Decrease In Intracortical Inhibition Research Articles

Relationship between the interlimb transfer of a visuomotor learning task and interhemispheric inhibition in healthy humans.

The "interlimb transfer" phenomenon consists of improved performance of the trained and untrained contralateral limbs after unilateral motor practice. We here assessed whether a visuomotor learning task can be transferred from one hemisphere to the other, whether this occurs symmetrically, and the cortical neurophysiological correlates of this phenomenon, focusing on interhemispheric connectivity measures. We enrolled 33 healthy subjects (age range: 24-73years). Participants underwent two randomized sessions, which investigated the transfer from the dominant to the nondominant hand and vice versa. Measures of cortical and intracortical excitability and interhemispheric inhibition were assessed through transcranial magnetic stimulation before and after a visuomotor task. The execution of the visuomotor task led to an improvement in motor performance with the dominant and nondominant hands and induced a decrease in intracortical inhibition in the trained hemisphere. Participants were also able to transfer the visuomotor learned skill. The interlimb transfer, however, only occurred from the dominant to the nondominant hand and positively correlated with individual learning-related changes in interhemispheric inhibition. We here demonstrated that the "interlimb transfer" of a visuomotor task occurs asymmetrically and relates to the modulation of specific inhibitory interhemispheric connections. The study results have pathophysiological, clinical, and neuro-rehabilitative implications.

Graded motor imagery modifies movement pain, cortical excitability and sensorimotor function in complex regional pain syndrome.

Patients with complex regional pain syndrome suffer from chronic neuropathic pain and also show a decrease in sensorimotor performance associated with characteristic central and peripheral neural system parameters. In the brain imaging domain, these comprise altered functional sensorimotor representation for the affected hand side. With regard to neurophysiology, a decrease in intracortical inhibition for the sensorimotor cortex contralateral to the affected hand has been repetitively verified, which might be related to increased primary somatosensory cortex functional activation for the affected limb. Rare longitudinal intervention studies in randomized controlled trials have demonstrated that a decrease in primary somatosensory cortex functional MRI activation coincided with pain relief and recovery in sensorimotor performance. By applying a randomized wait-list control crossover study design, we tested possible associations of clinical, imaging and neurophysiology parameters in 21 patients with complex regional pain syndrome in the chronic stage (>6 months). In more detail, we applied graded motor imagery over 6 weeks to relieve movement pain of the affected upper limb. First, baseline parameters were tested between the affected and the non-affected upper limb side and age-matched healthy controls. Second, longitudinal changes in clinical and testing parameters were associated with neurophysiological and imaging parameters. During baseline short intracortical inhibition, as assessed with transcranial magnetic stimulation, was decreased only for hand muscles of the affected hand side. During movement of the affected limb, primary somatosensory cortex functional MRI activation was increased. Hand representation area size for somatosensory stimulation in functional MRI was smaller on the affected side with longer disease duration. Graded motor imagery intervention but not waiting, resulted in a decrease of movement pain. An increase of somatosensory hand representation size over graded motor imagery intervention was related to movement pain relief. Over graded motor imagery intervention, pathological parameters like the increased primary somatosensory cortex activation during fist movement or decreased short intracortical inhibition were modified in the same way as movement pain and hand performance improved. No such changes were observed during the waiting period. Overall, we demonstrated characteristic changes in clinical, behaviour and neuropathology parameters applying graded motor imagery in patients with upper limb complex regional pain syndrome, which casts light on the effects of graded motor imagery intervention on biomarkers for chronic neuropathic pain.

Differential effects of motor skill acquisition on the primary motor and sensory cortices in healthy humans

