Single Magnetic Stimulation Research Articles

Effect of radiofrequency combined with magnetic stimulation on mild and moderate pelvic organ prolapse.

The efficacy of using a single electrical or magnetic stimulation for treating pelvic floor dysfunction is limited. This study aims to investigate the efficacy of radiofrequency combined with magnetic stimulation treatment for mild to moderate pelvic organ prolapse. Patients who completed the treatment in the Third Xiangya Hospital, Central South University were screened, and were divided into 2 groups based on different treatment plans. There were 28 patients who completed magnetic stimulation therapy (the magnetic stimulation therapy group) and 21 patients who completed radiofrequency combined with magnetic stimulation therapy (the combined treatment group). The pelvic organ prolapse quantitation (POP-Q), pelvic floor muscle strength, and pelvic floor ultrasound results were analyzed to assess the efficacy before and after the treatment in both groups, and the POP-Q results of 3 months after the treatment were used to evaluate the maintenance effect of the treatment mode. The POP-Q evaluation results of Aa, Ap, and C points after the treatment in both groups were better than those before the treatment, with statistical significance (all P<0.05). The Aa point POP-Q result of the combined treatment group was better than that of the magnetic stimulation therapy group, with statistical significance (P<0.05). Pelvic floor ultrasound evaluation showed that the bladder neck position during the valsalva maneuver in the combined treatment group was higher than that in the magnetic stimulation treatment group, with statistical significance (P<0.05). The persistence effect of the combined treatment group was long better than that of the magnetic stimulation treatment group, with significant statistical significance (P<0.01). The combined treatment is more effective and has a longer lasting effect than single magnetic stimulation treatment.

Diaphragm Motor-Evoked Potential Induced by Cervical Magnetic Stimulation following Cervical Spinal Cord Contusion in the Rat.

Cervical spinal injury is typically associated with respiratory impairments due to damage to bulbospinal respiratory pathways and phrenic motoneurons. Magnetic stimulation is a non-invasive approach for the evaluation and modulation of the nervous system. The present study was designed to examine whether cervical magnetic stimulation can be applied to evaluate diaphragmatic motor outputs in a pre-clinical rat model of cervical spinal injury. The bilateral diaphragm was monitored in anesthetized rats using electromyogram at the acute, subchronic, and chronic stages following left mid-cervical contusion. The center of a figure-of-eight coil was placed 20 mm caudal to bregma to stimulate the cervical spinal cord. The results demonstrated that a single magnetic stimulation can evoke significant motor-evoked potentials in the diaphragms of uninjured animals when the animal's head was placed 30 mm right or left from the center of the coil. The spontaneous bursting of the diaphragm was significantly attenuated by contusion injury at all-time-points post-injury. However, the threshold of the diaphragmatic motor-evoked potential was reduced, and the amplitude of the diaphragmatic motor-evoked potential was enhanced in response to cervical magnetic stimulation at the acute injury stage. Moreover, the motor-evoked potentials of the bilateral diaphragm in animals with contusions were generally larger when the coil was placed at the left spinal cord at the subchronic and chronic injury stages. These results suggested that cervical magnetic stimulation can be used to examine the excitability of phrenic motor outputs post-injury, and magnetic stimulation applied more laterally may be more effective for triggering diaphragmatic motor-evoked potentials.

