Controlling neurons with light

Scientists can now turn on and off specific parts of the brain with a simple flash of light. The new molecular tool, developed by scientists at MIT and Stanford, allows unprecedented control over the brain and could lead to more-effective treatments for epilepsy, Parkinson’s, and other diseases.

These capabilities will also help accelerate the growth in understanding how brains work which relates to the development of artificial intelligence and artificial general intelligence (the hardware for AI is discussed in the preceding article).

New Scientist discusses using light to control neurons

One possibility is that the technology, coupled with a method of getting light into the human skull, could create a Brave New World of neuro-modification in which conditions such as depression or Parkinson’s disease are treated not with sledgehammer drugs or electrodes, but with delicate pinpricks of light. In the long term it is even possible that such treatments could be modified to enhance normal brain function, for example improving memory or alertness.

The technology could also lead to spectacular advances in basic neuroscience, allowing researchers to tease apart the neural circuits that control everything from reflexes to consciousness with unprecedented accuracy. “We’ll be able to understand how specific cell types in the brain give rise to fuzzy concepts like hope and motivation,” predicts Karl Deisseroth, a psychiatrist at Stanford University in California, who is spearheading some of the work.

These new possibilities materialised when neuroscientists finally cracked a long-standing problem in their field: how to take control of individual neurons.

The work is described in this 2007 MIT Technology Review article

Worm workout: A light-activated “off” switch can control the movement of microscopic worms. Scientists engineered the worms to express the switch in motor neurons that control the organisms’ ability to swim. Without light, the worms swim normally. But when they are exposed to yellow light, as indicated by the yellow circle, their motor neurons can no longer function, paralyzing the worms.
Credit: Alexander Gottschalk

Last year, Karl Deisseroth, a bioengineer and physician at Stanford, and Ed Boyden, a bioengineer at MIT, co-opted a light-sensitive channel from jellyfish to create a genetic “on” switch. The channel sits on the cell membrane and opens when exposed to light, allowing positive charge to flow into the cell. Shining light on neurons that are genetically engineered to carry the channel triggers electrical activity within the cell that then spreads to the next neuron in the circuit. (Scientists use optical fibers to shine light into the brain.)

Deisseroth and Boyden have now independently created an “off” switch that works by a similar mechanism. This time the scientists used a gene that codes for a protein pump: when hit with yellow light, it pumps negative charge into the cell, blocking that neuron from firing. Both switches can be used in the same cell, effectively giving neuroscientists a light switch that can be used to turn on and off neural activity.

This newfound ability to precisely control neurons could finally bring answers to major questions about the brain. It might help scientists find the specific cells or neural activity patterns that are involved in cognitive processes, such as attention, or in particular diseases, such as epilepsy.

Scientists can manipulate the specific units of the neural code–the pulses, or spikes, of electrical activity that are transmitted between cells. “We’ve shown we can push spikes around, block them, delay them,” says Boyden. “We can really alter neural coding at a millisecond time scale.” That should allow scientists to determine which aspect of the code–the spikes’ timing or the spikes’ rate–encodes information in the brain, a debate that has raged for decades.