representation of thalamocortical information and may influence the size of the receptive field by recruiting additional inputs.
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Intracortical multiplication of thalamocortical signals in mouse auditory cortex
Nature Neuroscience, 2013Co-Authors: Mu Zhou, Huizhong W. Tao, Li I ZhangAbstract:How the cortex processes and transforms sensory input coming from the thalamus is still a matter of debate. Here the authors optogenetically silence local cortical circuits to show that Intracortical excitation amplifies and prolongs thalamic inputs to the auditory cortex. Cortical processing of sensory information begins with the transformation of thalamically relayed signals. We optogenetically silenced Intracortical circuits to isolate thalamic inputs to layer 4 neurons and found that Intracortical excitation linearly amplified thalamocortical responses underlying frequency and direction selectivity, with spectral range and tuning preserved, and prolonged the response duration. This signal pre-amplification and prolongation enhanced the salience of thalamocortically relayed information and ensured its robust, faithful and more persistent representation.
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Linear transformation of thalamocortical input by Intracortical excitation.
Nature neuroscience, 2013Co-Authors: Leena A Ibrahim, Li I Zhang, Bao-hua Liu, Huizhong W. TaoAbstract:Neurons in thalamorecipient layers of sensory cortices integrate thalamocortical and Intracortical inputs. Although we know that their functional properties can arise from the convergence of thalamic inputs, Intracortical circuits could also be involved in thalamocortical transformations of sensory information. We silenced Intracortical excitatory circuits with optogenetic activation of parvalbumin-positive inhibitory neurons in mouse primary visual cortex and compared visually evoked thalamocortical input with total excitation in the same layer 4 pyramidal neurons. We found that Intracortical excitatory circuits preserved the orientation and direction tuning of thalamocortical excitation, with a linear amplification of thalamocortical signals of about threefold. The spatial receptive field of thalamocortical input was slightly elongated and was expanded by Intracortical excitation in an approximately proportional manner. Thus, Intracortical excitatory circuits faithfully reinforce the representation of thalamocortical information and may influence the size of the receptive field by recruiting additional inputs.
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Defining cortical frequency tuning with recurrent excitatory circuitry
Nature Neuroscience, 2007Co-Authors: Guangying K Wu, Robert Arbuckle, Li I ZhangAbstract:Neurons in the recipient layers of sensory cortices receive excitatory input from two major sources: the feedforward thalamocortical and recurrent Intracortical inputs. To address their respective functional roles, we developed a new method for silencing cortex by competitively activating GABA_A while blocking GABA_B receptors. In the rat primary auditory cortex, in vivo whole-cell recording from the same neuron before and after local cortical silencing revealed that thalamic input occupied the same area of frequency-intensity tonal receptive field as the total excitatory input, but showed a flattened tuning curve. In contrast, excitatory Intracortical input was sharply tuned with a tuning curve that closely matched that of suprathreshold responses. This can be attributed to a selective amplification of cortical cells' responses at preferred frequencies by Intracortical inputs from similarly tuned neurons. Thus, weakly tuned thalamocortical inputs determine the subthreshold responding range, whereas Intracortical inputs largely define the tuning. Such circuits may ensure a faithful conveyance of sensory information.
Robert Chen - One of the best experts on this subject based on the ideXlab platform.
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Increased Intracortical inhibition in hyperglycemic hemichorea-hemiballism.
