It is currently not known whether caffeine has an enhancing effect on long-term memory in humans. In this study, Borota and colleagues examined the effects of caffeine on long-term memory. They found that a specific caffeine dose administered shortly after participants studied images improved image-recognition performance a day later. The full dose-response curve followed an inverted U-shape. The authors suggest that caffeine may enhance consolidation of long-term memories in humans, separately from other cognitive-enhancing effects that it may have.

Borota D, Murray E, Keceli G, Chang A, Watabe JM, Ly M, Toscano JP and Yassa MA: Post-study caffeine administration enhances memory consolidation in humans.  Nature Neuroscience [Epub ahead of print, January 12, 2014; doi:10.1038/nn.3623].

http://www.nature.com/neuro/journal/vaop/ncurrent/abs/nn.3623.html