Understanding the effects of task-specific practice in the brain: insights from individual-differences analyses.

We used functional magnetic resonance imaging to study practice effects in different mental imagery tasks. The study was designed to address three general questions: First, are the results of standard group-based analyses the same as those of a regression method in which brain activation changes over individual participants are used to predict task performance changes? With respect to the effects of practice, the answer was clear: Group-based analyses produced different results from regression-based individual-differences analyses. Second, are all brain areas that predict practice effects consistently activated across participants? Again, the answer was clear: Most areas that predicted the effects of practice on performance were not activated consistently over participants. Finally, does practice affect different areas in different ways for different people in different tasks? The answer was again clear: The areas that predicted changes in performance with practice varied for the different tasks, but this was more dramatically and clearly revealed by the individual-differences analyses. In short, individual-differences analyses provided insights into the relation between changes in brain activation and changes in accompanying performance, and these insights were not provided by standard group-based analyses.