SICI during changing brain states: Differences in methodology can lead to different conclusions

BACKGROUND: Short-latency intracortical inhibition (SICI) is extensively used to probe GABAergic inhibitory mechanisms in M1. Task-related changes in SICI are presumed to reflect changes in the central excitability of GABAergic pathways. Usually, the level of SICI is evaluated using a single intensity of conditioning stimulus so that inhibition can be compared in different brain states. OBJECTIVE: Here, we show that this approach may sometimes be inadequate since distinct conclusions can be drawn if a different CS intensity is used. METHODS: We measured SICI using a range of CS intensities at rest and during a warned simple reaction time task. CONCLUSIONS: Our results show that SICI changes that occurred during the task could be either larger or smaller than at rest depending on the intensity of the CS. These findings indicate that careful interpretation of results are needed when a single intensity of CS is used to measure task-related physiological changes.