Executing and imagining transitive and intransitive gestures: electrophysiological (RP) and optical imaging (fNIRS) evidences

Action planning and execution processes have been explored by many neuroanatomical, electrophysiological and functional studies. It is known that a complex network of neural structures is responsible for voluntary action intentionalization and production, including the Supplementary Motor Area (SMA) and pre-Supplementary Motor Area (preSMA), the Premotor Cortex (PMC), the primary motor cortex (M1), the Anterior Cingulate Cortex (ACC), and subcortical structures. Again, electrophysiological research identified specific markers of action planning processes – namely the Readiness Potential (RP) and its subcomponents. Nonetheless, the interplay between neural structures, networks and processes for the transition from motor planning and preparation to proper movement initiation and guidance is still a matter of debate, as is the relationship between structures supporting those phases. The present study then aimed at exploring cortical correlates of motor planning and production and their relationship by taking advantage of an integrated electrophysiological-hemodynamic methodology which capitalized on electroencephalography (EEG) high time resolution and functional Near-Infrared Spectroscopy (fNIRS) high spatial resolution. We compared participants (N = 15) during planning and execution or imagination of complex hand gestures. Videos depicting target gestures were presented at the beginning of each experimental trial, half of them were transitive (i.e. they implied the use of an object – such as painting with a brush) and the other half were intransitive (i.e. they did not involved object-use while still being meaningful – such as waving to greet someone). The analysis of electrophysiological markers of the planning phase revealed that comparable RPs occurred before gesture execution and imagination, with an interesting “facilitation effect” (anticipated latency) for transitive gestures in particular for motor imagination. The analyses of fNIRS markers (oxygenated haemoglobin concentration) of the execution/imagination phases revealed that while the SMA was similarly activated during execution and imagination of transitive/intransitive gestures, the PMC was particularly involved in execution processes and the posterior parietal cortex was peculiarly involved in transitive gesture execution. Finally, integrated regression analyses showed that the RP component may be deemed as a predictive factor of subsequent hemodynamic brain activity during action production and that the relationship was different across sensorimotor regions depending on task and gesture type.