Associative learning allows an individual to acquire an association between a sensory cue and an outcome resulting from a specific response. Associative learning plays a vital role in the ability to learn new associations that allow human beings to optimally respond to the world around them. Research in humans and primates supports an important role for the caudate in associative learning. Our objective was to determine whether caudate stimulation could modulate associative learning in humans and to examine the neural circuitry involved in this process.