Biomedical Engineering Blog

Biomedical Engineering

The Biomedical Engineering blog is the place for conversation and discussion about topics related to engineering principles of the medical field. Here, you'll find everything from discussions about emerging medical technologies to advances in medical research. The blog's owner, Chelsey H, is a graduate of Rensselaer Polytechnic Institute (RPI) with a degree in Biomedical Engineering.

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A Sense of Touch for Those with Prosthetic Limbs

Posted October 26, 2011 4:26 PM by Chelsey H

The field of prosthetics has made leaps and bounds towards developing artificial limbs that look, feel and move like real limbs. This has come as a blessing to people across the world who have lost their limbs from disease, trauma or congenital deformities. While there has been great success in creating limbs which move and function by thought, patients are still left without their ability to feel what they are touching or reaching for. This need has led a group of scientist at Duke University to work on a program that could one day provide those with prosthetic limbs or even quadriplegics with a virtual send of touch. The study was published in the journal Nature on October 5, 2011.

A virtual sense of touch would give the user of a prosthetic limb, like this hand, the ability to "fee" how are they were gripping or the buttons they were pushing. (Photo: Mechanical Engineering)

Evolving technology uses brain-machine interfaces to move the prosthetic. Brian-machine interfaces use neuronal activity recorded from the brain to establish direct communication with external actuators, but the new device is considered a brain-machine-brain interface (BMBI) since it controls the reaching movements of an actuator as well as allowing for the signaling of artificial tactile feedback through intracortical microstimulation (ICMS) of the primary somatosensory cortex.

The Discovery

Touch is a critical sense for the health, safety and wellbeing of a person. Amputees lose their ability to sense temperature, texture, position in space, etc. for an object they are trying to grip. Sliman Bensmaia, a neuroscientist at the University of Chicago, says "Sensory feedback is critical to doing anything; even mundane tasks like picking up a cup require a great deal of concentration so the wearer does not drop or crush it."

Current research uses monkeys as the test subjects for the new technology. Electrodes are placed on the monkey's brain which allows them to control a virtual hand, which they see through a computer screen, with their brain. The monkey uses a joystick to hit the target on the screen with the virtual hand (avatar) and electrical pulses are passed through another electrode on the brain, simulating a sense of touch. The objects on the screen were identical but designed to have different artificial textures that could be identified as the virtual hand explored them. Texture was identified using stimulation through microwave arrays implanted in a part of the brain's cortex responsible for sensing touch. Each texture had a unique electrical pattern corresponding to it. Through positive reinforcement, monkeys were able to distinguish the target's textures to select the correct one in as little as four weeks.

A video of the experiment can be seen here.

Another experiment had the monkeys receive the same tactile feedback as they tried to control the virtual hand with just their thoughts. While less accurate, there was improvement with time. The hope of this technology is that in the future, severely paralyzed patients will have their ability to reach for and touch objects restored.

Miguel Nicolelis at Duke University Medical Center says that the brain-machine interfaces will only be clinically useful if they use bidirectional signals, with both sensory feedback from the device and motor commands from the user. But the success of a BMBI shows that processes of sensing and responding to tactile sensations can be combined to decode motor intentions and tactile messages simultaneously.

The Next Step

The sense of touch still needs to be incorporated into real prosthetics. The group hopes to build a pressure sensor that will be used to generate similar tactile feedback about real-world objects. Nitish Thakor, a biomedical engineer at Johns Hopkins University, says the experiment not only demonstrates the feasibility of adding touch, but shows that the monkeys can learn a task using these coupled signals. The caveat, he adds, is that textures in the real world are much more complex, as are body movements, and "whether this is scalable remains to be seen."

"The remarkable success with non-human primates is what makes us believe that humans could accomplish the same task much more easily in the near future," Nicolelis said.

Resources

Brain Power Moves Virtual Objects

Giving Prosthetics a Sense of Touch

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