Mirror Neurons

Mirror neurons are cells which respond both when an individual performs a particular action, such as picking up a peanut, and when the individual observes another performing the same action. Mirror neurons have been directly observed in macaque ventral premotor cortex and  inferior parietal cortex using in vivo electrophysiology. Mirror responses have also been observed in the homologous human regions using functional neuroimaging and systems-level electrophysiology. Experiments have shown that macaque mirror neurons respond only to manual actions which involve objects, while human mirror regions also respond to intransitive manual actions. Because mirror neurons activate "as if" the observer were actually carrying out another's actions, they are hypothesized to be a neural substrate for mental simulation of  others' behavior. They are hypothesized to play a role in a broad variety of social cognitive abilities including action understanding, empathy, imitation, and language, and appear to be dysfunctional in autism and schizophrenia. Evaluation: Speculative. First, it is possible that observed differences in human and monkey mirror responses are due to differences in methodology. Experiments investigating the human and macaque mirror systems with equivalent methodology are needed to disambiguate this issue. Second, it may be that the macaque mirror system is specialized while the human mirror system retains the ancestral condition, or that the human phenotype is a hominoid specialization rather than a human specialization. Comparisons with other hominoid and anthropoid species  are needed to disambiguate this issue.