Precursors to language: Sensory-motor integration, the mirror neuron system, and laterality

This dissertation attempts to understand the link between the mirror neuron system and language by exploring laterality within the mirror neuron system. By considering each hemisphere's representation and specialization for body schema, motor imagery, action observation, and imitation, this research provides new avenues for understanding how a system of action representation may have paved the way for a system for language. The general framework of this research involves integrating behavioral, neuropsychological, and brain imaging techniques with the aim of providing converging evidence about laterality issues in the mirror neuron system.; Using behavioral paradigms, functional magnetic resonance imaging (MM), and transcranial magnetic stimulation (TMS), we tested the sensitivity of each brain hemisphere to actions via the visuo-motor channels. In these studies, subjects participated in action observation, in kinesthetic imagery, in responding to body stimuli, or in imitation. Each of these methods indicated that both the left and right hemispheres are sensitive to the visuo-motor channels for actions, thus indicating no hemispheric specialization for actions in the visuo-motor channels.; Next we tested lateralization of actions in the auditory modality, which is a strong component of human speech. Specifically, we explored each hemisphere's sensitivity to action sounds. The experimental parameters were similar to those of our TMS action observation study, except with auditory stimuli rather than visual stimuli. We found that only the left hemisphere was sensitive to hand action sounds. This indicates that the left hemisphere mirror system alone may be sensitive to the auditory modality for actions.; Taken together, our results indicate that the mirror system may have functions in each hemisphere. In the right hemisphere, the mirror system seems to be responsive only to visual and motor components of actions. In the left hemisphere, however, actions seem to be coded through multiple modalities coding in this hemisphere seems to contain all the contents of an action. the system particularly suitable for evolving language.