P.2.h.012 - Mediterranean diet and mood

We aimed to investigate the influence of high frequency repetitive transcranial magnetic stimulation (rTMS) of the motor cortex on excitability of the masseter inhibitory reflex (MIR) in healthy subjects. Our goal in conducting this study was to obtain a better understanding of the subcortical and cortical networks related to the excitability of the central masticatory pathway.Twenty healthy volunteers participated in this study. MIRs were evaluated both before and after high frequency rTMS to elicit motor evoked potentials (MEPs) using single- and double-shock techniques over the motor cortex. During measurements, the latency and duration of silent periods (SPs) with single magnetic stimulation, and the recovery of SP2 with the double-shock technique, were recorded in basal conditions and immediately after high frequency rTMS. The “real” rTMS condition consisted of 20 stimulus trains delivered at 10 Hz with a 5-s stimulation duration and an intensity of 70% of the active motor threshold (AMT) over the right optimal motor spot for the masseter muscle.were also compared to those obtained after “sham” rTMS 1 week laterUsing the double-shock technique, SP2 recovery time was significantly shorter after high frequency rTMS compared to the basal condition (from 100 to 400 ms; p < 0.001), while at ISIs of 500 and 600 ms, no significant effect was observed (p = 0.084, p = 0.948). There was also no significant change in the SP latency or duration between groups (p > 0.05).High frequency, sub-threshold rTMS of the motor cortex had a facilitative after-effect on the excitability of the MIR. This effect was likely mediated through increased cortical drive to brainstem reflex pathways, which would ultimately accelerate MIR recovery.

Excitability of the masseter inhibitory reflex after high frequency rTMS over the motor cortex: A study in healthy humans

ObjectiveWe aimed to investigate the influence of high frequency repetitive transcranial magnetic stimulation (rTMS) of the motor cortex on excitability of the masseter inhibitory reflex (MIR) in healthy subjects. Our goal in conducting this study was to obtain a better understanding of the subcortical and cortical networks related to the excitability of the central masticatory pathway. MethodsTwenty healthy volunteers participated in this study. MIRs were evaluated both before and after high frequency rTMS to elicit motor evoked potentials (MEPs) using single- and double-shock techniques over the motor cortex. During measurements, the latency and duration of silent periods (SPs) with single magnetic stimulation, and the recovery of SP2 with the double-shock technique, were recorded in basal conditions and immediately after high frequency rTMS. The “real” rTMS condition consisted of 20 stimulus trains delivered at 10Hz with a 5-s stimulation duration and an intensity of 70% of the active motor threshold (AMT) over the right optimal motor spot for the masseter muscle. Resultswere also compared to those obtained after “sham” rTMS 1 week later ResultsUsing the double-shock technique, SP2 recovery time was significantly shorter after high frequency rTMS compared to the basal condition (from 100 to 400ms; p<0.001), while at ISIs of 500 and 600ms, no significant effect was observed (p=0.084, p=0.948). There was also no significant change in the SP latency or duration between groups (p>0.05). ConclusionsHigh frequency, sub-threshold rTMS of the motor cortex had a facilitative after-effect on the excitability of the MIR. This effect was likely mediated through increased cortical drive to brainstem reflex pathways, which would ultimately accelerate MIR recovery.

Effect of muscle length on voluntary activation of the plantar flexors in boys and men.

The aim of the present study was to compare the effect of muscle length on the maximal voluntary activation level (VA) of the plantar-flexors between children and adults. Fourteen boys (10.0±1.0years) and fifteen men (24.6±4.2years) performed 5-s maximal isometric voluntary contractions (MVC) of the plantar-flexor muscles at seven ankle angles [from 10° in dorsi-flexion (DF) to 20° in plantar-flexion (PF); 0°=reference position; the angle between the plantar surface and leg is a right angle]. Single magnetic stimulations were delivered to the posterior tibial nerve during MVCs to determine VA. Results showed a higher absolute torque of the plantar-flexor muscles at long (10° DF) than at short muscle length (20° PF) in men (89.4±19.4 vs. 46.8±17.0Nm, P<0.001) and boys (44.9±18.5 vs. 26.6±12.8Nm, P<0.001). On average, VA was significantly higher in men than in boys (92.4±1.7 vs. 87.6±1.6%, P<0.05). However, no significant main effect of the ankle angle was observed on VA. The VA partly accounts for the plantar-flexors MVC torque difference between children and adults but is not affected by the muscle length changes in both groups. Therefore, VA cannot account for the shape of the torque-angle relationship on the plantar-flexor muscles.

Insights into the Mechanisms of Neuromuscular Fatigue in Boys and Men.

