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Transcranial static magnetic field stimulation (tSMS) has inhibitory neuromodulatory effects on the human brain. Most of the studies on static magnetic fields have been performed in vitro. To further understand the biological mechanisms of tSMS, we investigated the effects of in vivo tSMS on motor behavior in normal awake rats. The skull of a male Wistar rat was exposed and a polyethylene tube was attached to the skull using dental cement at the center of the motor cortex (n = 7) or the other cortex (n = 6). By attaching a cylindrical NdFeB neodymium magnet into the tube, in vivo tSMS (REAL) was performed. For SHAM, we applied a similar size non-magnetic stainless-steel cylinder. All rats received twice each SHAM and REAL stimulation every two days using a crossover design, and motor function was measured during the stimulation. Activity level and asymmetry of forelimb use were not affected, but less accurate movements in the horizontal ladder test were found in REAL stimulation of the motor cortex. This study shows that in vivo tSMS has inhibitory neuromodulatory effects on motor behavior depending on the stimulated region on the rat cortex., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Low-intensity focused ultrasound induces neuronal activation via mechanisms that remain to be elucidated. We recorded local field potential fluctuations in the motor cortex in response to ultrasound stimulation of the somatosensory barrel cortex, comparing them to those recorded in response to optogenetic stimulation of interneurons and pyramidal neurons of the somatosensory cortex in the same animals. Comparison of the waveform produced by ultrasound stimulation to those produced by optogenetic stimulation revealed similarities between ultrasound-induced responses and optogenetically-induced responses to pyramidal cell stimulation, but not interneuron stimulation, which may indicate that ultrasound stimulation is mediated by excitation of cerebral cortical pyramidal neurons. Comparison of post mortem evoked responses to responses in living tissue confirmed the necessity for excitable tissue in the evoked response. Collectively, these experiments demonstrate an excitation-dependent response to low-frequency transdural ultrasound stimulation of cerebral cortical neuronal activity., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

In a typical flanker task, responses to a central target ("S" or "N") are modulated by whether the flankers are compatible ("SSSSS") or incompatible ("NNSNN"), with increased reaction times and decreased accuracy on incompatible trials. The role of the motor system in response interference under these conditions remains unclear, however. Here we show that transcranial magnetic stimulation (TMS) of the left primary motor cortex modulates the amount of flanker interference depending on the hand used for the response. Left motor TMS delivered at 200ms after the onset of the array increased interference from incompatible flankers ("SSNSS") when the target response was associated with the contralateral motor response (i.e. for "N" responses with the right hand), relative to when responses were to targets using the (left) hand ipsilateral to the site of TMS. Interestingly, under identical conditions, the degree of flanker interference was reduced when the TMS pulse was applied later in time. The analyses of the TMS-induced motor evoked potentials pointed to motor activity varying in the same conditions. We discuss the implications for understanding response interference and the role of the primary motor cortex in response selection.

The objective was to study whether repetitive transcranial magnetic stimulation (rTMS) of the motor cortex could induce modification of peripheral blood lactate values. Nineteen young healthy volunteers were included; during the study, all subjects were at rest, sitting on a comfortable armchair. The muscular activation was evaluated by continuous electromyographic record. TMS was performed by using a circular coil at the vertex. Resting motor threshold (rMT) was defined as the lowest TMS intensity able to induce motor responses of an amplitude >50 microV in the relaxed contralateral target muscle in approximately 50% of 20 consecutive stimuli. Venous blood lactate values were measured before, immediately after and 10 min after a single session of low frequencies (1Hz for 15 min) rTMS (LF rTMS) or high frequency (20 Hz for 15 min) rTMS (HF rTMS). As expected, LF rTMS induced a decrease of motor cortex excitability, whereas HF rTMS evoked an increase of motor cortex excitability. However, in the present investigation we observed that both conditions are associated to a significant increase of blood lactate. Since in our experimental conditions we can exclude a muscular production of lactate, the significant increment of peripheral blood lactate values, observed 10 min after the end of the rTMS session, is probably due to the crossing by brain-produced lactate of the blood-brain barrier.

