A major problem neuroscience researchers have is controlling one type of cell in the brain without effecting the function of others. Both electrodes, which stimulate the entire area in which they are inserted, and drugs, which act slower than the natural speed of the brain, are not specific enough to stimulate one particular cell type at a time. The brain is made up of thousands of kinds of cells: they come in different shapes, are made up of different molecules, and they connect to different brain regions. In order to learn about the different types of cells in the brain it would be ideal to be able to turn them on or off while leaving others unaltered and see what functions the cells contribute to. Turing cells on and off would be helpful in understanding certain neurological disorders. Drugs which have been developed for disorders such as Alzheimer’s and schizophrenia are able to treat some of the symptoms associated with them but have yet to cure anyone. These drugs also have side effects because they are not specific enough. The same is true with electrical stimulation – the electricity spreads throughout the brain affecting normal circuits in addition to the malfunctioning circuits. What is an alternative solution to drugs or electrodes? Light.
Researchers took protein molecules called channelrhodopsins that could convert light into electricity and inserted them into neurons. Because channelrhodopsins are proteins found in a type of algae that swims towards light, their DNA is encoded in the organism. Once the DNA is inside the neuron, the neuron’s protein-making mechanisms make light-sensitive proteins throughout the cell. The end product is a neuron which can be activated with light (see video). The genetics involved in this process, called optogenetics, allows one cell type to be activated at a time. This technology can be used in many ways including looking at what signals mediate reward and learning, underlying mechanisms for PTSD, and ways to turn circuits in the brain off. A very promising use of optogenetics is with the treatment of epilepsy. In patients where drugs are not effective in stopping seizures, light could be shined on the light-sensitive cells to turn them off. The same technology has been used in other parts of the body besides the brain, such as in the heart cells of mice, and in skin cells. The applications of optogenetics are endless.