Praxic and executive components in tool use learning: the role of imitation

Objectives: The current study intended to investigate whether social learning processes other than imitation can be traced in human adults, particularly in brain-injured patients who have lost their ability to imitate. This was undertaken by exploring the extent to which the observation of how to solve a tool-use task primed the performance of left (LBD) and right (RBD) brain-damaged patients, as well as of healthy adults. Methods: Participants were assigned to a no model condition (N), in which they were left alone to solve the problems, and a demonstration condition (D), in which they could either observe a Correct (C) or an Incorrect + Correct Demonstration (I+C) in which they witness a failed attempt followed by the correct solution of the task. Results: Consistent with predictions, LBD overall performance was significantly worse than that of control subjects, while RBD did not differ from controls. However, there was only a trend in LBD to perform worse than RBD and controls after both type of demonstrations, and alternative non-imitative processes were rarely adopted by both patient groups. Yet, looking at single cases, all LBD scoring below controls in C engaged in (goal) emulation, and all had ideomotor apraxia, those in I+C showed mimicry, and were affected by frontal dysfunction. Conclusions: The left hemisphere is indeed critical for motor control and selective neuropsychological deficits can compromise action imitation and selection of goal-directed movements, independently from each other. Our findings also suggest that when the ability to imitate actions is lost or lowered emulation may come available.