Finding the Spark.

It began, as with many good things, at a happy hour. Adam Cohen, a young assistant professor asked whether rhodopsins could be used to optically sense voltage. In the heady days of 2009, channel rhodopsin had just been unveiled as a voltage actuator in neurons. Adam had the insight to question whether rhodopsins could be run in reverse; could optical changes in a protein relay the cellular voltage state using light? This was one of the earliest lessons I learned under his mentorship, and the first piece of advice in this retrospective-turning a scientific question or statement on its head can be the basis for many fantastic research projects.