Quadripulse stimulation (QPS) is a newly developed stimulation method to induce neural plasticity in humans. One stimulation burst consisting of four monophasic pulses is given every 5 s for 30 min. A total of 360 bursts (1440 pulses) are given in one session. Short-interval QPS potentiates the target cortical excitability and long-interval QPS depresses it. QPS at an inter-pulse interval of 5 ms (QPS5) induces long-term potentiation (LTP)-like effects most efficiently and QPS50 induces long-term depression (LTD)-like effects most effectively in the primary motor cortex. In this mini-review, we briefly introduce QPS: (i) principle and cortical plasticity (stimulators and protocols, synaptic plasticity, underlying mechanisms, meta-plasticity, axonal plasticity, and drug effects), (ii) robust and strong neural plasticity induction (variability, influence of phasic muscle contraction, independency of BDNF polymorphism, sensory cortical plasticity, neural plasticity in the contralateral hemisphere, on-line effects on the brain networks, studies of normal brain physiology, and visuomotor sequence learning), (iii) therapeutic applications to neurological and psychiatric disorders (Parkinson's disease, epilepsy, cerebrovascular disease, and major depression), (iv) safety, and (v) future issues. Based on this evidence, we propose that QPS is currently the most powerful and reliable non-invasive brain stimulation method to induce neural plasticity in humans.
Keywords: Long-term depression (LTD); Long-term potentiation (LTP); Quadripulse stimulation (QPS); Repetitive transcranial magnetic stimulation (rTMS); Synaptic plasticity.