Researchers at the University of Chicago, Illinois are laying the groundwork for touch-sensitive prosthetic limbs that could transmit a sense of touch to the brain that bypasses regular routes. Partial funding for the project came from the Defense Advanced Research Projects Agency (DARPA), a government group that helps fund innovative devices with a military application. This agency is interested as explosives can lead to injuries that require amputations. From a military perspective, this technology could improve quality of life for veterans who have lost limbs, as well as those in the general public.
To discover the different neural activity patterns associated with the manipulation of objects, the team connected a series of electrodes to the brains of rhesus macaques. Each of the electrodes was connected to a part of the brain which corresponded with the movement of the monkey’s fingers. Then the researchers touched each of the monkeys’ fingers with a specialized pressure device designed to apply a predefined amount of pressure to the fingers. If a monkey accurately determined which of its fingers was pressed, it received a food reward. Recognition of finger pressure was determined by the monkey’s gaze; if the monkey looked at the finger receiving the pressure, the touching sensation was recorded as recognized.
The team were thus able to record what activity occurred in the brain and where using the microelectrodes placed in the macaques’ primary somatosensory cortex. They then reversed the procedure and stimulated the brain using the same patterns of activity and found the monkeys reacted as if they had been touched, fixing their gaze in the direction they had been taught.
The researchers continued the experiment using varying amounts of pressure. The macaques were rewarded when they recognized the different levels of pressure on their fingers. This procedure was also reversed and the monkeys responded to the artificial pressure in the same way as real pressure.
The final part of the study involved studying the brain signals associated with touching and releasing the hands of the monkeys. Certain parts of the monkey’s brain showed a spike in electrical activity when its hand was touched or released. These signals are the ones that allow the brain to think there is something in an animal’s hand. This experiment was also successfully reversed.
It is hoped that these electrical signals could be incorporated into the electronics for a robotic prosthetic limb, and provide sensory feedback to the brain through a neural interface. This would allow prosthetics to have touch sensations.