Mirror Neurons in Monkey Premotor Area F5 Show Tuning for Critical Features of Visual Causality Perception

Humans derive causality judgments reliably from highly abstract stimuli, such as moving discs that bump into each other [1]. This fascinating visual capability emerges gradually during human development [2], perhaps as consequence of sensorimotor experience [3]. Human functional imaging studies suggest an involvement of the "action observation network" in the processing of such stimuli [4, 5]. In addition, theoretical studies suggest a link between the computational mechanisms of action and causality perception [6, 7], consistent with the fact that both functions require an analysis of sequences of spatiotemporal relationships between interacting stimulus elements. Single-cell correlates of the perception of causality are completely unknown. In order to find such neural correlates, we investigated the responses of "mirror neurons" in macaque premotor area F5 [8, 9]. These neurons respond during the observation as well as during the execution of actions and show interesting invariances, e.g., with respect to the stimulus view [10], occlusions [11], or whether an action is really executed or suppressed [12]. We investigated the spatiotemporal properties of the visual responses of mirror neurons to naturalistic hand action stimuli and to abstract stimuli, which specified the same causal relationships. We found a high degree of generalization between these two stimulus classes. In addition, many features that strongly reduced the similarity of the response patterns coincided with the ones that also destroy the perception of causality in humans. This implies an overlap of neural structures involved in the processing of actions and the visual perception of causality at the single-cell level.