Focused laser beam could help scientists map connections among neurons that underlie behavior.
Researchers at MIT and Paris Descartes University have developed a new optogenetic technique that sculpts light to target individual cells bearing engineered light-sensitive molecules, so that individual neurons can be precisely stimulated.
Until now, it has been challenging to use optogenetics to target single cells with such precise control over both the timing and location of the activation. This new advance paves the way for studies of how individual cells, and connections among those cells, generate specific behaviors such as initiating a movement or learning a new skill.
“Ideally what you would like to do is play the brain like a piano. You would want to control neurons independently, rather than having them all march in lockstep the way traditional optogenetics works, but which normally the brain doesn’t do,” says Ed Boyden, an associate professor of brain and cognitive sciences and biological engineering at MIT, and a member of MIT’s Media Lab and McGovern Institute for Brain Research.
The new technique relies on a new type of light-sensitive protein that can be embedded in neuron cell bodies, combined with holographic light-shaping that can focus light on a single cell.
Boyden and Valentina Emiliani, a research director at France’s National Center for Scientific Research (CNRS) and director of the Neurophotonics Laboratory at Paris Descartes University, are the senior authors of the study, which appears in the Nov. 13 issue of Nature Neuroscience. The lead authors are MIT postdoc Or Shemesh and CNRS postdocs Dimitrii Tanese and Valeria Zampini.
More than 10 years ago, Boyden and his collaborators first pioneered the use of light-sensitive proteins known as microbial opsins to manipulate neuron electrical activity. These opsins can be embedded into the membranes of neurons, and when they are exposed to certain wavelengths of light, they silence or stimulate the cells.
Over the past decade, scientists have used this technique to study how populations of neurons behave during brain tasks such as memory recall or habit formation. Traditionally, many cells are targeted simultaneously because the light shining into the brain strikes a relatively large area. However, as Boyden points out, neurons may have different functions even when they are near each other.
“Two adjacent cells can have completely different neural codes. They can do completely different things, respond to different stimuli, and play different activity patterns during different tasks,” he says.
To achieve independent control of single cells, the researchers combined two new advances: a localized, more powerful opsin and an optimized holographic light-shaping microscope.
For the opsin, the researchers used a protein called CoChR, which the Boyden lab discovered in 2014. They chose this molecule because it generates a very strong electric current in response to light (about 10 times stronger than that produced by channelrhodopsin-2, the first protein used for optogenetics).
They fused CoChR to a small protein that directs the opsin into the cell bodies of neurons and away from axons and dendrites, which extend from the neuron body. This helps to prevent crosstalk between neurons, since light that activates one neuron can also strike axons and dendrites of other neurons that intertwine with the target neuron.
Boyden then worked with Emiliani to combine this approach with a light-stimulation technique that she had previously developed, known as two-photon computer-generated holography (CGH). This can be used to create three-dimensional sculptures of light that envelop a target cell.
Traditional holography is based on reproducing, with light, the shape of a specific object, in the absence of that original object. This is achieved by creating an “interferogram” that contains the information needed to reconstruct an object that was previously illuminated by a reference beam. In computer generated holography, the interferogram is calculated by a computer without the need of any original object. Years ago, Emiliani’s research group demonstrated that combined with two-photon excitation, CGH can be used to refocus laser light to precisely illuminate a cell or a defined group of cells in the brain.
In the new study, by combining this approach with new opsins that cluster in the cell body, the researchers showed they could stimulate individual neurons with not only precise spatial control but also great control over the timing of the stimulation. When they target a specific neuron, it responds consistently every time, with variability that is less than one millisecond, even when the cell is stimulated many times in a row.
“For the first time ever, we can bring the precision of single-cell control toward the natural timescales of neural computation,” Boyden says.
Using this technique, the researchers were able to stimulate single neurons in brain slices and then measure the responses from cells that are connected to that cell. This paves the way for possible diagramming of the connections of the brain, and analyzing how those connections change in real time as the brain performs a task or learns a new skill.
One possible experiment, Boyden says, would be to stimulate neurons connected to each other to try to figure out if one is controlling the others or if they are all receiving input from a far-off controller.
“It’s an open question,” he says. “Is a given function being driven from afar, or is there a local circuit that governs the dynamics and spells out the exact chain of command within a circuit? If you can catch that chain of command in action and then use this technology to prove that that’s actually a causal link of events, that could help you explain how a sensation, or movement, or decision occurs.”
As a step toward that type of study, the researchers now plan to extend this approach into living animals. They are also working on improving their targeting molecules and developing high-current opsins that can silence neuron activity.
The Latest on: Optogenetic molecules
Engineers create most efficient red light-activated optogenetic switch for mammalian cells
on March 13, 2018 at 8:12 am
This is the most efficient so-called 'optogenetic switch' activated by red and far-red light that has been successfully designed and tested in animal cells -- and it doesn't require the addition of sensing molecules from outside the cells. A team of ... […]
Engineers Develop Most Efficient Red-Light-Activated Switch That Can Turn Genes on and off in Mammalian Cells
on March 13, 2018 at 7:31 am
This is the most efficient so-called “optogenetic switch” activated by red and far-red light that has been successfully designed and tested in animal cells—and it doesn’t require the addition of sensing molecules from outside the cells. The light ... […]
Next-generation optogenetic molecules control single neurons
on November 12, 2017 at 4:00 pm
Researchers at MIT and Paris Descartes University have developed a new optogenetic technique that sculpts light to target individual cells bearing engineered light-sensitive molecules, so that individual neurons can be precisely stimulated. "Ideally what ... […]
Neuroscientists Wirelessly Control the Brain of a Scampering Lab Mouse
on November 28, 2016 at 12:00 pm
This optogenetic technology gives researchers a way to “turn ... Then, when a flash of light hits the neuron, the protein opens up ion channels, letting charged molecules flow in. The process replicates the natural change in electrical potential that ... […]
First Human Test of Optogenetics Could Restore Sight to the Blind
on February 19, 2016 at 9:52 am
Testing optogenetic therapy in the eye is an ideal first human trial since the procedure doesn’t require implants or complicated surgery. “All you really have to do is inject some sort of package to deliver these light sensitive molecules into the ... […]
How Optogenetics Could Shine a Light on the Causes and Treatment of OCD
on November 24, 2015 at 5:17 am
"This kind of optogenetic approach ... could help us identify new treatment ... "There's been a big debate in the field," added Satinder Kaur Singh, who studies the molecules involved in disorders like OCD at Yale University. "But what these studies ... […]
The promise of optogenetics in cell biology: interrogating molecular circuits in space and time
on December 19, 2010 at 4:00 pm
Optogenetic modules offer cell biologists unprecedented new ... More than ever, we now appreciate that the cell is not a bag of molecules but an anisotropic structure with highly complex spatial organization. We can see examples of how this organization ... […]
via Google News and Bing News