Pupillary reactions during transcranial magnetic stimulation

Pupillary reactions have been studied in healthy volunteers before, during, and after transcranial magnetic stimulation (TMS) of the primary visual cortex. During TMS in the projection of the primary visual cortex, a significant increase in pupil size was observed. Three minutes after the end of the TMS, a significant decrease in pupil size was recorded. These data point to a role of the primary visual cortex in the mechanisms of correcting pupillary reactions in humans.     

跨颅电刺激对大鼠抑郁症的治疗作用

目的：探讨跨颅电刺激对大鼠抑郁症的治疗作用。方法：跨颅电刺激抑郁症大鼠左侧前额叶皮层,敞箱实验测定大鼠行为学变化,荧光法测定单胺类递质含量的变化。结果：跨颅直流电和低频脉冲电刺激后,大鼠敞箱实验中垂直和水平运动得分均较模型组显著升高（P〈0.05）;且大鼠左侧前额叶皮层和海马5-HT、NE含量较模型组显著升高（P〈0.05）,而前额叶皮层DA含量无显著变化（P〉0.05）。结论：直流电和低频脉冲电跨颅刺激左侧前额叶皮层,对抑郁症均有显著治疗作用。     

Healthy person's cerebral reactions to the rhythmic transcranial magnetic stimulation of different intensity

At 8 healthy examinees-volunteers of 22-25 years the functional effects of super-threshold (above 1.2 T) and subthreshold (70-80% of a motor threshold) rTMS of premotor cortexes medial departments were compared. Functional brain activity changes were estimated (before and 1 hour after stimulation) by comparing data including neuropsychological testing, visual and spectral-coherent EEG-analysis, and also haemodynamic parameters. The number of the work's problem included selection of activating orientated stimulation's frequency, and also specification objective EEG--criteria of efficiency rTMS. It is established the effect of EEG-analysis during different frequency photostimulation for a choice of activating rTMS. The received results reveal EEG-coherence as one of the most informative characteristics of cerebral neuro-dynamics under rTMS-influence. Dependence of stimulation's functional effects (activated or brake character) from initial level of the intercentral coherent communications is noted. It is revealed that rTMS of the healthy examinees causes certain changes of functional activity of a brain, distinct from placebo-effects. rTMS-effect dependent on intensity (super--or sub-threshold), and also from features of an initial intercentral rations. More expressed functional changes are observed in the left hemisphere. It is shown big by reactance of the left hemisphere on this influence. In formation of brain responses on rTMS the active role of the vascular factor is shown.     

Effect of transcranial electrical stimulation on sleep in rats

Transcranial electrical stimulation with high frequency intermittent current (Limoge's current) was delivered to normal rats and to PCPA-treated rats with impaired sleep. Electrocorticogram was continuously recorded for quantifying the stage of the sleep-waking cycle. The current did not affect the sleep pattern of normal rats whereas the number of paradoxical sleep episodes increased in insomniac animals. The increased duration of paradoxical sleep in PCPA-treated rats favored the recovery of sleep in this group. The stimulation increased the brain serotonin turnover, which could possibly contribute to its hypnogenic action.     

Effects of exhaustive incremental treadmill exercise on diaphragm and quadriceps motor potentials evoked by transcranial magnetic stimulation.

It is unknown whether changes in corticomotor excitability follow exercise in healthy humans. We hypothesized that a fall in the diaphragm and quadriceps motor-evoked potential (MEP) amplitude elicited by transcranial magnetic stimulation of the motor cortex would occur after an incremental exercise task. In 11 healthy subjects, we measured transdiaphragmatic pressure and isometric quadriceps tension in response to supramaximal peripheral magnetic nerve stimulation. MEPs were recorded from these muscles in response to transcranial magnetic stimulation. After baseline measurements, subjects performed a period of submaximal exercise (gentle walking). Measurements were repeated 5 and 20 min after this. The subjects then exercised on a treadmill with an incremental protocol to exhaustion. Transcranial magnetic stimulation was performed at baseline and at 5, 20, 40, and 60 min after exhaustive exercise, and force measurements were obtained at baseline, 20 min, and 60 min. Mean exercise duration was 18 +/- 4 min, and mean maximum heart rate was 172 +/- 10 beats/min. Twitch transdiaphragmatic pressure and twitch isometric quadriceps tension were not different from baseline after exercise, but a significant decrease was observed in diaphragm MEP amplitude 5 and 20 min after exercise (60 +/- 38 and 45 +/- 24%, respectively, of baseline, P = 0.0001). At the same times, the mean quadriceps MEPs were 59 +/- 39 and 74 +/- 32% of baseline (P < 0.0001 and P < 0.01, respectively). Studies using paired stimuli confirmed a likely intracortical mechanism for this depression. Our data confirm significant depression of both diaphragm and quadriceps MEPs after incremental treadmill exercise.     

