Online corticomotor modulations in action inhibition: Insights from TMS studies

Effective response inhibition is crucial for daily functioning. Behavioural inhibition can be assessed using the Stop Signal Task (SST), which requires coordinated activation across a complex network of brain regions, ultimately modulating corticospinal excitability (CSE). Importantly, CSE is not only modulated by excitatory drive but also by intracortical inhibitory processes such as short intracortical inhibition (SICI), which reflects the inhibitory activity of the GABAA receptors within the primary motor cortex. This review examines a series of studies exploring CSE changes, measured through Transcranial Magnetic Stimulation (TMS) applied online, i.e., during SST performance. We mainly focused on the temporal dynamics of CSE and SICI during the SST across healthy and clinical populations, highlighting differences between task-related and unrelated muscles, examining both global and selective modulations in proactive and reactive versions of the SST. Our discussion addresses the methodological and theoretical considerations involved in recording CSE online and questions the SST's effectiveness in accurately capturing inhibitory processes. Additionally, we analyse findings from motor-related disorders in clinical populations to identify specific abnormalities in CSE modulation and their underlying neural mechanisms. By summarizing the existing literature, we aim to offer a comprehensive view of the temporal dynamics of CSE, identifying key factors and methodologies that influence CSE modulation. This review seeks to prompt future directions in cognitive neuroscience research and potential clinical applications.