Optogenetics in Primates: Progress and Opportunities for System Neuroscience and Neuroprosthetics

Optogenetics is a versatile technology which is based on light sensitive membrane proteins. Those membrane proteins are called opsins. They are derived from microbial organisms which use them to orient themselves towards or away from light of specific wavelengths. Surprisingly, opsins can be safely integrated into the membranes of neurons by using viral vectors or transgenetic techniques, thus making the neurons light-sensitive without causing any aversive reaction. When shining light pulses of different wavelengths on the opsin-expressing neurons, we can either elicit or inhibit an action potential depending on the introduced opsin. Channelrhodopsin-2, for example, is an excitatory opsin which causes neurons to spike under the influence of blue light while Halorhodopsin silences neurons during the presence of yellow light. Although just six years have passed since the term optogenetics was coined, the technique quickly became one of the favorite toys of system neuroscientists. It is already used worldwide in flies, fish and rodents. Now, monkeys bring new requirements to the table. Monkeys are extremely valuable animals and are typically trained for months or years. Hence, the number of experiments with each animal is limited and each experiment has to be well planned and be conducted with exceptional care.  The efforts are well justified. Monkeys resemble humans in their cognitive abilities and fine motor skills more than any other standard animal model. They can learn categories, rules and associations, come to decisions, and grasp and manipulate objects in a very human like manner. The neural correlates of these abilities are encoded in areas that are similar to human brain areas. These similarities make monkeys essential for the translation of knowledge, techniques and cures from simpler animal models, such as rodents, to humans. I will discuss recent progress in optogenetics in primates and give a glimpse on putative medical applications with a focus on bidirectional neuroprosthetic devices. Neuroprosthetics is a field which aims to help people who lost control over one or more of their limbs due to a spinal cord injury, a neural disease, a stroke, or an amputation. By reading out signals directly from cortex, decoding them, and using these decoded signals to control a prosthetic device we can bypass the faulty circuits. I will describe the opportunities which optogenetics provide for writing in tactile information. This could allow the users of neural prostheses to not only control a robotic arm but also to feel what they are grasping.