Sunday, 8 November 2009
Brains powered by light
In the 1990s Peter Hegemann, a German biologist, discovered that green algae commonly found in ponds respond to light by wagging their tail, an interesting phenomenon given that they do not have eyes. When light photons hit the protein coils packed in the algae's cell membrane, a chemical reaction created a tiny gap, causing an ionic current to be produced and the algae's tail to wag. The protein that allowed this reaction is channelrhodopsin-2.
Some years later, American researchers started to wonder whether a similar mechanism could be used to control brain cells if certain neurons were made to behave somewhat like algae. By genetic engineering these scientists were able to do just this: not to make brain cells move but, using channelrhodopsin, to turn them on or off simply with light. The field of optogenetics was born.
What is so beautiful about this technique is that, by harnessing the cunning of viruses, it is possible to make the channelrhodopsin-encoding gene only be expressed in particular targeted neurons. And so far the results have been startling. Flies have been made to jump, mice made to walk in a certain direction, and both to remember events that never happened, all through the power of light. Optogenetics could therefore open the door to precise therapeutics in diseases such as Parkinson's disease and schizophrenia where presently only drugs or surgery can help, neural sledgehammers compared to the surgical scalpel enabled by light-controlled tools.
If its promise holds up, a bulb over someone’s head may someday be seen in a completely new light.