Quadripulse transcranial magnetic stimulation (QPS) is an innovative technique of repetitive transcranial magnetic stimulation (rTMS) that can modulate cortical excitability (Kaneko et al., 2020). It involves delivering four bursts of monophasic TMS from four independent magnetic stimulators, with each QPS burst followed by a five-second inter-burst interval (IBI).
A thorough exploration of the inter-stimulus interval (ISI) within a QPS burst revealed that shorter ISIs led to increased motor evoked potential (MEP) amplitudes for a minimum of 75 minutes. Conversely, longer ISIs of 50ms in quadripulse stimulation suppressed MEPs for at least 75 minutes. The efficacy of QPS in modulating cortical excitability appears to be influenced by the inter-burst interval (IBI), with an optimal IBI of approximately 5 seconds (Hanajima et al., 2017).
Compared to other non-invasive brain stimulation protocols, QPS exhibits reduced variability in its after-effects. Approximately 80% of younger participants demonstrate effects of QPS-50ms, with 69% displaying a measurable response through changes in MEPs (Hanajima et al., 2017; Nakamura et al., 2017). The reliability of QPS in modulating cortical excitability seems to stem from its utilisation of repetitive monophasic pulses instead of biphasic pulses.
In a systematic comparison between monophasic and biphasic quadripulse QPS protocols with identical parameters, it was observed that the increases in motor MEP amplitude induced by QPS-5ms, and the decreases induced by QPS-50ms were greater when monophasic pulses were employed rather than biphasic pulses (Hamada et al., 2007).
Monophasic pulses not only generate larger effects on the MEP but also exhibit sustained effects that persist beyond one hour. The utilisation of monophasic pulses in QPS may contribute to the reduced variability observed compared to other biphasic rTMS protocols. It also accounts for a higher number of responders following QPS application.
Kimura et al., (2022) examined the effects of a newly developed QPS stimulator called DuoMAG MP-Quad and found that it was effective in inducing the desired after-effects. The study involved thirteen healthy participants who underwent two sessions of QPS using different parameters. The results showed significant modulation of motor evoked potentials (MEPs) after QPS, with QPS5 producing enlargement of MEPs and QPS50 resulting in reduction. The findings confirm the effectiveness of QPS in modulating brain activity and suggest that the newly developed stimulator is a promising tool for further research and treatment.
(A) Excitatory QPS5-IBI2.5 (red circle) did not cause any changes in MEP sizes. However, excitatory QPS5-IBI5 (filled red circle) facilitated MEPs.
(B) Inhibitory QPS50-IBI2.5 (blue circle) had no effect on MEP sizes, whereas inhibitory QPS50-IBI5 (filled blue circle) suppressed MEPs.
(C) Excitatory QPS5-IBI5 (red filled circle) and excitatory QPS5-IBI7.5 (red diamond) showed similar time courses, but variable responses were observed with excitatory QPS5-IBI7.5. No changes in MEP sizes were found with excitatory QPS5-IBI10 (red square).
(D) Inhibitory QPS50-IBI5 (blue filled circle) consistently decreased MEP sizes, but inhibitory QPS50-IBI7.5 (blue diamond) and inhibitory QPS50-IBI10 (blue square) had lesser effects. Error bars represent standard error.
(E, F) Excitatory QPS5-monophasic (red filled circle), excitatory QPS5-biphasic (red triangle), inhibitory QPS50-monophasic (blue filled circle), and inhibitory QPS50-biphasic (blue triangle) were compared. Biphasic QPS had a shorter duration of effect than monophasic QPS.
Error bars indicate standard error. The timing of QPS is indicated by the black arrow in all figures.
- Quadro-pulse stimulation is more effective than paired-pulse stimulation for plasticity induction of the human motor cortex. Hamada, M. et al. Clinical Neurophysiology 118(12): 2672-2682. (2007)
- The effect of age on the homotopic motor cortical long-term potentiation-like effect induced by quadripulse stimulation. Hanajima, R. et al. Experimental Brain Research 235: 2103-2108. (2017)
- Region-dependent bidirectional plasticity in M1 following quadripulse transcranial magnetic stimulation in the inferior parietal cortex. Kaneko, F., Shibata, E. and Okawada, M., et al. Brain Stimulation 13(2): 310-317. (2020)
- Quadripulse stimulation: a replication study with a newly developed stimulator. Kimura, I., Ugawa, Y., Hayashi, M.J. and Amano, K. Brain Stimulation 15(3): 579-581. (2022)
- Variability in response to quadripulse stimulation of the motor cortex. Nakamura, K. et al. Brain Stimulation 9(6): 859-866. (2016)
- Effects of the motor cortical quadripulse transcranial magnetic stimulation (QPS) on the contralateral motor cortex and interhemispheric interactions. Tsutsumi, R. et al. J Neurophysiol 111(1): 26-35. (2014)
The following products from our catalogue are associated with this technique. To find out more about these supported devices, follow the links below or get in touch via email or phone.