We explored the large variability in motor skill acquisition-related effects on the primary and sensory cortices. Namely, we tested whether this variability depends on interindividual variance or the type of motor task investigated. We compared different motor-learning tasks, i.e. model-free vs. model-based learning tasks, and their possible differential effects on the primary motor and sensory cortices by using transcranial magnetic stimulation techniques. The model-free learning task induced an increase in corticospinal excitability and a reduction in the amplitude of somatosensory-evoked potentials. Conversely, the model-based learning tasks induced a decrease in intracortical inhibition. No correlations were found between neurophysiological changes and motor performance, indicating that this differential modulation may be secondary to the motor skill acquisition. The study results suggest differential motor skill acquisition-related effects on cortical parameters, possibly due to the engagement of specific neurophysiological substrates. A large variability in learning-related neurophysiological changes in the primary motor and sensory cortices has been observed. It is unclear whether these differential effects are due to the different tasks investigated or to interindividual variance. Only a few studies have assessed different motor-learning tasks and their effects on neurophysiological features within the same group of participants, and several issues are unclear. Here, we compared the effects of different tasks within each individual. We investigated the effects on motor and sensory cortex parameters after a model-free learning task, i.e. a ballistic motor task, compared with model-based learning tasks, i.e. visuomotor-learning tasks. Motor- and sensory-evoked potentials, intracortical excitability as assessed by short-interval intracortical inhibition, and sensorimotor interaction, i.e. short-latency afferent inhibition, were recorded from 15 healthy subjects before and after the tasks. The ballistic motor task induced an increase in corticospinal excitability but did not change motor cortex intracortical inhibition or sensorimotor integration. In addition, it decreased the amplitude of cortical components of the somatosensory-evoked potentials. The visuomotor-learning tasks induced a reduction in motor cortex intracortical inhibition but did not modulate corticospinal and sensory cortex excitability or sensorimotor integration. This differential modulation is likely to be secondary to the motor skill acquisition, since no correlation was observed between neurophysiological changes and motor performance. Our results demonstrate differential motor skill acquisition-related effects on cortical parameters, possibly reflecting the engagement of specific neurophysiological substrates, and contribute in-depth knowledge of the mechanisms involved in different types of motor skill acquisition in humans.

Intracortical motor networks are affected in both the contralateral and ipsilateral hemisphere during single limb cold water immersion.

What is the central question of this study? How does single limb cold water immersion affect corticomotor function and intracortical circuitry in the motor cortex of each cerebral hemisphere? What is the main finding and its importance? Immersion of a single limb in very cold water caused an increase in corticomotor excitability and intracortical facilitation, and a decrease in intracortical inhibition, in the motor cortex of both hemispheres. These findings provide evidence that intense sensory stimuli induce widespread changes in motor circuitry in the contralateral, as well as the ipsilateral, hemisphere. Although responses to noxious stimuli have been extensively studied for the contralateral hemisphere, little is known about how the ipsilateral hemisphere may be affected. Therefore, this study examined how exposing a single limb to noxious cold stimuli affects motor output arising from both the contralateral and ipsilateral hemisphere. A total of 17 healthy adults participated in three experiments. Single- and paired-pulse TMS protocols were used to identify how immersing a single upper limb in cold water (4.0±0.5°C) affects inhibitory and facilitatory circuits in the primary motor cortex (M1) of the contralateral (experiment 1) and ipsilateral (experiment 2) hemisphere. The third experiment used a reaction time task to assess the functional consequences of acute adaptations in the ipsilateral M1. The target muscle in all experiments was the extensor carpi radialis brevis (ECRB). Immersion of a single limb in cold water increased self-perception of pain and temperature, and increased EMG amplitude of the immersed limb. During immersion, motor evoked potentials and intracortical facilitation increased, whereas short interval intracortical inhibition decreased, for both the ipsilateral M1 and contralateral M1. Activity in the ipsilateral hemisphere to the limb immersed in cold water also slowed reaction time for the non-immersed limb. Our findings suggest that altered motor responses from single limb cold water immersion are not restricted to a single hemisphere. Instead, widespread activation of somatosensory systems influences inhibitory and facilitatory circuits in the primary motor cortex of each hemisphere.

Intermittent single-joint fatiguing exercise reduces TMS-EEG measures of cortical inhibition.

