Light from outside the brain can turn on nerve cells in monkey brains

An extra-sensitive molecule made nerve cells respond to dim light

nerve cell illustration

With a new type of light-sensitive protein, blue light activated nerve cells deep within a monkey’s brain. Orange light stopped the extra activity.

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CHICAGO — Light pulses from outside a monkey’s brain can activate nerve cells deep within. This external control, described October 20 at the annual meeting of the Society for Neuroscience, might someday help scientists treat brain diseases such as epilepsy.

Controlling nerve cell behavior with light, a method called optogenetics, often requires thin optical fibers to be implanted in the brain (SN: 1/15/10). That invasion can cause infections, inflammation and tissue damage, says study coauthor Diego Mendoza-Halliday of MIT.

He and his colleagues created a new light-responsive molecule, called SOUL, that detects extra dim light. After injecting SOUL into macaque monkeys’ brains, researchers shined blue light through a hole in the skull. SOUL-containing nerve cells, which were as deep as 5.8 millimeters in the brain, became active. A dose of orange light stopped this activity.

SOUL can’t sense light coming through the macaques’ skulls. But in mice, the system works through the skull, the researchers reported.

LEDs implanted just under people’s skulls might one day be used to treat brain diseases. Such a system might be able to temporarily turn off nerve cells that are about to cause an epileptic seizure, for instance. “This is basically scooping out a piece of brain and then putting it back in a few seconds later,” when the risk of a seizure has dropped, Mendoza-Halliday says.

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