On beyond mirror neurons: internal representations subserving imitation and recognition of skilled object-related actions in humans.

A considerable recent literature argues that the same representations, encoded by inferior prefrontal and parietal cells known as "mirror neurons", may be activated in both production and recognition of object-related actions. Here, we test several predictions derived from the contemporary literature on the parity between production and recognition and the putative emergence of the mirror neuron system from a system coding hand-object interactions. Forty-four patients with left-hemisphere stroke, 21 of whom exhibited ideomotor apraxia, performed a number of pantomime imitation and recognition tasks, and performance was scored with respect to hand posture, arm posture, amplitude, and timing. Consistent with predictions, there were strong relationships between object-related pantomime imitation and object-related pantomime recognition, and between imitation and recognition of the hand posture component of object-related actions. Skilled object-related gesture representations are likely to be closely tied to evolutionarily more primitive systems controlling object grasping, to emerge from a mapping between object and action information coded by ventral and dorsal streams, and to be lateralized to the left hemisphere in humans.