Chlamydomonas is a green alga made of a single cell, and it swims toward light. It senses light with an eyespot, a tiny orange dot on its surface. In the early 1990s Peter Hegemann, then at the Max Planck Institute for Biochemistry near Munich, measured the electrical signal the eyespot makes. It came half a millisecond after the light. In the human eye the same job runs through a chain of chemical steps that takes at least 10 milliseconds, so the alga was more than twenty times faster.
Hegemann guessed that a single protein both catches the light and opens a channel for charged particles. Other researchers doubted it, because no known ion channel reacted to light on its own. Around 2000, Japanese researchers published thousands of Chlamydomonas genes, and Hegemann's group spotted two that looked like light-catching proteins. Georg Nagel, at the Max Planck Institute for Biophysics in Frankfurt, put the genes into frog eggs. The eggs made the proteins, and a flash of light opened a channel through them within 0.2 milliseconds. The pair named the proteins channelrhodopsin-1 and channelrhodopsin-2 and published in 2003.
Karl Deisseroth at Stanford wrote to Nagel asking for the DNA. His group put it into rat nerve cells growing in a dish, and in 2005 they showed that blue light set off a nerve signal. The method was named optogenetics in 2006. In 2007 his group made mouse whiskers move by shining light through a thin optical fiber into the part of the brain that controls movement, and with other researchers woke sleeping mice by lighting up one type of nerve cell.
Since then, labs have used light to find the nerve cell circuits behind pain, thirst, eating, attention and memory. An adult human brain has around 90 billion nerve cells, so switching on one kind at a time is a big step. Clinical trials are now testing a channelrhodopsin-like protein in the eyes of people blinded by retinitis pigmentosa. One person given it was able to make out and grasp objects on a table using special light-emitting glasses.
The three laureates share 12 million Swedish kronor.
