Neurons of rat motor cortex become active during both grasping execution and grasping observation

In non-human primates, a subset of frontoparietal neurons (mirror neurons) respond both when an individual executes an action and when it observes another individual performing a similar action.1di Pellegrino G. Fadiga L. Fogassi L. Gallese V. Rizzolatti G. Understanding motor events: a neurophysiological study.Exp. Brain Res. 1992; 91: 176-180Google Scholar, 2Gallese V. Fadiga L. Fogassi L. Rizzolatti G. Action recognition in the premotor cortex.Brain. 1996; 119: 593-609Google Scholar, 3Umiltà M.A. Kohler E. Gallese V. Fogassi L. Fadiga L. Keysers C. Rizzolatti G. I know what you are doing. a neurophysiological study.Neuron. 2001; 31: 155-165Google Scholar, 4Kohler E. Keysers C. Umiltà M.A. Fogassi L. Gallese V. Rizzolatti G. Hearing sounds, understanding actions: action representation in mirror neurons.Science. 2002; 297: 846-848Google Scholar, 5Fogassi L. Ferrari P.F. Gesierich B. Rozzi S. Chersi F. Rizzolatti G. Parietal lobe: from action organization to intention understanding.Science. 2005; 308: 662-667Google Scholar, 6Tkach D. Reimer J. Hatsopoulos N.G. Congruent activity during action and action observation in motor cortex.J. Neurosci. 2007; 27: 13241-13250Google Scholar, 7Dushanova J. Donoghue J. Neurons in primary motor cortex engaged during action observation.Eur. J. Neurosci. 2010; 31: 386-398Google Scholar, 8Kraskov A. Dancause N. Quallo M.M. Shepherd S. Lemon R.N. Corticospinal neurons in macaque ventral premotor cortex with mirror properties: a potential mechanism for action suppression?.Neuron. 2009; 64: 922-930Google Scholar Mirror neurons constitute an observation and execution matching system likely involved in others’ actions processing3Umiltà M.A. Kohler E. Gallese V. Fogassi L. Fadiga L. Keysers C. Rizzolatti G. I know what you are doing. a neurophysiological study.Neuron. 2001; 31: 155-165Google Scholar,5Fogassi L. Ferrari P.F. Gesierich B. Rozzi S. Chersi F. Rizzolatti G. Parietal lobe: from action organization to intention understanding.Science. 2005; 308: 662-667Google Scholar,9Prather J.F. Peters S. Nowicki S. Mooney R. Precise auditory-vocal mirroring in neurons for learned vocal communication.Nature. 2008; 451: 305-310Google Scholar and in a large set of complex cognitive functions.10Bonini L. Ferrari P.F. Evolution of mirror systems: a simple mechanism for complex cognitive functions.Ann. N Y Acad. Sci. 2011; 1225: 166-175Google Scholar,11Mattar A.A. Gribble P.L. Motor learning by observing.Neuron. 2005; 46: 153-160Google Scholar Here, we show that the forelimb motor cortex of rats contains neurons presenting mirror properties analogous to those observed in macaques. We provide this evidence by event-related potentials acquired by microelectrocorticography and intracortical single-neuron activity, recorded from the same cortical region during grasping execution and observation. Mirror responses are highly specific, because grasping-related neurons do not respond to the observation of either grooming actions or graspable food alone. These results demonstrate that mirror neurons are present already in species phylogenetically distant from primates, suggesting for them a fundamental, albeit basic, role not necessarily related to higher cognitive functions. Moreover, because murine models have long been valued for their superior experimental accessibility and rapid life cycle, the present finding opens an avenue to new empirical studies tackling questions such as the innate or acquired origin of sensorimotor representations and the effects of social and environmental deprivation on sensorimotor development and recovery.