Movement disorders : official journal of the Movement Disorder Society, 2014Co-Authors: Robert ChenAbstract:Hemichorea-hemiballism (HC-HB) in uncontrolled diabetes mellitus is an uncommon manifestation of hyperglycemia. The pathophysiology of hyperglycemic HC-HB is not well understood. A previous report showed increased Intracortical inhibition in the motor cortex in a patient with diabetes with HC-HB. The objective of this study is to investigate motor cortex excitability in patients with hyperglycemic HC-HB. We hypothesized that Intracortical inhibition measured with transcranial magnetic stimulation, which likely reflects the excitability of cortical γ-aminobutyric acid (GABA)ergic circuits, would be impaired in patients with hyperglycemic HC-HB. We studied 15 patients with mean age 71.5 years (range, 48-94 y) and 12 age-matched healthy subjects. The motor cortex contralateral to the hemichorea was tested. Transcranial magnetic stimulation measures included motor evoked potential, recruitment curve, GABAA mediated short interval Intracortical inhibition, Intracortical facilitation, and GABAB mediated silent period duration and long interval Intracortical inhibition. No significant difference was found in motor threshold, recruitment curve response, short interval Intracortical inhibition, or Intracortical facilitation in both rest and active conditions between patients with hyperglycemic HC-HB and normal subjects. However, long interval Intracortical inhibition was significantly increased during muscle activation but not at rest in patients with hyperglycemic HC-HB. The silent period duration is also increased in patients with hyperglycemic HC-HB. We concluded that long interval Intracortical inhibition and silent period are increased in the motor cortex contralateral to the hemichorea in hyperglycemic HC-HB, but only during muscle activation. Hemichorea-hemiballism may be associated with increased GABAB receptor-mediated inhibitory activity in the motor cortex. © 2014 International Parkinson and Movement Disorder Society
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heterosynaptic modulation of motor cortical plasticity in human
The Journal of Neuroscience, 2014Co-Authors: Carolyn Gunraj, Paramjit Kailey, Robin F H Cash, Robert ChenAbstract:Inductions of long-term potentiation (LTP) and depression (LTD) are modulated if they are preceded by a priming protocol, in a manner consistent with metaplasticity. Depotentiation refers to reversal of LTP by a subsequent protocol that has no effect by itself. Paired associative stimulation (PAS) at interstimulus interval of 25 ms (PAS25) and 10 ms (PAS10) produces spike timing-dependent LTP-like and LTD-like effects in human primary motor cortex. Continuous theta burst stimulation (cTBS) with 600 pulses produces an LTD-like effect, whereas cTBS with 150 pulses (cTBS150) has no effect by itself. We investigated whether cortical plasticity induced by PAS can be modulated by heterosynaptic inputs of cTBS150. PAS25 and PAS10 primed and followed by cTBS150 were compared withPAS25 and PAS10 alone. Motor evoked potential (MEP) amplitude, recruitment curve, and Intracortical circuits including short-interval Intracortical inhibition (SICI), long-interval Intracortical inhibition (LICI), Intracortical facilitation, and short-latency afferent inhibition were measured before and after the interventions. After PAS25 alone, MEP amplitude increased while Intracortical circuits did not change. A priming cTBS150 enhanced the effects of PAS25 with further increase in MEP amplitude and led to reduction in SICI and LICI. PAS25 followed by cTBS150 led to reduced MEP amplitude and increased LICI and SICI. Both priming and following cTBS150 reversed the LTD-like effect produced by PAS10 with little change in Intracortical circuits. We conclude that cortical plasticity induced by PAS and cTBS interacts in a heterosynaptic and bidirectional manner. The order of the interventions determines whether the underlying mechanisms are related to metaplasticity or depotentiation.