The aim of this study was to investigate the influence of bromazepam on EEG and the motor learning process when healthy subjects were submitted to a typewriting task. We investigated bromazepam due to its abuse by various populations and its prevalent clinical use among older individuals which are more sensitive to the negative effects of long half-life benzodiazepines. A randomized double-blind design was used with subjects divided into three groups: placebo (n=13), bromazepam 3mg (n=13) and bromazepam 6 mg (n=13). EEG data comprising theta, alpha and beta bands was recorded before, during and after the motor task. Our results showed a lower relative power value in the theta band in the Br 6 mg group when compared with PL. We also observed a reduction in relative power in the beta band in the Br 3mg and Br 6 mg when compared with PL group. These findings suggest that Br can contribute to a reduced working memory load in areas related to attention processes. On the other hand, it produces a higher cortical activation in areas associated with sensory integration. Such areas are responsible for accomplishing the motor learning task. The results are an example of the usefulness of integrating electrophysiological data, sensorimotor activity and a pharmacological approach to aid in our understanding of cerebral changes produced by external agents.

Objective: To examine the changes in slow (8-10Hz) and fast (10-12Hz) alpha bands of EEG in three groups of subjects submitted to different amounts of functional electrostimulation (FES). Our hypothesis is that different amounts of electrostimulation may cause different patterns of activation in the sensorimotor cortex. In particular, we expect to see an increase in alpha power due to habituation effects. We examine the two bands comprised by alpha rhythm (i.e., slow and fast alpha), since these two sub-rhythms are related to distinct aspects: general energy demands and specific motor aspects, respectively., Methods: The sample was composed of 27 students, both sexes, aging between 25 and 40 years old. The subjects were randomly distributed in three groups: control (n=9), G24 (n=9) and G36 (n=9). A FES equipment (Neuro Compact-2462) was used to stimulate the right index finger extension. Simultaneously, the electroencephalographic signal was acquired. We investigated the absolute power in slow and fast alpha bands in the sensorimotor cortex., Results: The G36 indicated a significant increasing in absolute power values in lower and higher alpha components, respectively, when compared with the control group. Particularly, in the following regions: pre-motor cortex and primary motor cortex., Discussion: FES seems to promote cortical adaptations that are similar to those observed when someone learns a procedural task. FES application in the G36 was more effective in promoting such neural changes. The lower and higher components of alpha rhythms behave differently in their topographical distribution during FES application. These results suggest a somatotopic organization in primary motor cortex which can be represented by the fast alpha component.

The present study used short interval intracortical inhibition (SICI), intracortical facilitation (ICF), and short latency afferent inhibition (SAI) to evaluate motor cortex excitability in 16 diffuse axonal injury (DAI) patients with memory impairment and compared the data with those of 16 healthy controls. SAI was reduced in patients compared with controls (92+/-12 versus 39+/-11% of the test size; p<0.0001, unpaired t-test). DAI patients tended to have a high resting motor threshold (RMT) and less pronounced SICI and ICF than controls, but these differences were not significant. A single oral dose (3mg) of donepezil, an acetylcholinesterase inhibitor that is commonly used to treat Alzheimer's disease (AD), improved SAI in DAI patients with wide individual variations that ranged from an increase of 77-18% of test size. These findings suggest that measuring SAI may provide a means of probing the integrity of cholinergic networks in an injured human brain.

Functional neuroimaging techniques map neuronal activation indirectly via local concomitant cortical vascular/metabolic changes. In a complementary approach, DC-magnetoencephalography measures neuronal activation dynamics directly, notably in a time range of the slow vascular/metabolic response. Here, using this technique neuronal activation dynamics and patterns for simple and complex finger movements are characterized intraindividually: in 6/6 right-handed subjects contralateral prolonged (30 s each) complex self-paced sequential finger movements revealed stronger field amplitudes over the pericentral sensorimotor cortex than simple movements. A consistent lateralization for contralateral versus ipsilateral finger movements was not found (4/6). A subsequent sensory paradigm focused on somatosensory afferences during the motor tasks and the reliability of the measuring technique. In all six subjects stable sustained neuronal activation during electrical median nerve stimulation was recorded. These neuronal quasi-tonic activation characteristics provide a new non-invasive neurophysiological measure to interpret signals mapped by functional neuroimaging techniques.

