Negation plays an important role in language, changing the meaning of sentences and the focus of our attention. Recent studies suggest that understanding non-action sentences, such as "She did not write the letter", involves brain areas responsible for movement control. In this context, Alessio Avenanti and collaborators investigated how reading affirmative and negative action and attention sentences affects inhibitory and facilitatory mechanisms in the primary motor cortex (M1), which controls movements.
Using a technique called transcranial magnetic stimulation (TMS), they discovered that negated action sentences (like "did not write") decrease activity in the brain's motor areas, blocking action. However, non-action sentences, such as "She was not attentive", do not have this effect. Negated action sentences also reduce the activity of inhibitory circuits in the brain, regulated by the neurotransmitter GABAA, but do not affect circuits that facilitate brain activity.
These findings help us better understand how the brain processes language and how this is connected to the movements we perform. This study was supported by the BIAL Foundation, in the scope of the research project 304/22 - Boosting and hindering action imitation by modulating spike-timing dependent plasticity, and published in the journal Brain and Language, in the article Exploring the impact of sentential negation on inhibitory motor networks: Insights from paired-pulse TMS.
ABSTRACT
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.
