Planning and performance of hand gestures: predictive role of Readiness Potential on cerebral hemodynamic response (fNIRS)

Several neuroanatomical and functional studies have explored cortical correlates of action planning and production. However, the role of specific cortical areas and the processes underpinning the transition between these two interconnected phases have been scarcely analyzed. The aim of the present study was therefore to examine cortical correlates of motor planning and motor production of hand gesture. Using electrophysiological (EEG) and functional Near-Infrared Spectroscopy (fNIRS) measures, we investigated the relationship between gesture planning and gesture production in different tasks performances, i.e. execution and imagination. In addition, we directly compared meaningful gestures involving an object (transitive actions) and without (intransitive actions). Electrophysiological modulations (Readiness Potential) and hemodynamic responses (O2Hb concentration, d values) were analyzed. More specifically, we studied the predictive role of EEG on brain activity considering the relationship between RPs during gesture planning as well as cortical hemodynamic responses during gesture production. Participants were instructed to observe videos showing gestures, then to perform the same gestures, and eventually to only imagine performing them. Transitive and intransitive gesture categories were created from a selected dataset of stimuli, validated by twenty-eight judges based on familiarity, frequency, complexity, and, for transitive gesture category, objects function and handiness of the object involved. The analysis of the planning phase demonstrated that both gesture execution and imagination were preceded by similar RP. Specifically, RP were anticipated in case of transitive gestures, particularly for motor imagination. Moreover, the analysis of O2Hb concentration reveals higher O2Hb level during execution tasks as compared to imagination tasks. Indeed, while SMA was similarly recruited during both execution and imagination, increased brain activity was observed in the PMC (both transitive and intransitive gestures) and PPC (for transitive gestures) for execution as opposed to imagination. In fact, hemodynamic responses of PPC reveal its specificity for object-related action. Regression analysis revealed that increasing RP peak amplitudes predicted increasing d values within the SMA, in all conditions. In contrast, RP measures predicted d values within PMC (both transitive and intransitive gestures) and PPC (for transitive gestures) only when the gesture were actually executed. In sum, this study confirms the role of RP in motor planning for both gesture execution and imagination, proving evidence of different recruitment of SMA during gesture planning, in both condition of transitivity. Second, our data prove that shared activations in SMA were observed even during proper gesture execution and imagination. Third, this work indicates that RP – as an electrophysiological cortical marker of motor planning – largely predicts the subsequent brain activity during both gesture execution and imagination. Finally, the present study reveal that partially different networks and processes support distinct tasks (execution vs. imagination) and types of gesture (transitive vs. intransitive), in relation to the different contribution of parietal cortex.