Masakuni Iwahashi

Frequency-dependent effects of repetitive transcranial magnetic stimulation on the human brain.

The aim of this study was to examine the effects of repetitive transcranial magnetic stimulation (rTMS) on human brain activity. The effects of low-frequency magnetic stimulation were evaluated by analyzing the P300 component of event-related potentials (ERPs). A figure eight-shaped flat coil was used to stimulate the region over the left or the right supramarginal gyrus, which is considered to be the origin of the P300 component. We examined the effect of rTMS on the latency of the P300 component in 14 healthy individuals by applying 100 magnetic pulses for each stimulus point. Stimulus frequencies were 1.00, 0.75, 0.50, and 0.25 Hz rTMS. The auditory oddball task was used to elicit the P300s before and shortly after rTMS. We found that P300 latencies varied according to the stimulation frequency and the hemisphere of rTMS application. A 1.00 Hz rTMS pulse train over the left supramarginal gyrus shortened the P300 latencies by ∼15 ms at Fz. A 0.5 Hz rTMS pulse train over the left supramarginal gyrus lengthened the P300 latencies by ∼15 ms at Fz. In contrast, 0.75 and 0.25 Hz rTMS pulse trains over the left supramarginal gyrus and 1.00, 0.75, 0.50, and 0.25 Hz rTMS pulse trains over the right supramarginal gyrus did not alter P300 latencies. These results indicate that rTMS frequency affects cognitive processing. We suggest that the effects of rTMS vary according to the activity of excitatory and inhibitory synapses. In addition, the effects of rTMS over the left supramarginal gyrus are dependent on stimulus frequency.

Time-dependent effects of low-frequency repetitive transcranial magnetic stimulation of the supramarginal gyrus

In this paper, we report our studies of the effects of stimulating the bilateral supramarginal gyrus (SMG) with low-frequency transcranial magnetic stimulation (rTMS) or short-term rTMS on brain excitability in humans. We analyzed the effects of various durations of stimulation on P300 latencies of the event-related potential (ERP). Magnetic pulses were delivered using a figure-eight flat coil. The intensity of rTMS was set to 80% of the subjects motor threshold. In each round of rTMS, 100 magnetic pulses were applied over the scalp at frequencies of 1.00, 0.75, and 0.50 Hz. ERPs were measured prior to magnetic stimulation as a control. The effects of magnetic stimulation were then determined by measuring its effects on P300 latencies elicited by an odd-ball task. These latencies were measured before and 0, 5, 10, and 15 min after the magnetic stimulation. 1.00 Hz low-frequency rTMS of the left SMG decreased P300 latencies for approximately 10 min. In contrast, 0.50 Hz rTMS of the left SMG resulted in delayed P300 latencies for approximately 15 min. We furthermore found that 0.75 Hz rTMS of the left SMG and 1.00, 0.75 and 0.5 Hz rTMS of the right SMG did not affect P300 latencies. These results suggest that the duration of the effects of rTMS depend on the frequency of stimulation.

Basic study on the influence of inhibition induced by the magnetic stimulation on the peripheral nerve

The purpose of this study is to analyze the inhibition mechanism of magnetic stimulation on motor function. A magnetic stimulator with a flat figure-eight coil was used to stimulate the peripheral nerve of the antebrachium. The intensity of magnetic stimulation was 0.8 T, and the stimulation frequency was 1 Hz. The amplitudes of the motor-evoked potentials (MEPs) at the abductor pollicis brevis muscle and first dorsal interosseous muscle were used to evaluate the effects of magnetic stimulation. The effects of magnetic stimulation were evaluated by analyzing the MEP amplitude before and after magnetic stimulation to the primary motor cortex. The results showed that MEP amplitude after magnetic stimulation compared with before magnetic stimulation decreased. Because there were individual differences in MEP amplitude induced by magnetic stimulation, the MEP amplitude after stimulation was normalized by the amplitude of each participant before stimulation. The MEP amplitude after stimulation decreased by app...

Modulation of amplitude and latency of motor evoked potential by direction of transcranial magnetic stimulation

The present study analyzed the effects of monophasic magnetic stimulation to the motor cortex. The effects of magnetic stimulation were evaluated by analyzing the motor evoked potentials (MEPs). The amplitude and latency of MEPs on the abductor pollicis brevis muscle were used to evaluate the effects of repetitive magnetic stimulation. A figure eight-shaped flat coil was used to stimulate the region over the primary motor cortex. The intensity of magnetic stimulation was 120% of the resting motor threshold, and the frequency of magnetic stimulation was 0.1 Hz. In addition, the direction of the current in the brain was posterior-anterior (PA) or anterior-posterior (AP). The latency of MEP was compared with PA and AP on initial magnetic stimulation. The results demonstrated that a stimulus in the AP direction increased the latency of the MEP by approximately 2.5 ms. MEP amplitude was also compared with PA and AP during 60 magnetic stimulations. The results showed that a stimulus in the PA direction graduall...

