1. Howard Hughes Medical Institute, Cambridge, MA 02139, USA.
2. Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.
3. McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
4. Department of Brain and Cognitive Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
5. Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.