Although only a few types of artificial neurons were developed, none of them were truly practical for neuro prostheses. One of the biggest problems is that the neurons in the brain communicate very accurately, but the electrical output from a typical electrical neural network is not able to target specific neurons. To overcome this problem, the team converted electrical signals into light. Advances in optogenetics have made it possible to precisely target neurons in a very small area of the biological neural network.
Optogenetics is a technology that takes advantage of several light-sensitive proteins found in algae and other animals. The insertion of these proteins into neurons is a kind of hack; as soon as they appear, the light from the neuron will make it active or inactive, depending on the type of protein.
In this case, the researchers used proteins that were activated by special blue light. In their experiment, they first converted the electrical output of a neural network into a checkered pattern of blue and black squares. Then they illuminated this pattern by a square of 0.8 by 0.8 mm of the biological neural network growing in the cup. Inside this square, only neurons directly activated by the light of blue squares were directly activated.
Spontaneous activity in cultured neurons causes synchronous activity, which follows a certain rhythm. This rhythm is determined by how neurons are related to each other, the types of neurons and their ability to adapt and change.
They set up an artificial neural network to use several different rhythms until they found a better match. Groups of neurons were assigned to specific pixels in the image grid, and then rhythmic activity was able to change the visual pattern that was illuminated by cultured neurons. Light patterns were shown on a very small area of cultured neurons, and researchers were able to test local reactions, as well as changes in the global rhythms of the biological network.
The team hopes that future prostheses using their system will be able to replace damaged brain circuits and restore communication between brain regions.
Live stream of the Microsoft Build 2020 conference.
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