The aim of the present study was to investigate the role of central and peripheral factors in neuromuscular fatigue induced by repeated maximal contractions in children and adults. Eleven boys (9.9 ± 1.2 yr) and 12 men (23.9 ± 3.5 yr) completed a fatigue protocol consisting in a repetition of 5-s maximal isometric voluntary contractions (MVC) of the knee extensors separated by 5-s passive recovery periods until the generated torque reached 60% of its initial value. Single magnetic stimulations were delivered to the femoral nerve every five MVC to follow the course of voluntary activation level and the amplitude of the potentiated twitch torque (Qtw(pot)) and vastus lateralis and rectus femoris concomitant M-waves (Mmax). Torque reached 60% of initial value after 49.5 ± 16.8 and 34.0 ± 19.6 repetitions in boys and men, respectively (P < 0.05). Furthermore, men showed significantly higher knee extensor MVC decline than boys between 50% and 90% of total repetitions (P < 0.05). Voluntary activation remained unchanged in men, whereas it decreased significantly in boys (P < 0.05). In contrast, whereas Qtw(pot) remained unchanged in boys, Qtw(pot) decreased progressively up to 60% of total repetitions in men (P < 0.001). Finally, Mmax remained unchanged for vastus lateralis and rectus femoris muscles in both groups. Children experienced no apparent peripheral fatigue and higher central fatigue than adults. The greater fatigue resistance in children could be related to a strategy of the CNS aimed at limiting the recruitment of motor units to prevent any extensive peripheral fatigue.

Effect of muscle length on voluntary activation level in children and adults.

The aim of the present study was to compare the effect of muscle length on the level of voluntary activation (VA) at short and long muscle lengths between children and adults. Thirteen prepubertal boys (10.2 ± 1.1 yr) and 10 men (23.9 ± 2.9 yr) performed 5-s maximal isometric voluntary contractions of the knee extensor muscles at three muscular angles (20°, 90°, 100°; 0°, full extension) interspersed with at least 60-s passive recovery periods. Single magnetic stimulations were delivered to the femoral nerve during maximal isometric voluntary contractions to determine the level of VA using the twitch interpolation technique. The specific torque was calculated as the absolute torque divided by thigh muscle mass, as assessed using dual-energy x-ray absorptiometry. Finally, the theoretical specific torque that could be produced with a complete (i.e., 100%) activation level (specific torque at 100% VA) was estimated from the values of specific torque and VA. Results showed a higher specific torque in adults at 90° and 100° but not at 20°. Accordingly, VA was significantly higher in adults at 90° (94% ± 4% vs 88% ± 8%, P < 0.05) and 100° (93% ± 6% vs 86% ± 8%, P < 0.05), whereas no significant difference was observed at 20°. Interestingly, the specific torque at 100% VA was not different between groups whatever the joint angle. The lower ability of children to fully activate their motor units at long muscle length could account for their lower specific torque because no difference in theoretical specific torque was observed between groups at 90° and 100°.

Excitability of the central masticatory pathways in patients with sleep bruxism

Since sleep bruxism (SB) is defined as a stereotyped movement and mainly associated with rhythmic masticatory muscle activity, the aim of this study was to get a better understanding on the subcortical and cortical networks related to the excitability of the central masticatory pathways in SB patients. Of 26 SB patients (12 females and 14 males; mean age: 24.9±4.0 years) and 30 normal subjects (18 females and 12 males; mean age: 24.1±3.1 years) selected, the motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) in masseter muscles, and the masseter inhibitory reflex (MIR) elicited by magnetic stimulation with single and double-shock techniques were studied. The MEPs elicited by TMS were similar in both SB patients and normal subjects. As for the MIR elicited by single magnetic stimulation, the latency and duration of the early silent periods (SP1) between the two groups were similar; but in 5 patients the late silent periods (SP2) was absent, and this difference in the frequency of absence of the SP2 between SB patients and normal subjects was significant; with double-shock technique, the recovery of SP2 was significantly lower in SB patients compared to normal subjects. These results suggested an abnormal excitability of the central masticatory in SB patients; and it is also indicated that SB may be mainly under the influence of brainstem networks rather than that of cortical networks.

