A new study by experts at the University of Chicago paves the way for the development of prosthetic limbs that will "feel" touch and provide the important sense of touch to paraplegics and amputees.
Robotic limbs like... alive
The study, published in the journal Proceedings of the National Academy of Sciences, takes a significant step toward technology that will allow robotic limbs to have dexterity and behave like "life.".
Slimane Bensmayah and his colleagues have developed a new model for transmitting the sense of touch to the brain by bypassing conventional pathways. The researchers hope that this model will form the basis for the development of prosthetic limbs that feel touch just like natural ones.
The experiment on monkeys
Initially, scientists trained rhesus macaque monkeys to focus their gaze in different directions depending on whether someone touched their index or ring finger.
They then placed microelectrodes in a region of the brain called the primitive somatosensory cortex. This area represents a complete map of the body, with each neuron responsible for firing each time someone touches a different spot on the skin.
Microelectrodes record the activity patterns of neurons – they can even be used in reverse to electrically stimulate neurons if needed.
The researchers recorded exactly where in the primitive somatosensory cortex activity was recorded when they touched the index or ring finger of the experimental animals.
Reaction through electrical stimulation
Having recorded the activity patterns, they continued by stimulating the brain themselves and following the same patterns. They saw that the monkeys reacted as if someone had touched them – they focused their gaze in the direction they had been taught to look in response to the touch on either their index or ring finger.
In similar experiments, monkeys fitted with a prosthetic hand that relayed information to their brains via microelectrodes were also able to distinguish between touches of different intensities. "Information about the location and intensity of a touch is usually not available visually or is not sufficient to guide the movements of people with prosthetic limbs," said Dr. Bensmaya. "However, this information is critical. If you don't have it, you can drop and damage objects you are holding.".
Future "gift" of the touch of a loved one
The researcher hopes that one day sensors on prosthetic limbs will be able to transmit signals to implants placed in patients, which will separate the correct patterns of electrical impulses and transmit them to the brain, which will give the robotic limbs a sense of touch. Such prosthetic limbs of the future will make patients feel their artificial limb as a more natural part of their body, allowing them to better interact with their environment. “Perhaps these limbs will help a person touch a loved one for the first time.”.
Although implantable electrodes have been used in humans to date, Dr. Bansmaya notes that they come with limitations. The implants must be safe and durable enough to remain in the brain for a long time, but also "adaptive" enough to continue to function as the brain ages over time.
Promising biomimetic approach
Despite the obstacles, Lee Miller of Northwestern University in Illinois says Bansmay's biomimetic approach holds promise for the future of prosthetic limbs, which currently have limited sensory capabilities. "This approach is trying to replicate a natural pattern of sensory activity, and that's very important," he says. "The best approach to giving prosthetic limbs the 'decoding' of touch is to mimic the brain's own signaling as closely as possible.".
Source: tro-ma-ktiko.blogspot.gr
