A systematic review of the effect of pulse parameters of next-generation TMS devices on corticospinal excitability and neuroplasticity

BACKGROUND: Conventional TMS devices are limited in the number of variations of pulse parameters they produce, which limits the extension of TMS application. Recently, however, successful attempts have been made to introduce next-generation (next-gen) TMS devices with adjustable pulse parameters. Although research using these devices is still in its infancy, a systematic synthesis of the direction of results is valuable to identify the current progress and some limitations of these technologies which can guide further studies in the field. OBJECTIVE: This review aims to investigate the influence of pulse parameters (width, shape, and current direction) of next-gen TMS devices on corticospinal excitability and the induction of neuroplasticity. METHODS: Using the PRISMA method of reporting systematic reviews, we searched major biomedical databases - PubMed (n = 84), Web of Science (n = 141), Scopus (n = 111) and APA PsychInfo (n = 27) for literature, with 21 studies included in this review. RESULTS: Compared to conventional TMS devices, next-generation TMS devices were more efficient in many neurophysiological measurements. For plasticity inducing protocols, both inhibitory and facilitatory protocols showed enhanced respective inhibitory and excitatory after-effects with increasing pulse width. The new near-rectangular pulse shape moreover induced stronger inhibitory after-effects compared to conventional pulses. CONCLUSIONS: Next-generation devices expand the parameter space of TMS. Further studies are however needed to explore the full potential of these next-gen devices, especially in non-motor brain regions. SIGNIFICANCE: Next-gen TMS devices do hold a promise in the optimization of the neuromodulatory effects of TMS.