Fatiguing intermittent single-joint exercise causes an increase in corticospinal excitability and a decrease in intracortical inhibition when measured with peripherally recorded motor evoked potentials (MEPs) after transcranial magnetic stimulation (TMS). Combined TMS and electroencephalography (TMS-EEG) allows for more direct recording of cortical responses through the TMS-evoked potential (TEP). The aim of this study was to investigate the changes in the excitatory and inhibitory components of the TEP during fatiguing single-joint exercise. Twenty-three young (22 ± 2 yr) healthy subjects performed intermittent 30-s maximum voluntary contractions of the right first dorsal interosseous muscle, followed by a 30-s relaxation period repeated for a total of 15 min. Six single-pulse TMSs and one peripheral nerve stimulation (PNS) to evoke maximal M wave (Mmax) were applied during each relaxation period. A total of 90 TMS pulses and 5 PNSs were applied before and after fatiguing exercise to record MEP and TEP. The amplitude of the MEP (normalized to Mmax) increased during fatiguing exercise ( P < 0.001). There were no changes in local and global P30, N45, and P180 of TEPs during the development of intermittent single-joint exercise-induced fatigue. Global analysis, however, revealed a decrease in N100 peak of the TEP during fatiguing exercise compared with before fatiguing exercise ( P = 0.02). The decrease in N100 suggests a fatigue-related decrease in global intracortical GABAB-mediated inhibition. The increase in corticospinal excitability typically observed during single-joint fatiguing exercise may be mediated by a global decrease in intracortical inhibition. NEW & NOTEWORTHY Fatiguing intermittent single-joint exercise causes an increase in corticospinal excitability and a decrease in intracortical inhibition when measured with transcranial magnetic stimulation (TMS)-evoked potentials from the muscle. The present study provides new and direct cortical evidence, using TMS-EEG to demonstrate that during single-joint fatiguing exercise there is a global decrease in intracortical GABAB-mediated inhibition.

The effects of transcranial alternating current stimulation (tACS) at individual alpha peak frequency (iAPF) on motor cortex excitability in young and elderly adults

Transcranial alternating current stimulation (tACS) can modulate brain oscillations, cortical excitability and behaviour. In aging, the decrease in EEG alpha activity (8–12 Hz) in the parieto-occipital and mu rhythm in the motor cortex are correlated with the decline in cognitive and motor functions, respectively. Increasing alpha activity using tACS might therefore improve cognitive and motor function in the elderly. The present study explored the influence of tACS on cortical excitability in young and old healthy adults. We applied tACS at individual alpha peak frequency for 10 min (1.5 mA) to the left motor cortex. Transcranial magnetic stimulation was used to assess the changes in cortical excitability as measured by motor-evoked potentials at rest, before and after stimulation. TACS increased cortical excitability in both groups. However, our results also suggest that the mechanism behind the effects was different, as we observed an increase and decrease in intracortical inhibition in the old group and young group, respectively. Our results indicate that both groups profited similarly from the stimulation. There was no indication that tACS was more effective in conditions of low alpha power, that is, in the elderly.

Cortical involvement in myopathies: Insights from transcranial magnetic stimulation

ObjectiveThere is increasing evidence that an involvement of central nervous system (CNS) can occur in several myopathies. Transcranial magnetic stimulation (TMS) may represent a valuable tool for investigating important neurophysiological and pathophysiological aspects of cortical involvement in neuromuscular disorders. In this review paper we aimed to perform a systematic search of the studies employing TMS techniques in subjects suffering from myopathies. MethodsA literature search was conducted using PubMed and Embase. We identified and reviewed 9 articles matching the inclusion criteria. One hundred twenty patients were included in these studies, which have applied TMS in patients with muscle disorders. ResultsTo date, a few studies using TMS have been performed in myopathic patients and detected subclinical abnormalities in cortical reactivity and plasticity. The most consistent finding was a decrease in intracortical inhibition, which likely represents a non-specific compensatory mechanism of the CNS in an attempt to overcome the muscle deficit through an increase of the motor cortex output to deficient muscles. ConclusionsApplication of TMS to characterize the pathophysiology of the CNS in these subjects appears to be safe and may lead to the development of valuable biomarkers. Well-defined motor cortical excitability patterns can be identified in the different muscle diseases, even if preliminary findings should be confirmed in future studies in larger cohorts of patients. SignificanceTMS studies may shed new light on the physiological and pathophysiological mechanisms underlying the cortical involvement in muscle disorders.

Movement observation-induced modulation of pain perception and motor cortex excitability

ObjectiveThe observation of movements increases primary motor cortex (M1) excitability. This exploratory study examined the effects of movement observation on pressure pain threshold (PPT) and transcranial magnetic stimulation (TMS)-indexed corticospinal excitability bilaterally. MethodsThirty healthy right-handed subjects were randomized to a left hand-movement observation task or a control task. Statistical analyses were performed using ANOVA models and t-tests. Results were not corrected for multiple comparisons. Quantitative sensory assessments were measured in both hands, while M1 excitability has only been tested for the right (non-dominant) M1 corresponding to the observed left hand movements. ResultsAnalysis of pain and cortical silent period (CSP) outcomes demonstrated a significant interaction between task (hand-movement group) versus control group and time (pre-/postintervention). PPT increased in the left hand (moving hand in the task) and declined significantly in the contralateral hand (still hand) in the movement-observation-task-group, whereas PTT in the control group remained unchanged. CSP was significantly shorter in the movement-observation group indicating decreased intracortical inhibition (results uncorrected for multiple comparisons). ConclusionsThe observation of hand-movements led to a side-specific reduction in pain perception and a decrease in intracortical inhibition. SignificanceThese exploratory findings support the notion that M1 is a robust modulator of pain-related neural networks. This effect might be mediated through modulation of the GABAergic system and appears to differ from what is observed in chronic pain.

