Common (and multiple) neural substrates for static and dynamic motion after-effects: A rTMS investigation

INTRODUCTION Prolonged exposure to directional motion (adaptation) biases the perceived direction of subsequently presented test stimuli towards the opposite direction with respect to that of adaptation (i.e., motion after-effect; MAE). Different neural populations seem to be involved in the generation of the MAE, depending on the spatiotemporal characteristics of both adapting and test stimuli. Although the tuning mechanisms of the neural populations involved in the MAE have been psychophysically identified, the specific loci along the motion processing hierarchy where the different types of MAE take place is still debated. METHOD In this study, by using repetitive transcranial magnetic stimulation (rTMS) delivered during the inter-stimulus interval (ISI) between adapting and test patterns, we investigated the cortical locus of processing of static MAE (sMAE) and dynamic MAE (dMAE). RESULTS Results showed that rTMS over V2/V3 or V5/MT decreased the perceived duration of both sMAE and dMAE, although rTMS over V2/V3 decreased mainly the perceived duration of sMAE. CONCLUSIONS sMAE and dMAE rely on the same cortical structures present at intermediate and low-levels of motion processing, although low-level visual areas (e.g., V2/V3) show a prevalence of neurons responsible for sMAE.