In a previous behavioral study (Waechter et al SFN, 2003), using the serial reaction time task, we have demonstrated a facilitation of implicit learning of motor sequences by monetary reward that was independent of motivation; by contrast monetary penalties did not affect learning. These findings were in accord with predictions from neural recordings in the mid-brain dopaminergic system as well as reinforcement learning theories. The learning theories, such as the actor-critic model, further predict that reward will enhance motor learning through the release of dopamine in the striatum thus strengthening cortico-striatal connections. We tested this hypothesis using fMRI in human subjects during the performance of the same behavioral task. As expected, we found significant activation in the putamen during implicit learning in a group of 38 subjects who did not acquire explicit knowledge. Further analysis showed that this sub-area within the putamen also showed a significant effect of reward, but was not act...