1 Yale School of Medicine, Department of Neurobiology, 333 Cedar Street, New Haven, CT 06510, USA. Electronic address: david.mccormick@yale.edu.
2 Perelman School of Medicine, University of Pennsylvania, Department of Neuroscience, 211 Clinical Research Building, 415 Curie Boulevardoulevard, Philadelphia, PA 19104, USA. Electronic address: nusbaum@mail.med.upenn.edu.