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selective effects of baclofen on use dependent modulation of gabab inhibition after tetraplegia
The Journal of Neuroscience, 2013Co-Authors: Melissa D Barry, Robert Chen, Karen L Bunday, Monica A. PerezAbstract:Baclofen is a GABAB receptor agonist commonly used to relief spasticity related to motor disorders. The effects of baclofen on voluntary motor output are limited and not yet understood. Using noninvasive transcranial magnetic and electrical stimulation techniques, we examined electrophysiological measures probably involving GABAB (long-interval Intracortical inhibition and the cortical silent period) and GABAA (short-interval Intracortical inhibition) receptors, which are inhibitory effects mediated by subcortical and cortical mechanisms. We demonstrate increased active long-interval Intracortical inhibition and prolonged cortical silent period during voluntary activity of an intrinsic finger muscle in humans with chronic incomplete cervical spinal cord injury (SCI) compared with age-matched controls, whereas resting long-interval Intracortical inhibition was unchanged. However, long-term (∼6 years) use of baclofen decreased active long-interval Intracortical inhibition to similar levels as controls but did not affect the duration of the cortical silent period. We found a correlation between signs of spasticity and long-interval Intracortical inhibition in patients with SCI. Short-interval Intracortical inhibition was decreased during voluntary contraction compared with rest but there was no effect of SCI or baclofen use. Together, these results demonstrate that baclofen selectively maintains use-dependent modulation of largely subcortical but not cortical GABAB neuronal pathways after human SCI. Thus, cortical GABAB circuits may be less sensitive to baclofen than spinal GABAB circuits. This may contribute to the limited effects of baclofen on voluntary motor output in subjects with motor disorders affected by spasticity.
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Intracortical Circuits and Their Interactions in Human Primary Motor Cortex
2012Co-Authors: Robert ChenAbstract:The human primary motor cortex (M1) works in association with other motor-related brain areas in the planning and execution of movements. Transcranial magnetic stimulation (TMS) is a widely used noninvasive brain stimulation technique and TMS studies have contributed significantly to our knowledge of motor cortical physiology. Single-pulse TMS activates the facilitatory interneurons in M1 and produces descending corticospinal volleys in the spinal cord, resulting in motor evoked potential in the target muscle. There are different inhibitory and facilitatory Intracortical circuits within the M1. The excitability of M1 is also modulated by interhemispheric inputs from the contralateral hemisphere and by inputs from premotor cortex, parietal cortex, cerebellum, and muscle afferents. The balance and interactions among the Intracortical circuits determine the final motor cortical output. Moreover, the Intracortical circuits are highly interconnected and the interactions among Intracortical circuits can be investigated by a triple-pulse TMS paradigm.
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Consensus paper on short-interval Intracortical inhibition and other transcranial magnetic stimulation Intracortical paradigms in movement disorders.
Brain stimulation, 2008Co-Authors: Alfredo Berardelli, Robert Chen, Antonio Suppa, Michael C. Ridding, Giovanni Abbruzzese, Michael Orth, Cathy M. Stinear, Carlo Trompetto, Philip D. ThompsonAbstract:In this article we reviewed the results obtained with the technique of paired-pulse transcranial magnetic stimulation (TMS) in normal subjects and in patients with movement disorders (Parkinson's disease, dystonia, chorea, Tourette's syndrome, myoclonus, essential tremor, and ataxia). Results on short-interval Intracortical inhibition (SICI), Intracortical facilitation (ICF) and long-interval Intracortical inhibition (LICI) are reported and discussed for each type of movement disorder.
John C. Rothwell - One of the best experts on this subject based on the ideXlab platform.
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Intracortical circuits sensorimotor integration and plasticity in human motor cortical projections to muscles of the lower face
The Journal of Physiology, 2013Co-Authors: G Pilurzi, John C. Rothwell, A Hasan, Tabish A Saifee, E Tolu, Franca DeriuAbstract:Previous studies of the cortical control of human facial muscles documented the distribution of corticobulbar projections and the presence of Intracortical inhibitory and facilitatory mechanisms. Yet surprisingly, given the importance and precision in control of facial expression, there have been no studies of the afferent modulation of corticobulbar excitability or of the plasticity of synaptic connections in the facial primary motor cortex (face M1). In 25 healthy volunteers, we used standard single- and paired-pulse transcranial magnetic stimulation (TMS) methods to probe motor-evoked potentials (MEPs), short-Intracortical inhibition, Intracortical facilitation, short-afferent and long-afferent inhibition and paired associative stimulation in relaxed and active depressor anguli oris muscles. Single-pulse TMS evoked bilateral MEPs at rest and during activity that were larger in contralateral muscles, confirming that corticobulbar projection to lower facial muscles is bilateral and asymmetric, with contralateral predominance. Both short-Intracortical inhibition and Intracortical facilitation were present bilaterally in resting and active conditions. Electrical stimulation of the facial nerve paired with a TMS pulse 5-200 ms later showed no short-afferent inhibition, but long-afferent inhibition was present. Paired associative stimulation tested with an electrical stimulation-TMS interval of 20 ms significantly facilitated MEPs for up to 30 min. The long-term potentiation, evoked for the first time in face M1, demonstrates that excitability of the facial motor cortex is prone to plastic changes after paired associative stimulation. Evaluation of Intracortical circuits in both relaxed and active lower facial muscles as well as of plasticity in the facial motor cortex may provide further physiological insight into pathologies affecting the facial motor system.
