Exploring the impact of sentential negation on inhibitory motor networks: Insights from paired-pulse TMS

The embodied approach to language meaning suggests that negation with action verbs decreases activation of the negated concept, reflected in reduced motor-evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS). This study aims to explore how action negation influences inhibitory and facilitatory mechanisms within the primary motor cortex (M1) using paired-pulse TMS (ppTMS). We evaluated corticospinal excitability (CSE), short intracortical inhibition (SICI), indexing GABAA activity, and intracortical facilitation (ICF), related to glutamatergic activity. Participants read action and attentional sentences, presented in affirmative and negative form, with TMS pulses administered over the left M1 at 250 ms from verb onset. Results show negated action sentences differently modulate CSE and SICI compared to affirmative ones, indicating GABAA activity of negation. No differences emerged for attentional sentences, nor for ICF stimulation. This study confirms the suppressive impact of action negation on CSE and highlights inhibitory networks' role in action negation processing within M1.