Localization of electrode positions in the LHb and VTA. Oval symbols indicate the electrode positions, corresponding to the approximate extent of Prussian blue reaction product for each subject (see Fig. 1). Continuous black lines represent subjects that were stimulated during acquisition (sessions 1–5), and dotted black lines represent subjects that were stimulated after acquisition (sessions 6–10). White and light gray lines represent subjects that were anatomical controls stimulated in regions adjacent to the LHb (light gray for hippocampus, white for thalamus) or VTA (white) during acquisition.