How do smart prostheses work?

The principle of operation of neural interfaces

Mikhail Lebedev, Post-science

Today we often encounter the words "neurointerfaces", "neuroprosthesis", and it is already obvious to us that a computer can be connected to the brain. How do neural interfaces work, what opportunities do they open up and what are the prospects for their application?

What is a neuron?

Aristotle reflected on what is responsible for thinking and feeling in the human body, and came to the conclusion that such an organ is not the brain, but the heart: the brain is cold, but the heart is warm; not all animals have a brain, unlike the heart and circulatory system; and if you stick a knife or nail into it then a person will not feel anything – how then can the brain be the center of sensations?

And many believed Aristotle. For centuries, his views had an impact, until two scientists, Camillo Golgi and Santiago Ramon y Cajal, guessed to look at the brain under a microscope. They saw neurons that were of different shapes, with different processes, connected to each other in different ways in different parts of the brain, and realized that it was in the brain that thought processes and processing of feelings and motor commands were going on. Their research marked the beginning of modern neuroscience. Both scientists received the Nobel Prize, but Ramon y Cajal emphasized that the brain consists of neurons and it is possible to build a brain network from them, and Golgi was not close to the idea of such elementary units. He liked the fact that everything is intertwined in the brain and there is a kind of network. Thus, both had somewhat different ideas about the work of the brain, but nevertheless received the Nobel Prize.

Ramon y Cajal's neuronal doctrine can be traced to this day, as can Golgi's theory. And disputes constantly arise: some scientists emphasize the importance of the neuron and the operations it performs, while others highlight the neural network and emphasize the distributed processing of information in the brain.

Neuroscience developed, and for a while Cajal's ideas prevailed: neurons were discovered, it became clear how they are connected and transmit information to each other. And indeed, a neuron is something whole. It consists of a cell body, dendrites receiving information, an axon through which information is sent to other neurons, and synapses – this is the place of contact between two neurons, where information is transmitted from one neuron to another. If you stick to this scheme, then the brain is like an electronic circuit. Neurons can be excitatory and inhibitory. And if you take a certain number of both neurons, connect them and come up with a certain scheme, then they will work as intended.

Everything would have been fine, but then it came to the realization that Golgi was right about something. For example, neurons can form electrical synapses between themselves, through which ions walk quite freely. And the neurons turned out to be not as elementary units as previously thought. For example, in the cerebral cortex, inhibitory interneurons form a network connected by electrical synapses. It has also been found that a neuron, when operating, emits electromagnetic fields that can affect neurons located nearby. This was called efaptic transmission. Now some researchers believe that it may play a certain functional role. 

Capabilities of neurointerfaces

It turns out that we know something, but we don't know much more yet. However, this does not stop the developers of neurocomputer interfaces, who set themselves an ambitious goal: they want to record brain activity, decode it and then use the recorded information from the brain to solve certain tasks. 

There are people with neurological lesions, for example, paralyzed, with spinal cord injuries. Presumably, it is possible to record signals from the brain in such patients, decode this activity and then direct it to a prosthetic arm or leg. Thanks to this, such people will gain the ability to move and feel. 

The possibility of expanding brain functions is also discussed: a person connects to a device that reads his brain activity, which is decoded and sent to a computer, and the computer helps to expand functions. There are even more futuristic ideas for future projects, such as interfaces that involve the brains of several people – information is exchanged.

How the neurointerface works and works

First of all, a human brain is needed, one or more. There should also be sensors that register the electrical activity of the brain: invasive, that is, electrodes implanted in the brain, and non–invasive - electrodes that are placed on the head to record an electroencephalogram, or a special device that records a magnetoencephalogram. What we register – and it is desirable to record as much information as possible – is fed to the decoder. A decoder is a device with a certain mathematical algorithm that is trained to interpret brain activity and is a mini-brain (artificial neural networks are now actively used as decoders). It interprets the recorded information and highlights the signals we are interested in. 

For example, a paralyzed person intends to make movement with a prosthesis. It is necessary to decode the position of the hand that he wants to set to the prosthesis. We select the coordinates of the prosthesis, direct it to the desired point in space, and thus a person controls the movements of the prosthesis by the activity of his own brain with the help of a neurointerface.

The prosthesis can be equipped with various sensors: for example, there are tactile sensors on the fingers of an artificial hand, and when the hand touches objects, this activity can be sent back to the brain, to the sensory departments, in order to cause sensations in a person. We get a prosthesis that is not only controlled by brain signals directly, but can also send information back to the brain in such a way that the person controlling the movements of the prosthesis feels it almost as part of his own body. It is hoped that if a person uses such a prosthesis for a long time, then due to the plasticity of the brain, the device will be indistinguishable from natural parts of the human body. There is also talk that a person may need a third hand in some conditions, and now such ambitious tasks are being set. 

We see the rapid development of neurointerfaces, but we are at the beginning of the path: when we go outside, we still do not see people who control neurointerfaces. All this is still in laboratories or at special screenings. But eventually neural interfaces will enter our lives and become an everyday reality for us.

Portal "Eternal youth" http://vechnayamolodost.ru