Alteration of the Motor Cortex Excitability by Modulation of the Stimulus Parameter of Peripheral Stimulation

Transcranial magnetic stimulation (TMS) is known to elicit a conditioning effect on cortical excitability. The purpose of this study was to investigate changes in cortical excitability induced by peripheral stimulation with differing frequency and stimulation site. A magnetic stimulator with a flat figure-eight coil was used for TMS and was performed on the left primary motor cortex. The electrical stimulation and magnetic stimulation were used in peripheral stimulation and the stimulus sites were the right and left supination of the forearm. Peripheral stimulation was performed at a stimulus frequency of 1 Hz or 10 Hz. Alterations of cortical excitability induced by peripheral stimulation were evaluated by comparing the mean of the motor evoked potential amplitude elicited by TMS each before and after peripheral stimulation. We found that cortical excitability varied according to the stimulation site and frequency in both the electrical and magnetic stimulation over the forearm. The inhibition of cortical excitability was observed in both 1 Hz electrical and magnetic stimulation over the right forearm. In contrast, the facilitation of cortical excitability was observed at 1 Hz electrical and magnetic stimulation over the left forearm, and it was confirmed for both the right and left forearms at 10 Hz electrical and magnetic stimulation. Moreover, regarding the alteration of cortical excitability induced by peripheral stimulation, it was confirmed that magnetic stimulation has more the significant difference than electrical stimulation. We suggest that peripheral stimulation by electrical and magnetic stimulation have a similar effect to TMS, and can induce both facilitation and inhibition of cortical excitability. Moreover, in the case of peripheral stimulation of the same stimulus frequency, we expect that the magnetic stimulation has more the significant effect than electrical stimulation to cortical excitability.

Modulation of motor cortex excitability by peripheral magnetic stimulation of different stimulus sites and frequencies

Peripheral stimulation is known to influence the state of cortical excitability. The purpose of this study is to investigate whether peripheral magnetic stimulation has similar effects on cortical excitability to transcranial magnetic stimulation (TMS). A magnetic stimulator with a flat figure-of-eight coil was used for both TMS, and peripheral magnetic stimulation applied to the bilateral forearms. TMS was performed on the left primary motor cortex to evaluate influence of the peripheral magnetic stimulation, and motor evoked potential (MEP) was measured from the right first dorsal interosseous. Peripheral magnetic stimulation was performed at a stimulus frequency of 1 Hz or 10 Hz, to the stimulus sites on the right and left supination of the forearm. The effects of peripheral magnetic stimulation were evaluated by comparing the mean MEP amplitude elicited by TMS before and after peripheral magnetic stimulation. We found that cortical excitability varied according to the stimulation site and frequency of the peripheral magnetic stimulation. The inhibition of cortical excitability was observed following 1 Hz peripheral magnetic stimulation over the right forearm (p<;0.001). In contrast, increased cortical excitability was observed using 1 Hz peripheral magnetic stimulation over the left forearm and 10 Hz stimulation over either the right or left forearms. We suggest that peripheral magnetic stimulation has a similar effect to TMS, and can induce both facilitation and inhibition of cortical excitability.

Change of Cognition Effects by Impact of the Transcranial Magnetic Stimulation

The purpose of this paper is to investigate the effects of sub- or supra-threshold low-frequency repetitive transcranial magnetic stimulation (rTMS) on cognitive function. The magnetic stimulation was delivered at 1 Hz to the left supramarginal gyrus, which is considered to be the area of origin of the P300 event-related potential component. The intensity of magnetic stimulation was 80% or 120% of motor threshold, and 100 magnetic pulses were applied. The auditory oddball task, consisting of tone burst waves, was used to elicit P300 before and shortly after magnetic stimulation. We found that P300 latency depended on the intensity of the 1 Hz magnetic stimulation. With subthreshold rTMS, P300 latency was significantly shortened compared with before magnetic stimulation by around 10 ms (Cz: p<;0.05) on average. With the suprathreshold rTMS, the latency was significantly delayed compared with before magnetic stimulation by around 10 ms (Cz: p<; 0.01) on average. The facilitation of cortical excitability by rTMS may induce the shortening of P300 latency, whereas the inhibition of cortical excitability may induce its delay. Thus, P300 latency can be altered by both sub- and supra-threshold low-frequency magnetic stimulation.