In the present study, we analyzed how high-frequency repetitive transcranial magnetic stimulation (rTMS) of the primary motor hand area (M1-Hand) shapes anticipatory motor activity in frontal areas as indexed by the contingent negative variation (CNV). Eight right-handed volunteers received real or sham 5Hz rTMS at an intensity of 90% resting motor threshold (1,500 stimuli per session). Real but not sham rTMS to left M1-Hand induced a site-specific increase in amplitude of the late component of the CNV at the electrode C3 overlaying the site of stimulation. The increase in pre-movement activity in the stimulated cortex may reflect an increase in facilitatory drive from connected motor areas, enhanced responsiveness of the stimulated cortex to these inputs or both.

Single and paired-pulse transcranial magnetic stimulation (TMS) were applied to the motor cortex of 12 healthy volunteers, who were instructed to relax under eyes-open and eyes-closed conditions with room lights on and after 30 min of blindfolding. Compared to the eyes-open condition, significantly larger motor-evoked potentials and less intracortical inhibition were observed during blindfolding. Visual deafferentation changes resting human motor cortex excitability and might be a novel way to promote brain plasticity. These results raise the issue of how widespread the effects of temporary deafferentation may be and whether they are mediated by discrete or diffuse systems. These findings also illustrate an important potential confound in TMS studies of the motor cortex.

Acupuncture has been used extensively in facilitating motor recovery after stroke. Its mechanism of action remains uncertain. In this sham-controlled study, we demonstrate for the first time that acupuncture has a real and enduring effect on motor cortex functional changes, in terms of cortical excitability and output mapping using transcranial magnetic stimulation.

There is some evidence that repetitive transcranial magnetic stimulation (rTMS) can alleviate the experience of chronic pain. The mechanisms by which rTMS may induce pain relief, however, are unknown. The present study examined whether a session of rTMS would produce sensory threshold changes in healthy individuals. Detection and pain thresholds for cold sensations were compared following low frequency (1 Hz) (Experiment 1) and high frequency (20 Hz) (Experiment 2) repetitive TMS. While cold detection threshold was significantly lowered by both rTMS rates, only high frequency rTMS produced a significant change in cold pain threshold. In contrast, sham rTMS did not alter thresholds for cold stimuli. These findings provide evidence that sensory thresholds can be influenced by repetitive transcranial magnetic stimulation.

We investigated the effect of repetitive transcranial magnetic stimulation (rTMS) applied to the motor cortex, on the motor learning of sequential finger movements. Fifteen healthy subjects were trained to perform seven sequential finger movements of the left hand. Ten Hertz or sham rTMS with a resting motor threshold of 80% was applied to each subject during the task period. Stimulation with 10Hz rTMS produced a better learning performance in terms of target score and execution time than sham stimulation. We conclude that high-frequency rTMS may modulate the excitability of the motor cortex and facilitate the sequential motor learning process in normal subjects. These findings may provide a basis for the development of therapeutic applications of rTMS in patients with impaired motor skill.

Unilateral movements are enabled through a distributed network of motor cortical areas but the relative contribution from the parts of this network is largely unknown. Failure of this network potentially results in mirror activation of the primary motor cortex (M1) ipsilateral to the intended movement. Here we tested the role of the right dorsal premotor cortex (dPMC) in 11 healthy subjects by disrupting its activity with 20 Hz repetitive transcranial magnetic stimulation (rTMS) whilst the subjects exerted a unilateral contraction of the left first dorsal interosseous (FDI). We found that disruption of right dPMC enhanced mirror activation of the ipsilateral left M1, as probed by motor evoked potential (MEP) amplitude to the right FDI. This was not the case with sham rTMS, when rTMS was directed to the right M1, or with rTMS of the right dPMC but without contraction of the left FDI. Findings suggest that activity in the dPMC contributes to the suppression of mirror movements during intended unilateral movements.

Repetitive transcranial magnetic stimulation (TMS) for 1 s at 4 Hz and 150% of the individual motor threshold was applied to primary motor cortex and adjacent cortical regions where no motor response could be produced. The hemodynamic reaction was measured using an event-related functional magnetic resonance setup. While all volunteers showed a typical signal increase beneath the coil during motor cortex stimulation, no consistent signal changes were present during frontal or parietal stimulation apart from activation of auditory cortex. The results suggest that neuronal stimulation by TMS is followed by an inhibitive phase that compensates for the effect of an initial neuronal activation. It is further concluded that the signal increases during motor cortex fit a sensory feedback from the moving body parts., (Copyright 2002 Elsevier Science Ireland Ltd.)