Yale researchers used light to probe the actions of the neurotransmitter GABA on single synapses along the branches of a neuron.
This photo shows a mouse cortical neuron in red, with dendritic branches that are studded with synaptic spines. Surrounding the neuron are inhibitory axons or fibers (in blue) that are genetically engineered to release GABA when activated by light, a technique known as optogenetics. Learn more →
The Dark Knight Trilogy
Physicist’s tool has potential for brain mapping
A new tool being developed by UT Arlington assistant professor of physics could help scientists map and track the interactions between neurons inside different areas of the brain.
The journal Optics Letters recently published a paper by Samarendra Mohanty on the development of a fiber-optic, two-photon, optogenetic stimulator and its use on human cells in a laboratory. The tiny tool builds on Mohanty’s previous discovery that near-infrared light can be used to stimulate a light-sensitive protein introduced into living cells and neurons in the brain. This new method could show how different parts of the brain react when a linked area is stimulated.
The technology would be useful in the BRAIN mapping initiative recently championed by President Barack Obama, Mohanty said. BRAIN stands for Brain Research Through Advancing Innovative Neurotechnologies and will include $100 million in government investments in research.
“Scientists have spent a lot of time looking at the physical connections between different regions of the brain. But that information is not sufficient unless we examine how those connections function,” Mohanty said. “That’s where two-photon optogenetics comes into play. This is a tool not only to control the neuronal activity but to understand how the brain works.”
The two-photon optogenetic stimulation described in the Optics Letter paper involves introducing the gene for ChR2, a protein that responds to light, into a sample of excitable cells. A fiber-optic infrared beam of light can then be used to precisely excite the neurons in a tissue circuit.
In the brain, researchers would then observe responses in the excited area as well as other parts of the neural circuit. In living subjects, scientists would also observe the behavioral outcome, Mohanty said.
Optogenetic stimulation avoids damage to living tissue by using light to stimulate neurons instead of electric pulses used in past research. Mohanty’s method of using low-energy near-infrared light also enables more precision and a deeper focus than the blue or green light beams often used in optogenetic stimulation, the paper said.
Using fiber optics to deliver the two-photon optogenetic beam is another advance. Previous methods required bulky microscopes or complex scanning beams. Mohanty’s group is collaborating with UT Arlington Department of Psychology assistant professor Linda Perrotti to apply this technology in living animals.
“Dr. Mohanty’s innovations continue to be recognized because of the great potential they hold,” said Pamela Jansma, dean of the UT Arlington College of Science. “Hopefully, his work will one day provide researchers in other fields the tools they need to examine how the human body works and why normal processes sometimes fail.”
He considered the facts and took a deep breath. “Bleed. It’s the term for what alternate timelines do when you spend too much time in one with your alternate self. You start to become aware of things they know, things they did. It’s an attempt for the mind to resolve the paradox.”
“I am the Master.”
Her smile faltered when he introduced himself. She frowned and took a step forward, her head tilted to one side as she regarded him in the new context. “Does that mean you know who I am, then?” Harleen’s eyes widened slightly. “Is that why you apologized?”