To what extent do human-robot interactions (HRI) rely on social processes similar to human-human interactions (HHI)? To address this question objectively, we use a unique corpus. Brain activity and behaviors were recorded synchronously while participants were discussing with a human (confederate of the experimenter) or a robotic device (controlled by the confederate). Here, we focus on two main regions of interest (ROIs), that form the core of "the social brain", the right temporoparietal junction [rTPJ] and right medial prefrontal cortex [rMPFC]. An new analysis approach derived from multivariate time-series forecasting is used. A prediction score describes the ability to predict brain activity for each ROI, and results identify which behavioral features, built from raw recordings of the conversations, are used for this prediction. Results identify some dierences between HHI and HRI in the behavioral features predicting activity in these ROIs of the social brain, that could explain signicant dierences in the level of activity.