Online research in philosophy

Commonsense says we are isolated. After all, our bodies are physically separate. But Seneca’s colamus humanitatem, and John Donne’s observation that “no man is an island” suggests we are neither entirely isolated nor separate. A recent discovery in neuroscience—that of mirror neurons—argues that the brain and the mind is neither built nor functions remote from what happens in other individuals. What are mirror neurons? They are brain cells that process both what happens to or is done by an individual, and, as it were, its perceived “refl ection,” when that same thing happens or is done by another individual. Thus, mirror neurons are both activated when an individual does a particular action, and when that individual perceives that same action done by another. The discovery of mirror neurons suggests we need to radically revise our notions of human nature since they offer a means by which we may not be so separated as we think. Humans unlike other apes are adapted to mirror interact nonverbally when together. Notably, our faces have been evolved to display agile and nimble movements. While this is usually explained as enabling nonverbal communication, a better description would be nonverbal commune based upon mirror neurons. I argue we cherish humanity, colamus humanitatem, because mirror neurons and our adapted mirror interpersonal interface blur the physical boundaries that separate us.

The discovery of mirror neurons has been hailed as one of the most exciting developments in neuroscience in the past few decades. These neurons discharge in response to the observation of others’ actions. But how are we to understand the function of these neurons? In this paper I defend the idea that mirror neurons are best conceived as components of a sensory system that has the function to perceive action. In short, mirror neurons are part of a hitherto unrecognized “sixth sense”. In this spirit, research should move toward developing a psychophysics of mirror neurons.

This commentary points to the lack of sound data supporting Corballis's thesis that there is a general left-hemisphere dominance for nonverbal vocal production in mammals. I also point out that area F5 in the rhesus monkey, which Corballis considers as homologous to Broca's area, contains not only visual “mirror” neurons but also auditory “mirror” neurons. This weakens Corballis's thesis that language developed exclusively at the gestural level.

The notion that manual gestures played an important role in the evolution of human language was strengthened by the discovery of mirror neurons in monkey area F5, the proposed homologue of human Broca's area. This idea is central to the thesis developed by Arbib, and lending further support to a link between motor resonance mechanisms and language/communication development is the case of autism and congenital blindness. We provide an account of how these conditions may relate to the aforementioned theory.

Mirror systems must be supplemented by a planning capability to allow language to evolve. A capability for creating, storing, and executing plans for sequences of actions, having evolved in primates, was applied to sequences of communicatory acts. Language could exploit this already-existing capability. Further steps in language evolution may parallel steps seen in the development of modern children.

Mirror neurons are neurons which fire in two distinct conditions: (i) when an agent performs a specific action, like a precision grasp of an object using fingers, and (ii) when an agent observes that action performed by another. Some theorists have suggested that the existence of such neurons may lend support to the simulation approach to mindreading (e.g. Gallese and Goldman, 1998, 'Mirror neurons and the simulation theory of mind reading'). In this note I critically examine this suggestion, in both its original and a revised form (due to Iacoboni et al., 2005, 'Grasping the intentions of others with one's own mirror neuron system'), and argue that the existence of mirror neurons can in fact tell us very little about how intentional attribution actually proceeds.

Mirror neurons form a poor basis for Arbib's account of language evolution, failing to explain the creativity that must precede imitation, and requiring capacities (improbable in hominids) for categorizing situations and unambiguously miming them. They also commit Arbib to an implausible holophrastic protolanguage. His model is further vitiated by failure to address the origins of symbolization and the real nature of syntax.

The evolutionary continuity between the prespeech functions of premotor cortex and its new linguistic functions, the main thesis of MacNeilage's target article, is confirmed by the recent discovery of “mirror” neurons in monkeys and a corresponding action-observation/action-execution matching system in humans. Physiological data (and other considerations) appear to indicate, however, that brachiomanual gestures played a greater role in language evolution than MacNeilage would like to admit.

We believe that an account of the role of mirror neurons in language evolution should involve a greater emphasis on the auditory properties of these neurons. Mirror neurons in premotor cortex which respond to the visual and auditory consequences of actions allow for a modality-independent and agent-independent coding of actions, which may have been important for the emergence of language.

We focus on the evolution of action capabilities which set the stage for language, rather than analyzing how further brain evolution built on these capabilities to yield a language-ready brain. Our framework is given by the Mirror System Hypothesis, which charts a progression from a monkey-like mirror neuron system (MNS) to a chimpanzee-like mirror system that supports simple imitation and thence to a human-like mirror system that supports complex imitation and language. We present the MNS2 model, a new model of action recognition learning by mirror neurons of the macaque brain and augmented competitive queuing, a model of opportunistic scheduling of action sequences as background for analysis of modeling strategies for simple imitation as seen in the great apes and complex/goal-directed imitation as seen in humans. Implications for the study of language are briefly noted.