[Editors] MIT: Pulsing light silences overactive neurons

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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MIT: Pulsing light silences overactive neurons
--Work could lead to non-surgical treatment for epilepsy, Parkinson's
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For Immediate Release
TUESDAY, MAR. 27, 2007
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

PHOTO AVAILABLE

CAMBRIDGE, Mass.--Scientists at the MIT Media Lab have invented a way 
to reversibly silence brain cells using pulses of yellow light, 
offering the prospect of controlling the haywire neuron activity that 
occurs in diseases such as epilepsy and Parkinson's disease.

Such diseases often must be treated by removing neurons that fire 
incorrectly. The new MIT research could lead to the development of 
optical brain prosthetics to control neurons, eliminating the need 
for irreversible surgery.

"In the future, controlling the activity patterns of neurons may 
enable very specific treatments for neurological and psychiatric 
diseases, with few or no side effects," said Edward Boyden, assistant 
professor in the Program in Media Arts and Sciences and leader of the 
Media Lab's new Neuroengineering and Neuromedia Group.

Boyden and Media Lab research affiliate Xue Han published their 
results in the March 21 issue of the online journal Public Library of 
Science ONE (PLOS One).

The work takes advantage of a gene called halorhodopsin found in a 
bacterium that grows in extremely salty water, such as the Great Salt 
Lake in Utah. In the bacterium, Natronomas pharaonis, the gene codes 
for a protein that serves as a light-activated chloride pump, which 
helps the bacterium make energy.

When neurons are engineered to express the halorhodopsin gene, the 
researchers can inhibit their activity by shining yellow light on 
them. Light activates the chloride pumps, which drive chloride ions 
into the neurons, lowering their voltage and silencing their firing.

That inhibitory effect may be extremely useful in dealing with 
diseases caused by out-of-control neuron firing, said Boyden. "In 
such diseases, inhibition is more direct than excitation, because you 
can shut down neural circuits that are behaving erratically," he said.

Many epilepsy patients have implanted electrodes that periodically 
give their brains an electric jolt, acting as a defibrillator to shut 
down overactive neurons. This new research opens up the possibility 
of an optical implant that could do the same thing, using light 
instead of electricity. The Media Lab neuroengineering group plans to 
start studying such devices in transgenic mice this year.

The group also plans to use the new method to study neural circuits. 
Last year, Boyden devised a technique to stimulate neurons by shining 
blue light on them, so with blue and yellow light the researchers can 
now exert exquisite control over the stimulation and inhibition of 
individual neurons.

Learning more about the neural circuits involved in epilepsy could 
help scientists develop devices that can predict when a seizure is 
about to occur, allowing treatment (either shock or light) to be 
administered only when necessary, Boyden said.

The technique also offers a way to study other brain diseases, as 
well as normal brain circuitry, offering insight into which brain 
regions and neurons contribute to specific behaviors or pathological 
states, Boyden said.

The halorhodopsin gene was originally discovered in the 1980s, but 
Boyden didn't think its full potential had been explored. The protein 
expressed by the gene turned out to have exactly the right 
characteristics to make it useful in neuron inhibition.

"Often if you are patient and think carefully about what you want to 
do, you can find a molecule that is very close to what you want, and 
with a little bit of luck it will turn out to work," Boyden said.

The halorhodopsin work is one of the first projects from the Media 
Lab Neuroengineering and Neuromedia Group, which was formed about six 
months ago to enhance the Media Lab's study of the brain-body 
relationship.

"The Media Lab has always been interested in studying the interface 
between people and the world," Boyden said, "but now people are 
getting interested in the interface between bodies and brains in the 
world."

The research was funded by an anonymous donor, the MIT Media Lab and 
the Helen Hay Whitney Foundation.

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Written by Anne Trafton, MIT News Office