by Krishna C Puvvada, Jonathan Z Simon. The preprint was originally posted on bioRxiv on April 10, 2017 (DOI: https://doi.org/10.1101/124750). The authors have responded to this review, and you can find the comments on bioRxiv. The article is now published in The Journal of Neuroscience (DOI: 10.1523/JNEUROSCI.0938-17.2017).