Mental Simulations and Action Language Are Impaired in Individuals with Aphantasia.

Abstract

Action reading is thought to engage motor simulations, such as those involved during the generation of mental motor images. These simulations would yield modulations in activity of motor-related cortical regions and contribute to action language comprehension. To test these ideas, we measured corticospinal excitability during action reading, and reading comprehension ability, in individuals with normal and impaired imagery (i.e., phantasia and aphantasia, respectively). Thirty-four participants (17 phantasic and 17 aphantasic) were asked to read manual action sentences. By means of TMS, we triggered motor-evoked potentials in the target right index finger. Motor-evoked potential amplitude, a marker of corticospinal excitability, increased during action reading relative to rest for phantasic individuals, but not for aphantasic individuals. This result provides neurophysiological evidence that individuals living with aphantasia present a real neurophysiological deficit in motor system engagement during action reading. Furthermore, deep-level reading comprehension ability was impaired in individuals with aphantasia, who had difficulty selecting words that best fit the context of sentences. Altogether, these findings support the idea that motor simulations, along with the activation within the motor system, contribute to action language comprehension.