Optical Brain Control: Analyzing and Engineering Normal and Pathological Neural Circuit Dynamics
Neurological disorders affect approximately 1.5 billion people worldwide and cost over $1 trillion per year. For many disorders, few effective treatments exist. Researchers led by Ed Boyden, PhD, are seeking to develop new ways to control specific neural circuits, and they hope that their techniques will eventually help doctors treat problems such as epilepsy and chronic pain.
The brain is composed of many interconnected circuits and many different cell types. Existing technologies for the modulation of neurons are dependent on electrical or magnetic fields, and these techniques are limited because they affect all cells in a given volume and cannot be used to target specific cell types. Boyden’s group hopes to use light to selectively control the behavior of specific types of neurons in the brain.
Their method depends on light-sensitive microbial channel and pump proteins. The channel protein channelrhodopsin-2 is sensitive to blue light, and when activated in the plasma membrane of a neuron, it triggers an action potential. The pump protein halorhodopsin is sensitive to yellow light, and when activated in the plasma membrane of a neuron, it silences the neuron. Thus, channelrhodopsin-2 and halorhodopsin can be used in combination to control neuronal activity.
For these two proteins to be effective, they must be introduced into neurons and exposed to light. Boyden’s group has been able to introduce the proteins into cells using viruses such as lentiviruses and adenoviruses. The researchers are now investigating ways to shine light into the brain using implantable, miniaturized arrays of light-emitting diodes (LED’s) and/or optical fibers.
Boyden’s team has shown that their technique does not cause neurons to become hypersynchronized and that the membrane proteins involved do not provoke an immune response. In the future, Boyden and his fellow researchers hope that their technique will provide a new treatment for neurological disorders and will enhance the effectiveness of certain neural prostheses.
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