Mirror neurons and the lateralization of human language.

Editor's Note: These short reviews of a recent paper in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to mimic the journal clubs that exist in your own departments or institutions. For more information on the format and purpose of the Journal Club, please see Review of Aziz-Zadeh et al. In the premotor cortex of the macaque there are neurons whose firing rates increase when the monkey makes goal directed movements and when the monkey observes similar movements being made by others. These cells are named " mirror neurons. " It has been suggested that by mapping observation of movements onto cells involved in the production of similar movements, mirror neurons help individuals understand and imitate motor goals (Gallese et al., 1996). Several studies have used functional imaging techniques to determine whether mirror neurons exist in humans. Neural activation in response to both movement production and observation has been described in Brodmann area 44 (BA44), located in the pars opercularis of the inferior frontal gyrus (Iacoboni et al., 2005). In the left hemisphere, BA44 contains Broca's area, a brain region that has been the focus of intense study because of its role in language processing and speech production. The close anatomical proximity of mirror neurons to Broca's area has led some to speculate that mirror neurons may have played a role in the lateralization of human language. If true, the human mirror neuron system might also be left lateralized. In their Journal of Neuroscience article, Aziz-Zadeh et al. (2006) used functional magnetic resonance imaging to determine the extent to which the human mirror neuron system is lateralized. Blood oxygen level-dependent (BOLD) neural activity was recorded in each of four experimental conditions. In each condition, subjects saw movies of left and right hands (each hand was presented independently) with the index finger extended between two targets. In the static observation condition , subjects observed a stationary hand. In the action observation condition , subjects watched as the index finger moved toward one of the targets. In the execution condition, the observed hand was stationary, but the subjects moved their own index finger when instructed by an abstract cue. In the imitation condition , the observed index finger moved toward one of the targets and subjects did the same [Aziz-Zadeh et al., 2006, their Fig. made with the same hand as was observed. Images of left hands were …