S15-3. Why is theta burst stimulation effective?

Abstract

As the first patterned protocol of repetitive transcranial magnetic stimulation (rTMS), theta burst stimulation (TBS) gives bursts containing 3 pulses at 50 Hz at 5 Hz in either an uninterrupted continuous train (continuous TBS, cTBS) or short trains with pauses in between (intermittent TBS, iTBS). TBS induces a cortical modulation effect outlasting the stimulation for up to an hour after 20–192 s of stimulation. Since TBS is usually given at a low intensity for a short period of time, coil overheat is rarely seen before the end of stimulation. Moreover, TBS is convenient to use because only a single set of rTMS machine is required for producing all TBS protocols. The development of TBS is based on the firing pattern in the hippocampus of animals. Similar electrical stimulation has been used for inducing long-term potentiation type of neuroplasticity in animal. In line with the animal protocol, several evidences suggest that the effects of TBS are induced through mechanisms of synaptic plasticity. Following the plasticity mechanism, a theoretical model was built to explain how the stimulation pattern is crucial for determining the polarity of after-effect induced by TBS. All these explain why TBS is effective in modulating the cortical excitability in human.