There was an error in the acknowledgements section. The correct acknowledgements are as follows: "We thank the Allen Institute for Brain Science for making their data publicly available to the scientific community and for providing us with insights on the data and answers to all of our questions. We specifically would like to thank Chinh Dang, Terri Gillbert, Michael Hawrylycz, John Hohmann, Chris Lau and Joshua Royall for their help and comments. We also thank Ossnat Bar-Shira, Leon French, Lior Kirsch, Uri Shalit and Hadas Taubman for many valuable discussions."