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state of the art pharmacologic effects on cortical excitability measures tested by transcranial magnetic stimulation
Brain Stimulation, 2008Co-Authors: Walter Paulus, Leonardo G. Cohen, John C. Rothwell, Joseph Classen, Charles H Large, Vincenzo Di Lazzaro, Michael A Nitsche, Alvaro Pascualleone, Felix Rosenow, Ulf ZiemannAbstract:The combination of brain stimulation techniques like transcranial magnetic stimulation (TMS) with CNS active drugs in humans now offers a unique opportunity to explore the physiologic effects of these substances in vivo in the human brain. Motor threshold, motor evoked potential size, motor evoked potential intensity curves, cortical silent period, short-interval Intracortical inhibition, Intracortical facilitation, short-interval Intracortical facilitation, long-interval Intracortical inhibition and short latency afferent inhibition represent the repertoire for investigating drug effects on motor cortical excitability by TMS. Here we present an updated overview on the pharmacophysiologic mechanisms with special emphasis on methodologic pitfalls and possible future developments or requirements.
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Intracortical inhibitory and excitatory circuits of the human masseteric motor cortex
Brain Stimulation, 2008Co-Authors: Enzo Ortu, Franca Deriu, Antonio Suppa, Elena Giaconi, Eusebio Tolu, John C. RothwellAbstract:Short interval Intracortical inhibition (SICI) and Intracortical facilitation (ICF) were evaluated in the masseter muscles of 12 subjects and the cortical silent period (SP) as well as long interval Intracortical inhibition (LICI) in 9 subjects.
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direct demonstration of the effect of lorazepam on the excitability of the human motor cortex
Clinical Neurophysiology, 2000Co-Authors: V Di Lazzaro, Antonio Oliviero, Mario Meglio, B Cioni, Gianpiero Tamburrini, P Tonali, John C. RothwellAbstract:Abstract Objectives : The present study explored the effects of lorazepam, a benzodiazepine with agonist action at the GABA A receptor, on human motor cortex excitability as tested using transcranial magnetic stimulation. Methods : We recorded directly the descending volley evoked by single and paired transcranial magnetic stimulation from the spinal cord of a conscious subject with a cervical epidural electrode before and after a single oral dose of lorazepam. We evaluated the effects of lorazepam on the descending volleys evoked by a single magnetic stimulation and paired cortical stimulation using the Intracortical inhibition paradigm (subthreshold conditioning stimulus) and the short latency Intracortical facilitation paradigm (suprathreshold conditioning stimulus). Results : Using a single magnetic stimulus lorazepam decreased the amplitude of the later I waves in the descending volley; this was accompanied by a decrease in the amplitude of the evoked EMG response. Using the Intracortical inhibition paradigm lorazepam increased the amount of corticocortical inhibition, particularly at 4 and 5 ms interstimulus intervals. There was no effect on the amount of facilitation observed in the short latency Intracortical facilitation paradigm. Conclusions : The present findings provide direct evidence that lorazepam increases the excitability of inhibitory circuits in the human motor cortex.
