The mirror neuron system simply. An hypothesis? - biomed 2013

The announcement that mirror neurons (MNs) had been found in macaques was made in 1996. The ensuing MN System theory (MNST) was based on the “nearly simultaneous” activity of some neurons detected both when the macaque observed an investigator's action and when it performed the action (e.g. grasp to eat). Studying the seminal investigations on macaques published in the literature, we realized that poorly defined time-scales could lead to multiple interpretations. We also noticed that in the original experimental protocol the synchronization between the observed event and the neural activity hypothetically related to the event itself was not investigated. In spite of this criticism, the MNST has enjoyed an extraordinary popularity in general media as well as in the scientific community, and monkeys have, almost magically, acquired the functional ability of MNs. In this paper, we analyze some recent studies about the MNST, specifically those about direct measurements on humans by means of implanted electrodes performed by Mukamel and colleagues in 2010. We also consider some experiments performed on monkeys by Rochat et al. in 2010 and some indirect measurements on humans made by Kujala et al. in 2012. We find the conclusions of the authors of these works to be quite simplistic relative to the inherent complexity of neural networks, reinforcing our interpretation against the MNST. We suggest the reported measurements are the result of conventional neural activity related to the events considered (i.e. grasping, both observed and executed) and are not necessarily imputable to the hypothetical MNs.