Repetitive transcranial magnetic stimulation and treatment of negative symptoms of schizophrenia

One of the fundamental prerequisites of the successful schizophrenia treatment is represented by an adequately significant impact on the negative symptoms of schizophrenia. Since the present pharmacotherapy has probably reached its limit in this area, there is a logical effort to utilize other, non-pharmacological methods. One of the most promising supplements that has been for a long time verified in the clinical practice is rTMS. Most of the studies have arrived at the conclusion that rTMS is an efficient method in the treatment of negative symptoms of schizophrenia. A valuable contribution to the assessment of the rTMS application in the treatment of negative symptoms is represented by meta-analyses. The meta-analyses indicate that the effect is mild to moderate (d=0.43 to 0.68). To sum it up, there will be higher probability of the rTMS effect on negative symptoms if 10?Hz stimulating frequency and a longer stimulation period in the extent at least three, ideally four to six weeks is used.     

The effect of repetitive transcranial magnetic stimulation on gamma oscillatory activity in schizophrenia

Background

Gamma (γ) oscillations (30–50 Hz) have been shown to be excessive in patients with schizophrenia (SCZ) during working memory (WM). WM is a cognitive process that involves the online maintenance and manipulation of information that is mediated largely by the dorsolateral prefrontal cortex (DLPFC). Repetitive transcranial magnetic stimulation (rTMS) represents a non-invasive method to stimulate the cortex that has been shown to enhance cognition and γ oscillatory activity during WM.

Methodology and Principal Findings

We examined the effect of 20 Hz rTMS over the DLPFC on γ oscillatory activity elicited during the N-back task in 24 patients with SCZ compared to 22 healthy subjects. Prior to rTMS, patients with SCZ elicited excessive γ oscillatory activity compared to healthy subjects across WM load. Active rTMS resulted in the reduction of frontal γ oscillatory activity in patients with SCZ, while potentiating activity in healthy subjects in the 3-back, the most difficult condition. Further, these effects on γ oscillatory activity were found to be specific to the frontal brain region and were absent in the parieto-occipital brain region.

Conclusions and Significance

We suggest that this opposing effect of rTMS on γ oscillatory activity in patients with SCZ versus healthy subjects may be related to homeostatic plasticity leading to differential effects of rTMS on γ oscillatory activity depending on baseline differences. These findings provide important insights into the neurophysiological mechanisms underlying WM deficits in SCZ and demonstrated that rTMS can modulate γ oscillatory activity that may be a possible avenue for cognitive potentiation in this disorder.     

Electronically switchable sham transcranial magnetic stimulation (TMS) system

Transcranial magnetic stimulation (TMS) is increasingly being used to demonstrate the causal links between brain and behavior in humans. Further, extensive clinical trials are being conducted to investigate the therapeutic role of TMS in disorders such as depression. Because TMS causes strong peripheral effects such as auditory clicks and muscle twitches, experimental artifacts such as subject bias and placebo effect are clear concerns. Several sham TMS methods have been developed, but none of the techniques allows one to intermix real and sham TMS on a trial-by-trial basis in a double-blind manner. We have developed an attachment that allows fast, automated switching between Standard TMS and two types of control TMS (Sham and Reverse) without movement of the coil or reconfiguration of the setup. We validate the setup by performing mathematical modeling, search-coil and physiological measurements. To see if the stimulus conditions can be blinded, we conduct perceptual discrimination and sensory perception studies. We verify that the physical properties of the stimulus are appropriate, and that successive stimuli do not contaminate each other. We find that the threshold for motor activation is significantly higher for Reversed than for Standard stimulation, and that Sham stimulation entirely fails to activate muscle potentials. Subjects and experimenters perform poorly at discriminating between Sham and Standard TMS with a figure-of-eight coil, and between Reverse and Standard TMS with a circular coil. Our results raise the possibility of utilizing this technique for a wide range of applications.     

Effect of voluntary facilitation on the diaphragmatic response to transcranial magnetic stimulation.