Alfredo Berardelli - One of the best experts on this subject based on the ideXlab platform.
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Consensus paper on short-interval Intracortical inhibition and other transcranial magnetic stimulation Intracortical paradigms in movement disorders.
Brain stimulation, 2008Co-Authors: Alfredo Berardelli, Robert Chen, Antonio Suppa, Michael C. Ridding, Giovanni Abbruzzese, Michael Orth, Cathy M. Stinear, Carlo Trompetto, Philip D. ThompsonAbstract:In this article we reviewed the results obtained with the technique of paired-pulse transcranial magnetic stimulation (TMS) in normal subjects and in patients with movement disorders (Parkinson's disease, dystonia, chorea, Tourette's syndrome, myoclonus, essential tremor, and ataxia). Results on short-interval Intracortical inhibition (SICI), Intracortical facilitation (ICF) and long-interval Intracortical inhibition (LICI) are reported and discussed for each type of movement disorder.
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Effects of attention on inhibitory and facilitatory phenomena elicited by paired-pulse transcranial magnetic stimulation in healthy subjects
Experimental Brain Research, 2008Co-Authors: Antonella Conte, Daniele Belvisi, Ennio Iezzi, Francesco Mari, Maurizio Inghilleri, Alfredo BerardelliAbstract:We investigated whether human attentional processes influence the activity of Intracortical inhibitory and excitatory circuits—short-interval Intracortical inhibition (SICI), long-interval Intracortical inhibition (LICI), and the Intracortical facilitation (ICF)—elicited by paired-pulse transcranial magnetic stimulation (TMS) in healthy subjects. In eight healthy subjects we tested SICI, LICI and ICF under different attention-demanding conditions: “relaxed”, “target hand” and “non-target hand”. To compare the effects of attentional levels on SICI, LICI and ICF with those produced on the MEPs elicited by repetitive TMS (rTMS), in the same subjects we also delivered supra-threshold 5-Hz rTMS under the same three experimental conditions. To disclose whether attentional processes act selectively on circuits engaged by TMS delivered at 5 Hz frequency and at an interstimulus interval (ISI) of 200 ms, we also investigated the effects of different attention levels on paired-pulse TMS delivered at the 200 ms ISI and on the MEP size during 1-Hz rTMS. Attentional levels had no influence on SICI, ICF and LICI activated by paired-pulse TMS, but increased the MEP facilitation elicited by 5-Hz rTMS. Varying the attention level left the findings from 1-Hz rTMS unchanged. The finding that attention leaves the activity of Intracortical inhibitory and excitatory circuits elicited by paired-pulse TMS unchanged but influences the MEP facilitation elicited by 5-Hz rTMS suggests that attention operates only when the stimulation entrains neural circuits made up of a large number of cortical cells with plasticity properties.
Hartwig R Siebne - One of the best experts on this subject based on the ideXlab platform.
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age related decrease in paired pulse Intracortical inhibition in the human primary motor cortex
Neuroscience Letters, 2001Co-Authors: Alexande Peinema, Christia Lehne, Astia Conrad, Hartwig R SiebneAbstract:Abstract Using biphasic magnetic stimuli, paired-pulse transcranial magnetic stimulation (TMS) at short interstimulus intervals (ISIs) was employed to investigate age-related changes in the balance between Intracortical inhibition and facilitation. In 26 right-handed healthy individuals, motor evoked potentials were recorded from the relaxed right first dorsal interosseus muscle after paired-pulse TMS of the left primary motor hand area. The magnitude of Intracortical paired-pulse inhibition at ISIs of 1–5 ms was markedly reduced in elderly individuals, whereas no age effect was observed for Intracortical paired-pulse facilitation at ISIs of 11–15 ms. This finding demonstrates that normal aging is associated with a relative decrease in the excitability of Intracortical inhibitory circuits. In conclusion, paired-pulse TMS provides a non-invasive means of studying age-related functional changes in the motor cortex.