Language within our grasp

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Abstract

In monkeys, the rostral part of ventral premotor cortex (area F5) contains neurons that discharge, both when the monkey grasps or manipulates objects and when it observes the experimenter making similar actions.  These neurons (mirror neurons) appear to represent a system that matches observed events to similar, internally generated actions, and in this way forms a link between the observer and the actor.  Transcranial magnetic stimulation and positron emission tomography (PET) experiments suggest that a mirror system for gesture recognition also exists in humans and includes Broca's area. We propose here that such an observation/execution matching system provides a necessary bridge from `doing' to `communicating', as the link between actor and observer becomes a link between the sender and the receiver of each message.

Section snippets

The mirror system

Neurons located in the rostral part of monkey inferior area 6 (area F5) discharge during active movements of the hand or mouth, or both2, 3, 4. Some years ago we found that in most F5 neurons, the discharge correlates with an action, rather than with the individual movements that form it[3]. Accordingly, we classified F5 neurons into various categories corresponding to the action associated with their discharge. The most common are: `grasping with the hand' neurons, `holding' neurons and

What is area F5?

Although doubts have been expressed[12], most authors share the view that the rostral part of the monkey ventral premotor cortex (area F5) is the monkey homolog of Broca's area in the human brain. The reasons for this view are: that both F5 and Broca's area are parts of inferior area 6 (13, 14, 15) and their location within the agranular frontal cortex is similar (Appendix A); and cytoarchitectonically, there are strong similarities between area 44 (the caudal part of Broca's area) and F5 (14,

The mirror system in humans

The first demonstration of a mirror system in humans was provided by Fadiga et al.[28] The rationale of their experiment was the following: if the observation of an action activates the premotor cortex in humans as it does in monkeys, then magnetic transcranial stimulation should induce, during action observation, an enhancement of motor-evoked potentials recorded from those muscles that are active when the observed action is executed. Their results confirmed the hypothesis: during the

Action recognition and communication

Animals' calls and human speech are undoubtedly different phenomena. Among the many aspects that differentiate them is a marked difference in the anatomical structures underlying the two behaviors. Animals calls are mediated primarily by the cingulate cortex plus some diencephalic and brain stem structures33, 34. Speech is mediated essentially by a circuit whose main nodes are the classical Broca's and Wernicke's areas, both located on the lateral cortical surface.

Our proposal is that the

A pre-linguistic `grammar' of action in the monkey brain

In order to provide abstract expression of the `meanings' of neural activity in premotor cortex (monkey area F5), we have chosen `case grammar' as a representation of sentence structure. Case grammar organizes sentences around action frames with slots for different roles. The key paper for case structure is `The Case for Case' by Fillmore[36], although many of the ideas about case have now been absorbed in the thematic structure of the lexicon that is an integral component of the Chomskian

From action to speech

Returning to our previous query as to which was the initial communicative gestural system in primates, we now distinguish between systems that are closed in the sense that they have a small, fixed repertoire and systems whose elements can be combined to yield an open repertoire of meaning. We argue that: (1) the mimetic capacity inherent to F5 and Broca's area had the potential to produce various types of closed systems related to the different types of motor fields present in that area (hand,

A historical coda

The debate on the origin of language has a long history. Clearly we side with those authors who see a common origin for human speech and some forms of communications in primates, with gestural communication playing an important role in human language genesis52, 53, 54, 55, 56. Chomsky has long argued that language is determined by innate, biologically determined abilities in conjunction with exposure to the language in the environment[57]; to learn a grammar the child must simply use a few

Acknowledgements

We thank Massimo Matelli for his help with the anatomical figure. The work was supported by HFSP and BIOMED 2.

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