Transcranial magnetic stimulation and synaptic plasticity: experimental framework and human models

Interest in the therapeutic potential of non-invasive human brain stimulation has been boosted by an improved understanding of the mechanisms of synaptic plasticity and the stimulus protocols that can induce plasticity in experimental preparations. A range of transcranial magnetic stimulation (TMS) protocols are available that have the potential to mimic these experimental protocols in the human. Repetitive TMS emulates aspects of activity-dependent plasticity, and theta-burst refinements may be able to take into account excitatory and inhibitory networks, paired associative stimulation can extend network considerations to incorporate sensorimotor integration, inhibitory networks may be targeted with short-interval paired stimulation and finally even the precision of spike-timing dependent plasticity may be accessible through I-(indirect) wave dynamics. This review will provide a synthesis of current concepts of activity- and time-dependent plasticity and their homeostatic regulation based on experimental studies, and relate these concepts to the promising range of TMS interventions that are available to target human brain plasticity.