Intersubject synchrony of viewers during naturalistic observational self-learning of a complex bimanual task.

Watching an instructional video has become a common way to learn a new task. However, we have but a sparse understanding of the neural processes involved during observational learning in naturalistic settings. Recently developed data driven methods for analyzing brain activity provide an opportunity for further investigation. Here, we evaluate intersubject synchrony during fMRI to understand common brain processes during naturalistic observational learning. Participants solitarily watched an instructional video and learned how to fold a paper figure. Three learning runs were sufficient to successfully solve the task. To assess interbrain synchrony, we extended previous principal component (PCA)-based methods to an intersubject principal component analysis (PCA), which offers multiple measures for additional insights into the nature of the synchrony. Using the different metrics of this method, we show a robust synchronous involvement of the action observation execution network (AOEN) in observational learning, between subjects as well as within subjects, regardless of the task or video content. Importantly, additional areas such as the cerebellum, primary motor cortex, control, and sensory integration areas also showed robust synchrony in observational learning. Complimentary to this robust general synchrony, individual regions of the AOEN exhibited task-related differences. Synchrony decreased during the learning process, likely reflecting task state and individual learning strategies. To test the stimulus as a possible source of synchrony, we quantified the temporal structure as the optic flow of the instructional video. Optic flow was strongly related to common activation of the somatomotor areas of the AOEN well beyond visual areas, but could not completely explain synchrony. Thus, although visual motion provides a proxy for meaningful hand actions, our results suggest that intersubject synchrony reflects common cognitive processing during observational learning beyond sensory input.