http://learnmem.cshlp.org/content/15/4/222.full.pdf+html (Publisher version)
Eschenko, O., Ramadan, W., Mölle, W., Born, J., & Sara, S. (2008). Sustained increase in hippocampal sharp-wave ripple activity during slow-wave sleep after learning. Learning & memory, 15(4), 222-228. doi:10.1101/lm.726008.