Noninvasive Determination of Speech Dominance by Single Magnetic Stimulation of the Bilateral Hand Motor Cortex

Magnetic stimulation of the hand area of the motor cortex in both hemispheres was performed at rest and during reading aloud to observe modulated facilitation of hand muscle motor potentials in 6 right-handed patients, with supratentorial lesions but no motor impairment or aphasia, who had undergone the Wada test to determine speech dominance, showing that 5 were left hemisphere dominant and one was bilateral hemisphere dominant. Motor potentials were facilitated during reading aloud in only the right hand in 3 patients, all left hemisphere dominant, greater in the right hand in one, left hemisphere dominant, and greater in the left hand in one patient, bilateral hemisphere dominant. Based on these results we defined a laterality index which was consistent with the Wada test results. Magnetic stimulation may prove useful for determining cerebral dominance, as our method correlates well with the Wada test, and is safe, convenient, and inexpensive.

Motor cortical dysfunction disclosed by single and double magnetic stimulation in patients with fibromyalgia

Objective: To investigate the motor cortex by single and double magnetic stimulation, in patients with fibromyalgia.Methods: Thirteen patients with fibromyalgia and 13 age-matched healthy subjects were examined. We evaluated, in both limbs, motor evoked potential (MEP) latency and amplitude and the MCA/MPA ratio, i.e. MEP cortical amplitude (MCA) /maximal peripheral amplitude of the M response (MPA), the central conduction time (TCC) and the length of the silent period (SP). With double magnetic stimulation, different time intervals between shocks were used: with delays between shocks of 4, 25, 55 and 85 ms, the intensities of the conditioning shock were 80% the relaxed threshold. With delays between shocks of 55, 85, 100, 155, 200, 255 and 355 ms, the intensities of the conditioning shocks were set at 150% the relaxed threshold. In all cases, the intensity of the test shock was 150% the relaxed threshold. The results were also compared with those obtained in 5 women affected by rheumatoid arthritis (RA).Results: As compared to control, the cortical relaxed threshold was enhanced on both sides and limbs (P<0.05). The cortical silent period recorded with single magnetic stimulation was reduced in the upper limbs (P=2.7×10−11) and lower limbs (both sides P=3.6×10−5). The other parameters investigated were normal. With double magnetic stimulation, facilitatory phenomena were absent in fibromyalgic patients and the inhibitory responses recorded with a delay of 155 ms were reduced (P=0.0052). No significant differences were noted between FM and RA patients.Conclusion: This study demonstrated motor cortical dysfunction in patients with fibromyalgia involving excitatory and inhibitory mechanisms. This indicates motor cortical involvement and supports the hypothesis of aberrant central pain mechanisms. The absence of differences between FM and RA suggest that the lesions were not specific and could be related to chronic pain disorders within the central nervous system.

Direct demonstration of the effect of lorazepam on the excitability of the human motor cortex

Objectives: The present study explored the effects of lorazepam, a benzodiazepine with agonist action at the GABAA 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.

Frequency-dependent conduction delay of motor-evoked potentials in multiple sclerosis.

Paired transcranial magnetic stimulation was applied in 33 multiple sclerosis (MS) patients and in 21 healthy controls. A major abnormality was found in latency of the second motor-evoked potential in MS patients. At interstimulus intervals of 75, 100, and 150 ms the central motor conduction time (CMCT) was significantly prolonged in MS patients to 139%, 150%, and 125% of the CMCT of a single magnetic stimulation (P=0.02, P=0.004, P=0.03), respectively. Voluntary contraction of the target muscle abolished the difference in latency independent of the degree of contraction. Stimulation intensity influenced the length of the interstimulus interval during which the maximal conduction delay was obtained. In MS patients there was no correlation between prolonged CMCT to a single magnetic stimulus and the frequency-dependent conduction delay to paired magnetic stimuli. It is hypothesized that the conduction delay of the conditioned response of paired magnetic stimuli in MS is of cortical origin and induced by abnormalities of the ascending volley to the neocortex.