Exploring the functional and anatomical bases of mirror-image and anatomical imitation: the role of the frontal lobes

Humans are the most imitative species on earth, but how imitation is accomplished and which areas of the brain are directly involved in different kinds of imitation is still under debate. One view is that imitation entails representing observed behaviours as a set of hierarchically organised goals, which subsequently drive the construction of an action pattern [Bekkering, H., Wohlschläger, A., & Gattis, M. (2000). Imitation of gestures in children is goal-directed. The Quarterly Journal of Experimental Psychology, 53, 153-164; Wohlschläger, A., Gattis, M., & Bekkering, H. (2003). Action generation and action perception in imitation: An instance of the ideomotor principle. Philosophical Transactions of the Royal Society of London, 358, 501-515]. On this view, when working memory resources are limited, only the goals at the top-end of the hierarchy will be accurately reproduced. In the present study, neurologically intact participants and patients with frontal and non-frontal lesions were asked to make imitative responses that were either mirror-image (e.g., the observer's right side corresponding to the model's left side) or anatomically (e.g., the observer's right side corresponding to the model's right side) matching. Experiment 1 confirmed that individuals with brain damage, though globally impaired compared with neurologically intact controls, nevertheless followed the same goal hierarchy. However, there was a selective deficit in performing anatomical imitation for the frontal group. Experiment 2 demonstrated that the problem for frontal patients stemmed from an impaired ability to remember and reproduce incompatible stimulus-response mappings, which is fundamental for the selection of the appropriate frame of reference during anatomical imitation.