1. Department of Medicine, Northwestern University, Feinberg School of Medicine, Chicago, IL 60611, USA.
2. Department of Neurobiology and Physiology, Northwestern University, Evanston, IL 60208–3520, USA.
3. Weinberg College of Arts and Sciences, Northwestern University, Evanston, IL 60208–3520, USA.
4. Center for Sleep and Circadian Biology, Northwestern University, Evanston, IL 60208–3520, USA.
5. Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390–9111, USA.
6. Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390–9111, USA.