NEUROPHOTONICS FEATURE


basic science research… but scientists have great hopes that knowledge acquired using model systems could eventually be applied in humans to treat various diseases affecting the brain,’ said Méthot. Marie Carlen, associate professor of


Neuroscience at the Karolinska Institute at the University in Solna, Sweden, is one research who is studying living animals using optogenetics techniques. Laser and fibre optics are used to


‘insert’ varying intensities of light to be directly into specific areas in the brains of experimental animals, which causes specific neurons to be turned on and off. The corresponding changes observed


in the animals’ behaviour give clues as to which cells and regions of the brain are involved in different emotional and physical responses, such as those associated with hunger, fear, anxiety, learning, motivation and more. This element of control happens because of opsins, the molecules in neurons that can be activated by light. Some types of opsins fire off positively charged ions in response to light, making it possible to activate or switch on neurons. Other opsins, by contrast,


“Scientists have great hopes that knowledge acquired using model systems could eventually be applied in humans to treat various diseases affecting the brain”


send out negatively charged ions when in contact with light, and inhibit or turn off neurons. Genetic engineering has allowed opsins to be tailor-made to fulfill specific functions and better meet the needs of researchers seeking clues as to which neuronal functions correlate with behaviours. It is already the case that light can be used to manipulate opsins with a high degree of precision allowing for neurons in specific locations to be turned on and off for specific lengths of times. The lasers and optics needed for


optogenetic experiments are specialised. Marie Carlen works with Swedish photonics firm Cobolt to develop the laser devices that best enable her team to advance their studies of the cognitive functions of animals. Calibrating laser tools so that they deliver sufficient light to the area of an animal brain to switch specific neurons on and off without damaging the tissue is a complex task, involving the correlation and adjustment


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of many different factors such as wavelength, power output and stability. In addition, the laser devices have to be flexible enough to move as the animals move. Cobolt offers a variety of user- friendly lasers to meet the various needs of researchers such as Marie Carlen. In other research, Benjamin


Judkewitz, professor in Bioimaging and Neurophotonics at the NeuroCure Cluster in Berlin, is developing a technique to track and image neurons as they interact with each other and communicate inside their natural networks, potentially allowing scientists to model brain activity in real time, as subjects perceive multiple real world phenomena simultaneously and respond. This technique would help scientists, for example, track the emergence and growth of a tumor in a particular location and develop therapies. Immunologists, on the other hand, may be able to study the process by which lymph nodes become swollen – and not just cells in a petri dish. The sheer complexity of the brain and


nervous system, however, makes the task of modelling them a long term project. The brain alone has about 86 billion neurons. Tracking them as they interact with each other to generate complex and ever changing patterns of movement as they respond to their environment is a staggering challenge. To go back to the metaphor of the traffic


system, Judkewitz and his team seek to monitor and model the trajectory not just of one vehicle moving inside a city, but the movement of all vehicles, airplanes and pedestrians in all the cities and transport systems across world at same time and all in real time multiplied by a factor of a billions and all this, on a molecular scale. The limitations of optical microscopy


make the challenge even more difficult. When light is scattered and defracted, it results in the destruction of the information that light photons have been carrying. Judkewitz is developing an optical time reversal technique to counteract the effect of light scattering and to harvest more information from photons. His approach involves using a microscope to send photons back along the path they have travelled, back in space and time, to reproduce what exactly it was that a photon encountered and saw when it was inside tissue. With so many breakthroughs on so


many fronts, there is every reason to be excited about the possibilities of the huge and ever expanding field of neurophotonics. Not only can it help answer fundamental questions of science such as those concerning the nature of consciousness, commented Professor Nägerl, but also be used to solve real-world problems, for example, cures for degenerative diseases such as Alzheimers. EO


Image showing a neuron (green) and synapses (red) December 2017/January 2018 Electro Optics 43


Dr Paul De Koninck


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