Is the mirror cracked?

Abstract

Few recent discoveries in the field of neuroscience have given rise to quite as much interest and controversy as that of mirror neurons, first reported by Giacomo Rizzolatti and his colleagues at the University of Parma in 1992. The first full description of these intriguing entities was published 4 years later in Brain (Gallese et al. , 1996). These authors described the activity of a group of neurons recorded in the ventral premotor cortex of the awake macaque monkey, in a subdivision referred to as F(rontal)5. These F5 neurons fired during particular types of grasp carried out by the monkey; there was nothing surprising about that, since this area had already been identified as a cortical area that was grasp-related. The striking finding was that the same neurons also discharged in a highly reproducible way as the monkey observed a human experimenter making a similar grasp. There was no evidence that this discharge was related to covert movements made by the monkey as it watched: the discharge was clearly evoked by the action of another individual. This fascinating discovery has now been confirmed by several other laboratories (Kilner and Lemon, 2013). Gregory Hickok’s book on this controversial subject carries an intentionally mischievous title: in fact, there is nothing mythological about the existence of mirror neurons (Arbib, 2015), and their discovery has completely changed the way we think about how our own brain interacts with that of others. However, there are plenty of stories about how mirror neurons might function, and in particular how experimental details of mirror neurons acquired in monkeys might illuminate the function of a ‘mirror neuron system’ in humans. Hickok’s well-known difficulties with the proposed functions of a human mirror neuron system stem from two major sets of issues. One is the tension introduced by linking …