P75-T Adaptation of the motor system is associated with neuroplasticity

Background Repetition suppression (RS), i.e., adaption of neural excitability in response to a repeated stimulus, manifests as a decrement in the amplitude of the motor evoked potentials (MEPs) following repeated transcranial magnetic stimulation (TMS) of the motor cortex. RS is associated with abnormal adaptation to external stimuli and may be indicative of neuroplastic capacity. Objective To investigate the association between RS and experimentally induced plasticity. Methods Fourteen healthy subjects (7 males, aged 22–42 years) were studied with a RS paradigm, which was applied prior and following (0 min, 10 min, and 20 min) paired associative stimulation (PAS). The RS paradigm, consisting of twenty trains of four TMS pulses with an inter-stimulus interval (ISI) of 1 s and an inter-train interval (ITI) of 17 s, was applied to abductor pollicis brevis muscle ‘hotspot’. During PAS, median nerve stimulation was delivered 25 ms prior to TMS pulses given at 0.2 Hz for 15 min. Results A two-way repeated ANOVA identified 6 subjects with an interaction effect of RS and PAS ( p p  = 0.05). Conclusion Our results demonstrate that RS is facilitated in subjects showing the interaction effect. This interaction might be mediated by the GABAergic inhibitory system during activation of the negative thalamo-cortical feedback loop due to the homeostatic plasticity.