The impact of rTMS over the dorsolateral prefrontal cortex on cognitive processing

The purpose of the present study was to use event-related potentials (ERP) to clarify the effect of magnetic stimulation on cognitive processing. A figure eight-shaped flat repetitive transcranial magnetic stimulation (rTMS) coil was used to stimulate either the region over the left or the right dorsolateral prefrontal cortex, which is considered to be the origin of the P300 component. Stimulus frequencies were 1.00, 0.75 and 0.50 Hz rTMS. The strength of the magnetic stimulation was set at 80% of the motor threshold for each participant. The auditory oddball task was used to elicit P300s before and shortly after rTMS, and comprised a sequence of sounds containing standard (1 kHz pure tone, 80% of trials) and deviant (2 kHz pure tone, 20% of trials) stimuli. We found that a 1.00 Hz rTMS pulse train over the left dorsolateral prefrontal cortex increased P300 latencies by 8.50 ms at Fz, 12.85 ms at Cz, and 11.25 ms at Pz. In contrast, neither 0.75 and 0.50 Hz rTMS pulse trains over the left dorsolateral prefrontal cortex nor 1.00, 0.75 and 0.50 Hz rTMS pulse trains over the right dorsolateral prefrontal cortex altered P300 latencies. These results indicate that rTMS frequency affects cognitive processing. Thus, we suggest that the effects of rTMS vary according to the activity of excitatory and inhibitory neurons in the cerebral cortex.

Effects of low-frequency repetitive transcranial magnetic stimulation on event-related potential P300

The present study analyzed the effects of repetitive transcranial magnetic stimulation (rTMS) on brain activity. P300 latency of event-related potential (ERP) was used to evaluate the effects of low-frequency and short-term rTMS by stimulating the supramarginal gyrus (SMG), which is considered to be the related area of P300 origin. In addition, the prolonged stimulation effects on P300 latency were analyzed after applying rTMS. A figure-eight coil was used to stimulate left-right SMG, and intensity of magnetic stimulation was 80% of motor threshold. A total of 100 magnetic pulses were applied for rTMS. The effects of stimulus frequency at 0.5 or 1 Hz were determined. Following rTMS, an odd-ball task was performed and P300 latency of ERP was measured. The odd-ball task was performed at 5, 10, and 15 min post-rTMS. ERP was measured prior to magnetic stimulation as a control. Electroencephalograph (EEG) was measured at Fz, Cz, and Pz that were indicated by the international 10–20 electrode system. Results demonstrated that different effects on P300 latency occurred between 0.5–1 Hz rTMS. With 1 Hz low-frequency magnetic stimulation to the left SMG, P300 latency decreased. Compared to the control, the latency time difference was approximately 15 ms at Cz. This decrease continued for approximately 10 min post-rTMS. In contrast, 0.5 Hz rTMS resulted in delayed P300 latency. Compared to the control, the latency time difference was approximately 20 ms at Fz, and this delayed effect continued for approximately 15 min post-rTMS. Results demonstrated that P300 latency varied according to rTMS frequency. Furthermore, the duration of the effect was not similar for stimulus frequency of low-frequency rTMS.The present study analyzed the effects of repetitive transcranial magnetic stimulation (rTMS) on brain activity. P300 latency of event-related potential (ERP) was used to evaluate the effects of low-frequency and short-term rTMS by stimulating the supramarginal gyrus (SMG), which is considered to be the related area of P300 origin. In addition, the prolonged stimulation effects on P300 latency were analyzed after applying rTMS. A figure-eight coil was used to stimulate left-right SMG, and intensity of magnetic stimulation was 80% of motor threshold. A total of 100 magnetic pulses were applied for rTMS. The effects of stimulus frequency at 0.5 or 1 Hz were determined. Following rTMS, an odd-ball task was performed and P300 latency of ERP was measured. The odd-ball task was performed at 5, 10, and 15 min post-rTMS. ERP was measured prior to magnetic stimulation as a control. Electroencephalograph (EEG) was measured at Fz, Cz, and Pz that were indicated by the international 10–20 electrode system. Results de...

Frequency Dependence of P300 Latency by Low-Frequency Repetitive Transcranial Magnetic Stimulation

The aim of this study was to investigate the effects of repetitive transcranial magnetic stimulation (rTMS) on brain activity. The latency of the P300 component of the event-related potential (ERP) was used to evaluate the effects of low-frequency and short-term rTMS on brain activity. We investigated the effects of rTMS on P300 latencies by stimulating the supramarginal gyrus (SMG), which is considered to be the area of origin of the P300. As the frequency-dependence of low-frequency rTMS has not been previously investigated in detail, we evaluated the effects of rTMS at frequencies of 1, 0.75 or 0.5 Hz on P300 latencies. The odd-ball task was used to elicit P300s before and shortly after the scalp was stimulated by rTMS. Electroencephalography recordings were measured at the Fz, Cz and Pz electrodes, which were based on the international 10-20 electrode system. We found that 1, 0.75 and 0.5 Hz rTMS affected P300 latencies. 1 Hz rTMS of the left SMG shortened P300 latencies by approximately 25 ms at the Cz compared with the P300 latencies before rTMS. 0.5 Hz rTMS of the left SMG lengthened P300 latencies by approximately 20 ms at the Cz compared with the P300 latencies before rTMS. In contrast, 0.75 Hz rTMS of the left SMG did not affect P300 latencies. These results demonstrate that P300 latencies vary according to the frequency of rTMS.