Execution, observation and mental simulation of upper limb gesture for transitive and intransitive action: a fNIRS study

Background: Since decades, human functional neuroimaging studies have investigated the functional equivalence between execution, observation and mental simulation of upper limb movements such as grasping, reaching and performing meaningful actions. Although these tasks have showed recognizably differential areas of activation (e.g. M1 and S1 for execution, STS for observation), numerous fMRI studies have reported widespread overlapping activations over a fronto-parietal network, known as action observation network and including mirror neurons. Nevertheless, the focus of the majority of these studies was on the representation of transitive object-related actions, while the analysis of intransitive ones provoked relatively less attention. Aims: The aim of the present study is to investigate patterns of cerebral hemodynamic activity during execution, observation and mental simulation of transitive gesture (object use, e.g. manipulating a brush) and intransitive gesture (only with communicative content, e.g. waving goodbye). Method: Healthy subject (N = 18) were asked either to execute, observe or mentally simulate transitive and intransitive right upper limb gestures. During the three conditions, NIRS event-related signals were recorded over the frontal, parietal and temporal cortex using eight infrared optode emitters and eight optode detectors. Results: Preliminary data analysis conducted on oxy-hemoglobin changes revealed similar activations within motor tasks (M1) but also differential patterns of hemodynamic activity (parietal areas). Moreover, transitive versus intransitive gestures showed different hemodynamic modulation, with increased M1 activity for transitive gestures. Conclusions: These results were discussed taking into consideration the role of semantic information in gesture representation.