Tim Hines brought this article from MIT News covering activity-induced double-stranded breaks in neurons to our attention:
http://newsoffice.mit.edu/2015/dna-breakage-learning-age-related-damage-0604
And here's the abstract in Cell of the reference paper:
http://www.cell.com/cell/abstract/S0092-8674%2815%2900622-4
Additionally, Mike Wyatt followed up on this as well:
"Post script to the May presentation about modified cytosines. This paper offers pretty good evidence that 5-formyl cytosine is a distinct epigenetic signature, not merely an intermediate going from 5-mC or 5-hmC back to unmodified cytosine."
http://cen.acs.org/articles/93/web/2015/06/Modified-DNA-Base-5-Formylcytosine.html
http://www.nature.com/nchembio/journal/vaop/ncurrent/full/nchembio.1848.html