"It's turning out to be a very powerful and convenient tool," says MIT professor of electrical engineering Clifton Fonstad, co-lead author of the paper.
Blue for on, yellow for off
Neurons in the brain are not naturally responsive to light, so scientists sensitize these cells with molecules called opsins, light-detecting proteins naturally found in algae and bacteria. Genes for an opsin are transferred to the neurons in a mouse's brain using gene therapy, a process in which DNA is ferried into a cell via a carrier such as a harmless virus. The carrier can be instructed to deliver the DNA package only to certain types of cells.
Different colors of light turn different flavors of opsin on blue might cause one opsin to activate a cell, while yellow might cause another opsin to silence it. Neurons that are sensitized with opsins gain these abilities to respond to light.
The response of an individual neuron whether to turn on or turn off depends on the type of opsin it was sensitized with, and the color of light used to illuminate it. In this way, the tool gives neuroscientists an unprecedented level of control over individual neurons in the brain.
Teams from around the world are currently using the technology developed by Boyden's group to study some of the most profound questions neuroscience tries to answer, such as how memory works, the connections between memory and emotion, and the difference between being awake and being asleep.
"I'm really excited about how the brain computes the ebb and flow of consciousness," Boyden says. "We know so little about the brain."
A better understanding of the brain may lead to another benefit of this technology: therapy. If a particular type of cell malfunctions in a particular disease, scientists ma
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