We assessed recruitment curves of the surface diaphragm motor-evoked potential (MEP) after transcranial magnetic stimulation during relaxation and at three different levels of facilitation (20, 40, and 60% of maximal inspiratory esophageal pressure) in 10 healthy subjects (six young and four elderly). MEP amplitude recruitment curves varied between individuals during relaxation and at each level of facilitation. Amplitude recruitment curves during relaxation were reproducible in individual subjects. Inspiratory maneuvers caused a decrease in motor threshold and latency and an increase in MEP amplitude, positively correlated to the intensity of facilitation. These changes were similar in young and elderly subjects. The best fit for MEP amplitude recruitment curves for each condition was obtained with a Boltzmann model. The performance of repeated submaximal inspiratory maneuvers did not affect the amplitude recruitment curves of the relaxed diaphragm. We conclude that the recruitment curve of the diaphragm with transcranial magnetic stimulation is repeatable and changes consistently with facilitation and will, therefore, be a robust experimental tool for the investigation of supraspinal pathways to the diaphragm.     

Post-lesional cerebral reorganisation: Evidence from functional neuroimaging and transcranial magnetic stimulation

Reorganisation of cerebral representations has been hypothesised to underlie the recovery from ischaemic brain infarction. The mechanisms can be investigated non-invasively in the human brain using functional neuroimaging and transcranial magnetic stimulation (TMS). Functional neuroimaging showed that reorganisation is a dynamic process beginning after stroke manifestation. In the acute stage, the mismatch between a large perfusion deficit and a smaller area with impaired water diffusion signifies the brain tissue that potentially enables recovery subsequent to early reperfusion as in thrombolysis. Single-pulse TMS showed that the integrity of the cortico-spinal tract system was critical for motor recovery within the first four weeks, irrespective of a concomitant affection of the somatosensory system. Follow-up studies over several months revealed that ischaemia results in atrophy of brain tissue adjacent to and of brain areas remote from the infarct lesion. In patients with hemiparetic stroke activation of premotor cortical areas in both cerebral hemispheres was found to underlie recovery of finger movements with the affected hand. Paired-pulse TMS showed regression of perilesional inhibition as well as intracortical disinhibition of the motor cortex contralateral to the infarction as mechanisms related to recovery. Training strategies can employ post-lesional brain plasticity resulting in enhanced perilesional activations and modulation of large-scale bihemispheric circuits.     

Influence of transcranial magnetic stimulation on spike-wave discharges in a genetic model of absence epilepsy

Transcranial magnetic stimulation (TMS) impulses, (0.5 Hz, 3 impulses) were presented at threshold intensity to male WAG/Rij rats. One group received stimuli, which involved motor responses of hindlimbs, rats of the second group received sham stimulation. Electrocorticograms (ECoG) were recorded before and up to 2 hr from the moment of transcranial magnetic stimulation. It was established that such stimulation engendered a reduction of spike-wave discharge (SWD) bursts duration. This effect was most pronounced in 30 min from the moment of cessation of stimulation, when a decrease of 31.4% was noted in comparison with sham-stimulated control group. The number of bursts of spike-wave discharges was reduced, but did not reach significant difference when compared both with pre-stimulative base-line level and with sham-stimulated control rats. Bursts of spike-wave discharges restored up to pre-stimulative level in 90-150 minutes from the moment of cessation of transcranial stimulation. It can be concluded that transcranical magnetic stimulation possessed an ability to engender short-time suppression of bursts of spike-wave discharges in WAG/Rij rats.     

Spike suppression in a local cortical circuit induced by transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) noninvasively interferes with human cortical function, and is widely used as an effective technique for probing causal links between neural activity and cognitive function. However, the physiological mechanisms underlying TMS-induced effects on neural activity remain unclear. We examined the mechanism by which TMS disrupts neural activity in a local circuit in early visual cortex using a computational model consisting of conductance-based spiking neurons with excitatory and inhibitory synaptic connections. We found that single-pulse TMS suppressed spiking activity in a local circuit model, disrupting the population response. Spike suppression was observed when TMS was applied to the local circuit within a limited time window after the local circuit received sensory afferent input, as observed in experiments investigating suppression of visual perception with TMS targeting early visual cortex. Quantitative analyses revealed that the magnitude of suppression was significantly larger for synaptically-connected neurons than for isolated individual neurons, suggesting that intracortical inhibitory synaptic coupling also plays an important role in TMS-induced suppression. A conventional local circuit model of early visual cortex explained only the early period of visual suppression observed in experiments. However, models either involving strong recurrent excitatory synaptic connections or sustained excitatory input were able to reproduce the late period of visual suppression. These results suggest that TMS targeting early visual cortex disrupts functionally distinct neural signals, possibly corresponding to feedforward and recurrent information processing, by imposing inhibitory effects through intracortical inhibitory synaptic connections.