Sensorimotor training alters action understanding.

The discovery of 'mirror' neurons stimulated intense interest in the role of motor processes in social interaction. A popular assumption is that observation-related motor activation, exemplified by mirror neurons' matching properties, evolved to subserve the 'understanding' of others' actions. Alternatively, such motor activation may result from sensorimotor learning. Sensorimotor training alters observation-related motor activation, but studies demonstrating training-dependent changes in motor activation have not addressed the functional role of such activation. We therefore tested whether sensorimotor learning alters action understanding. Participants completed an action understanding task, judging the weight of boxes lifted by another person, before and after 'counter-mirror' sensorimotor training. During this training they lifted heavy boxes while observing light boxes being lifted, and vice-versa. Compared to a control group, this training significantly reduced participants' action understanding ability. Performance on a duration judgement task was unaffected by training. These data suggest the ability to understand others' actions results from sensorimotor learning.