Quadripulse stimulation – a promising patterned repetitive transcranial magnetic stimulation protocol

Quadripulse stimulation (QPS) is a relatively new and highly promising repetitive transcranial magnetic stimulation protocol. QPS is based on the application of bursts, consisting of 4 monophasic stimuli with a very short interstimulus interval (5 or 50 ms, QPS 5 and QPS50, respectively), which are repeated every 5 seconds. Long-term neuromodulating effects of QPS protocols are bi-directional depending on interstimulus interval: QPS5 increases the excitability of motor cortex while QPS50 decreases it. The main advantage of QPS protocols is a high reproducibility of their effects, which exceeds that of other repetitive transcranial magnetic stimulation protocols. This review discusses the physiological effects and possible mechanisms for inducing neuroplasticity by QPS protocols. Special attention is paid to QPS application in clinical practice both for therapeutic neuromodulation and development of new biomarkers of functional brain state. Available QPS safety data are provided and previous works limitations as well as directions for further studies are analyzed.