Poster B83, Sunday, March 26, 8:00 – 10:00 am, Pacific Concourse
tDCS to premotor cortex changes action verb understanding: Complementary effects of inhibitory and excitatory stimulation
Tom Gijssels1,2, Richard B. Ivry3, Daniel Casasanto1; 1University of Chicago, 2Vrije Universiteit Brussel, Belgium, 3University of California, Berkeley
Do neural systems for planning motor actions play a functional role in understanding action language? Across multiple neuroimaging studies, processing action verbs correlates with somatotopic activity in premotor cortex (PMC). Yet, only one neurostimulation study supports a functional role for PMC in action verb understanding: paradoxically, continuous theta-burst TMS over left PMC, a protocol assumed to disrupt processing, made people respond faster to action verbs. Here we investigated the effect of PMC excitation or inhibition on action verb understanding using transcranial Direct Current Stimulation (tDCS). Right-handers received bilateral stimulation to PMC hand areas, either exciting left PMC (anode placed over left PMC, cathode over right PMC) or inhibiting left PMC (electrode placement reversed). Then, participants made lexical decisions on unimanual action verbs and abstract verbs. tDCS polarity selectively affected response accuracy to unimanual action verbs. Inhibitory left PMC stimulation caused a relative improvement in performance for right-hand responses, consistent with our cTBS results, whereas excitatory left PMC stimulation caused a relative impairment. tDCS polarity did not differentially affect responses to abstract verbs. These complementary effects of exciting and inhibiting left PMC suggest that action language understanding does not depend on “all-or-nothing” activation of PMC, but rather relies on a complex balance of neural excitation and inhibition. Previous neurostimulation results showed that modulating PMC activity can influence how fast people respond to action verbs. The present results show that modulating PMC activity also affects how well people process action verbs, strengthening the evidence that motor simulations contribute to understanding action language.
Topic Area: LANGUAGE: Semantic