Mirror neurons: a bilaterian innovation?: A new look on mechanisms, function and evolution of the mirror neuron system

Abstract

Mirror neurons are considered to play important roles in human social behaviour. Here I theorise, that the social functions of “mirror neurons” are based upon adaptations in the way in which neurons communicate, rather than upon a newly evolved specific type of neural architecture. Vasopressin and oxytocin are specifically implicated in the modulation of neural communication. The role of these hormones in mirror neuron social function involves the generation of sensory neuron calcium waves. These calcium waves are an important element of a perception-action model-like mechanism. In such a model, perception of patterns imposed by external stimuli are matched to patterns of neural representations of an animal's own physical dimensions and motorcapabilities. By way of this mechanism of oscillatory matching, perception of a conspecific can generate stimulating feedback, which can include the matching of affective states. This principle of directing movement towards a proxy of external stimuli as presented by mechanosensory neurongenerated calcium waves is based on simple mechanisms for chemotaxis: movement along a chemical gradient, towards or away from the source. A basic level of mirror neuron guided interaction with conspecifics is ubiquitous in bilateria, with mirror neurons facilitating close bodyto- body contact and movement-synchronisation. Mirror neurons develop through the basic principles of bilaterian central nervous system organisation with its ability to form map-like neural representations. These map-like neural representation of bilaterian animals' own physical qualities and dimensions are very useful for guiding internal fertilisation. In the developmentally plastic bilaterian central nervous system, which forms relatively complex neural representations of the animals own physical parameters, the dimensions and characteristics of these physical parameters -and thus their neural representationsdepend strongly on the animal's environment. The mirror neuron related abilities to utilise those representations for species recognition and interaction, contributed strongly to an evolutionary feedback process known as sensory drive, that is, the adaptation of communication systems to environmental circumstances. This suggests that mirror neurons were an important driver of the relatively rapid radiation and diversification of bilaterally symmetric animals that occurred during the Cambrian explosion -between 542 and 525 million years ago.