Using light to control brain cells – neuroscientist Karl Deisseroth explains how he made his Nobel-winning discovery

In the early 1990s, Karl Deisseroth, a future neuroscientist, was training to be a doctor and rotating through psychiatric patient care. During this time, he became increasingly fascinated by the brain's mystery and the challenges in understanding its function. In the late 1990s, as a medical student, Deisseroth's interest in the brain deepened, leading him to pursue a Ph.D. in neuroscience.

Deisseroth's research focused on finding a way to control specific cells in the brain through genetics. He aimed to develop a treatment or intervention targeting particular cells, such as dopamine or serotonin neurons, by inserting specific genes into them. To achieve this, he turned to a gene from a single-celled algae called channelrhodopsin-2, which was identified by Peter Hegemann and Georg Nagel.

This gene, derived from a photosynthetic microbe, proved to be the most effective in activating mammalian neurons when exposed to light.

Deisseroth's breakthrough came when he inserted this algae gene into rat cells in a dish and exposed them to light while comparing them to cells without the gene. He observed that the cells with the algae gene showed activation when exposed to light, while the others did not. This discovery marked a significant milestone for Deisseroth, as it demonstrated the potential of optogenetics – the ability to control specific nerves using light in the brain.

The initial experiments in live animals took almost three years to yield results. However, in 2007, Deisseroth and his team successfully controlled the behavior of a freely moving mouse by inserting a fiber optic into the mouse's motor cortex and activating it with a laser. When the laser was turned on, the mouse began moving in circles, and when it was turned off, the mouse returned to its original state. This experiment validated the potential of optogenetics in understanding and treating neuropsychiatric conditions.