Feelings identical to natural ones
Scientists have made it possible for a patient with paralyzed limbs to feel
Anton Bugaichuk, Naked Science
A group of scientists led by Richard Andersen (California Institute of Technology, USA) made the paralyzed patient, who had lost skin sensitivity, feel again.
To do this, they used microelectrodes that were implanted in the area of the primary somatosensory cortex of the brain.
It is located in the gyrus of the cortex, behind the central furrow. This area has a unique property: the points on its surface correspond to areas of skin throughout the body. It is the somatosensory cortex that processes signals from skin receptors, and a person feels a change in temperature, pressure or pain. The same area is "responsible" for the feeling of one's own body in space.
If the spinal cord is damaged, the connection between the receptors and the somatosensory cortex is severed. With such paralysis, not only mobility is lost, but also the sensitivity of the limbs. The cerebral cortex itself is not affected, but no signals are received to it. Although such an injury is incurable, it is possible to stimulate the cortex directly, and a person will experience sensations similar to natural ones. This effect has been known for a long time, but previously scientists used a rather rude electric shock irritation: sensations appeared unnatural, and with additional "noises" — in the form of tingling or minor electric shocks.
The researchers decided to use microelectrodes implanted in the brain. This approach increased the accuracy of stimulation and allowed to reduce the current strength.
The experiment was carried out on a patient paralyzed below the neck due to spinal cord injury. Two microelectrode implants were implanted in the somatosensory cortex.
S1 is the implant placement area. Drawings from the article by Salas et al. Proprioceptive and cutaneous sensations in humans elicited by intracortical microstimulation (eLife 2018).
Of course, the sensations caused by stimulation were not completely identical to natural ones, but the experiment gave interesting results. Not all electrodes caused sensitivity (46 out of 96, 48%), however, the response was stable, and false "triggers" were not observed. The influence of previous stimulations on subsequent ones was not observed, the reaction was similar to natural: a certain signal is received, as a result, a corresponding sensation arises. There were no complications and pain sensations either during the experiment or after.
The figure on the left (A) shows the zones in which there were sensations of the front (light shades) and back (dark shades) sides of the hand and hand (blue). To the right, it is shown which microelectrodes on the electrode arrays of the implant correspond to these zones. The diagram on the right shows the type of sensations experienced: red shows skin sensitivity, blue — proprioceptive, that is, body sensations in space. As can be seen in the picture, some electrodes caused a mixed sensation. Skin sensations were caused by stimulation of 45% of the electrodes, 32% caused a sensation of movement, and 23% — both types of sensations.
During the experiment, the patient clearly described his feelings, which were diverse and corresponded to natural: pressing, tapping, hand movement.
The experiment clearly showed the advantage of stimulation with implanted microelectrodes — the feelings were almost real and at the same time clear, without "noise". In the future, the research team intends to make a detailed map for electrical stimulation, accurately identifying the areas of the cortex and the corresponding sensations.
The research is of great importance for the development of neurointerfaces and bionic limb prostheses.
Portal "Eternal youth" http://vechnayamolodost.ru