Aerobic exercise modulates intracortical inhibition and facilitation in a nonexercised upper limb muscle.

BackgroundDespite growing interest in the relationship between exercise and short-term neural plasticity, the effects of exercise on motor cortical (M1) excitability are not well studied. Acute, lower-limb aerobic exercise may potentially modulate M1 excitability in working muscles, but the effects on muscles not involved in the exercise are unknown. Here we examined the excitability changes in an upper limb muscle representation following a single session of lower body aerobic exercise. Investigating the response to exercise in a non-exercised muscle may help to determine the clinical usefulness of lower-body exercise interventions for upper limb neurorehabilitation.MethodsIn this study, transcranial magnetic stimulation was used to assess input–output curves, short-interval intracortical inhibition (SICI), long-interval intracortical inhibition (LICI) and intracortical facilitation (ICF) in the extensor carpi radialis muscle in twelve healthy individuals following a single session of moderate stationary biking. Additionally, we examined whether the presence of a common polymorphism of the brain-derived neurotrophic factor (BDNF) gene would affect the response of these measures to exercise.ResultsWe observed significant increases in ICF and decreases in SICI following exercise. No changes in LICI were detected, and no differences were observed in input–output curves following exercise, or between BDNF groups.ConclusionsThe current results demonstrate that the modulation of intracortical excitability following aerobic exercise is not limited to those muscles involved in the exercise, and that while exercise does not directly modulate the excitability of motor neurons, it may facilitate the induction of experience-dependent plasticity via a decrease in intracortical inhibition and increase in intracortical facilitation. These findings indicate that exercise may create favourable conditions for adaptive plasticity in M1 and may be an effective adjunct to traditional training or rehabilitation methods.

Multiple EMG Activity and Intracortical Inhibition and Facilitation During a Fine Finger Movement Under Pressure

ABSTRACT The 1st purpose of this study was to examine multiple electromyography (EMG) during voluntary hand movements. A secondary purpose was to investigate possible effects of pressure on intracortical inhibition (ICI) and intracortical facilitation (ICF) functions of the motor cortex, using paired-pulse transcranial magnetic stimulation. Twelve participants traced a 15-cm diameter target circle using a small laser pointer attached to the right index finger. After 5 acquisition trials, they performed 3 nonpressure trials followed by 3 pressure trials. The results showed that pressure had effects not only on agonist EMG activity but also on multiple muscles, such as synergist. In addition, a decrease in ICI and an increase in ICF were both observed under pressure for muscles other than the agonist.

Motor cortex excitability changes during imagery of simple reaction time

Imagining motor actions is enough to enhance cortical motor excitability. However, the fact that execution of the motor task has to be inhibited should have a correlate on the extent of cortical excitability enhancement. Therefore, we examined the possible differences between real and motor imagery of simple reaction time tasks (SRT) in the facilitation of the motor-evoked potential (MEP) to transcranial magnetic stimulation (TMS) and in the reduction of short-interval intracortical inhibition (SICI) taking place before the movement onset. Thirteen healthy volunteers were requested to perform visual real or imaginary SRT tasks (rSRT and iSRT) with their dominant hand. For rSRT, subjects had to perform a rapid isometric squeeze as soon as possible after the imperative signal. For iSRT they had to imagine the same movement without actually doing it. Electromyographic (EMG) signals were recorded from the first dorsal interosseus (FDI) muscle. The mean EMG onset was calculated for each subject in rSRT trials. Single-and paired-pulse TMS (at an interstimulus interval of 2.5 ms) were applied at rest and at time intervals of -25, -50, -75, -100 and -125 ms before the expected real (rSRT) mean EMG onset. In rSRT there was a significant increase of MEP to single-pulseTMS at the intervals of -50 and -25 ms, and in iSRT at -50 ms in comparison to the rest condition. % SICI changes were significantly reduced at the intervals of -75, -50 and -25 ms, before EMG the onset in rSRT and at -50 and -25 in iSRT (P < 0.05) in comparison to % SICI changes at rest. The differences between MEPs to spTMS and MEP to ppTMS were significantly larger at rest, -125 and -100 ms intervals in rSRT, and at all intervals in iSRT. Imagining to move causes an increase in corticospinal excitability and a decrease in intracortical inhibition that follow a temporal profile similar to those observed with real movements. However, complete removal of SICI happened only in rSRT at the shortest intervals before the EMG onset. Such action may delineate new tool in motor rehabilitation of patients who have limitation to move.

