P52-S State-dependent changes in cortical reactivity: comparison between direct cortical and peripheral stimulation

Introduction Peripheral as well as direct cortical stimulations have been classically used to probe the reactivity of thalamocortical circuits across brain states, showing consistent state-dependent modifications. Methods Here we aim at directly comparing state-dependent changes across the wake/sleep cycle of the electroencephalographic (EEG) responses to transcranial magnetic stimulation (TMS – applied over premotor and parietal areas) and to electrical median nerve stimulation (EMNS - applied at an intensity able to reproducibly elicit thumb movements) in two groups of 8 healthy individuals each. Results By tuning stimulation parameters, we roughly equalized the strength of brain activation elicited by TMS and EMNS during wakefulness and achieved a similar ( p  = 0.8) overall (0–600 ms) global mean field power (GMFP). The time-course of wakefulness GMFP significantly peaked ( p p Conclusions Despite a common reduction of complexity during sleep, brain activation elicited by the two stimulation approaches reveals different state-dependent changes, highlighting the presence of cortical bistability in the case of TMS and of subcortical gating in the case of EMNS.