A research published in the journal Science Translational Medicine shows that the nervous system has the capacity to encode the intensity of tactile perception. The work continued the research suggesting that different patterns of electrical signals give amputees familiar sensations, such as the touch of a cotton ball or the press of the tip of a ball-point pen.
Keith Vonderhuevel is one of the two amputees testing a prosthetic system that allows him to feel the intensity of pressure in the prosthetic hand, similar to the sensation his brain produces for the intact hand, as the new study investigated.
The research, conducted by scientists at the Case Western Reserve University, the Louis R. Stokes Cleveland VA Medical Center and the University of Chicago, could forever change the future of amputees, provided that the results show the conclusions could be extended to a larger target.
"It feels like a light pressure. The harder I squeeze, the stronger that pressure gets," said the man, who lost his right arm below the elbow in a job-related accident over 11 years ago.
Vonderhuevel and the other trial patient were allowed to take the prosthetic hand at home for use in a domestic environment outside of the laboratory and to see whether the experimental hands make a difference in their everyday life.
Testing The Hypotheses
In the study, the scientists discovered that the two trial patients can feel up to 20 different levels of intensity that can be interpreted as pressure.
The testing method was conducted using three different steps: determining the smallest difference the two patients could perceive as a distinct pressure; rating the intensity of the signals; and comparing the intensity of the patients' sensations with the pressure they measured in the intact hands.
Sliman Bensmaia, senior author of the study, predicted the results of the testing, suggesting — based on previously conducted research — that the population spike rate (inside the nerves) would be directly related to the intensity the patients perceived the stimuli had.
The study confirmed the hypotheses, proving that the activation charge is highly similar to the spike rate taking place in the nerve bundle. These conclusions bring a better understanding of the hands' perceptions, which could be used in the development of future prosthetics, mimicking the sensations on a more accurate level.
A more realistic sensation of feeling could be created using the data from this research, which would ultimately lead to prosthetics, creating highly similar sensations in the brain to the ones transmitted by the intact hands of the patients.
"This may enable us to retrieve tactile information remotely, the way we use cameras to see remotely," explained Dustin Tyler, primary investigator of the research.