Quadripulse transcranial magnetic stimulation (QPS) is a novel repetitive transcranial magnetic stimulation (rTMS) technique that can be used to increase or decrease cortical excitability1. Four bursts of monophasic TMS, originating from four separate magnetic stimulators, are administered, with each QPS burst being separated by an inter-burst interval (IBI) of ﬁve seconds.
In a comprehensive investigation of the inter-stimulus interval (SI) which separates each TMS pulse within a QPS burst, shorter ISIs were found to increase the amplitude of motor evoked potentials (MEPs) for up to at least 75 minutes while, in contrast, quadripulse stimulation at longer ISIs of 50ms suppressed MEPs for at least 75 minutes. The success of QPS at modulating cortical excitability appears to be determined by the IBI, with an IBI of around 5 seconds appearing to be optimal2.
The variability of QPS after-eFFects are smaller relative to other non-invasive brain stimulation protocols, with 80% of younger participants showing effects of QPS-50ms and 69% of participants showing a response as measured by a change in MEP3,4. The success of QPS as a reliable means of altering cortical excitability appears to be due to the use of repetitive monophasic pulses instead of biphasic pulses.
A systematic comparison of monophasic and biphasic QPS protocols that were otherwise identical revealed that QPS-5ms-induced increases and QPS-50ms-induced decreases in MEP amplitude were greater when monophasic pulses were used compared to biphasic pulses5.
Not only do monophasic pulses produce larger eﬀects on the MEP, but the monophasic pulses also produce effects that do not return to baseline within an hour. The use of monophasic pulses may be a potential reason for the reduced variability of QPS compared to other biphasic rTMS protocols, and for a high number of responders after the application of QPS6.
- Quadro-pulse stimulation is more effective than paired-pulse stimulation for plasticity induction of the human motor cortex.. Hamada M., Hanajima R., Terao Y., Arai N., Furubayashi T., Inomata-Terada S., Yugeta A., Matsumoto H., Shirota Y., Ugawa Y.. Clinical Neurophysiology, 118.. (December 2007), pp. 2672-2682.
- Variability in Response to Quadripulse Stimulation of the Motor Cortex.. Nakamura, K., Grouss S J., Hamada M., Enomoto H., Kadowaki S., Abe M., Murakami T., Wiratman W., Chang F., Kobayashi S., Hanajima R., Terao Y., Ugawa Y.. Brain Stimulation, 9.. (December 2016), pp. 859-866.
- Effects of the motor cortical quadripulse transcranial magnetic stimulation (QPS) on the contralateral motor cortex and interhemispheric interactions.. Tsutsumi R., Hanajima R., Terao Y., Shirota Y., Ohminami S., Shimizu T., Tanaka N., Ugawa Y.. J Neurophys, 111.. (January 2014), pp. 26-35.
- The effect of age on the homotopic motor cortical long-term potentiation-like effect induced by quadripulse stimulation.. Hanajima R., Tanaka N., Tsutsumi R., Enomoto H., Abe M., Nakamura K., Kobayashi S., Hamada M., Shimizu T., Terao Y., Ugawa Y.. Experimental Brain Research, 235.. (July 2017), pp. 2103-2108.
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