Possible mechanisms underlying tilt aftereffect in the primary visual cortex: A critical analysis with the aid of simple computational models

A mathematical model of orientation selectivity in a single hypercolumn of the primary visual cortex developed in a previous work [Ursino, M., & La Cara, G.-E. (2004). Comparison of different models of orientation selectivity based on distinct intracortical inhibition rules. Vision Research, 44, 1641–1658] was used to analyze the possible mechanisms underlying tilt aftereffect (TAE). Two alternative models are considered, based on a different arrangement of intracortical inhibition (an anti-phase model in which inhibition is in phase opposition with excitation, and an in-phase model in which inhibition has the same phase arrangement as excitation but wider orientation selectivity). Different combinations of parameter changes were tested to explain TAE: a threshold increase in excitatory and inhibitory cortical neurons (fatigue), a decrease in intracortical excitation, an increase or a decrease in intracortical inhibition, a decrease in thalamo-cortical synapses. All synaptic changes were calculated on the basis of Hebbian (or anti-Hebbian) rules. Results demonstrated that the in-phase model accounts for several literature results with different combinations of parameter changes requiring: (i) a depressive mechanism to neurons with preferred orientation close to the adaptation orientation (fatigue of excitatory cortical neurons, and/or depression of thalamo-cortical synapses directed to excitatory neurons, and/or depression of intracortical excitatory synapses); (ii) a facilitatory mechanism to neurons with preferred orientation far from the adaptation orientation (fatigue of inhibitory cortical neurons, and/or depression of thalamo-cortical synapses directed to inhibitory neurons, and/or depression of intracortical inhibitory synapses). By contrast, the anti-phase model appeared less suitable to explain experimental data.

Hyperexcitable cortical responses in progressive myoclonic epilepsy: a TMS study.

Transcranial magnetic stimulation (TMS) has allowed investigators to study intracortical inhibition and facilitation and sensorimotor integration in motor disorders and epilepsy. The authors used TMS to elucidate the pathophysiology of reflex myoclonus with giant somatosensory evoked potentials (SEP). The authors studied four patients with progressive myoclonic epilepsy. All patients had giant SEP elicited by mixed and digital nerve stimulation. They studied the response to paired-pulse TMS at interstimulus intervals (ISI) ranging from 1 to 15 ms and the conditioning effect of digital electrical stimulation at ISI ranging from 10 to 100 ms on the motor evoked potential amplitude to TMS. Digital stimulation markedly facilitated conditioned motor evoked potentials at ISI ranging from 25 to 40 ms in all patients. This pattern was significantly different from the inhibition observed in controls (n = 12) at the same ISI. In the patients, paired-pulse TMS showed a decrease in intracortical inhibition in the motor cortex in comparison with controls. These findings suggest cortical and subcortical components of abnormal sensorimotor integration in addition to hyperexcitability of the sensory and motor cortex in our myoclonic patients.

Changes in human motor cortex excitability induced by dopaminergic and anti-dopaminergic drugs

Transcranial magnetic stimulation was used to probe the acute effect of a single oral dose of various dopaminergic (levodopa, selegiline, bromocriptine) and antidopaminergic drugs (sulpiride, haloperidol) on motor cortex excitability in healthy volunteers. Motor threshold, intracortical inhibition and intracortical facilitation were tested in the abductor digiti minimi muscle. The latter two parameters were studied in a conditioning-test paired stimulus paradigm. The principal findings were an increase in intracortical inhibition by bromocriptine, and, conversely, a decrease in intracortical inhibition and an increase in intracortical facilitation by haloperidol. Effects peaked at delays consistent with the pharmacokinetics of the two drugs and were fully reversible. In conclusion, dopamine receptor agonists and antagonists can be considered inverse modulators of motor cortex excitability: the former enhance inhibition while the latter reduce it. The relation of the present findings to current models of motor excitability abnormalities in movement disorders will be discussed.