"A lot of patients that are motor-disabled might have partial sensory feedback," said Nicholas Hatsopoulos, PhD, Associate Professor and Chair of Computational Neuroscience at the University of Chicago.
"That got us thinking that maybe we could use this natural form of feedback with wearable robots to provide that kind of feedback."
In the experiments, monkeys controlled a cursor without actively moving their arm via a device that translated activity in the primary motor cortex of their brain into cursor motion.
While wearing a sleeve-like robotic exoskeleton that moved their arm in tandem with the cursor, the monkey's control of the cursor improved, hitting targets faster and via straighter paths than without the exoskeleton.
"We saw a 40 percent improvement in cursor control when the robotic exoskeleton passively moved the monkeys' arm," Hatsopoulos
Those troubles helped researchers realize the importance of proprioception feedback, Hatsopoulos
"In the early days when we were doing this, we didn't even consider sensory feedback as an important component of the system," Hatsopoulos
"We really thought it was just one-way: signals were coming from the brain, and then out to control the limb.
It's only more recently that the community has really realized that there is this loop with feedback coming back."
Reflecting this loop, the researchers on the new study also observed changes in the brain activity recorded from the monkeys when sensory feedback was added to the set-up.
With proprioception feedback, the information in the cell firing patterns of the primary motor cortex contained more information than in trials with only visual feedback, Hatsopoulos
said, reflecting an improved signal-to-noise ratio.
The improvement seen from adding proprioception feedback may inform the next generation of brain-machine interface devices, Hatsopoulos
Already, scientists are developing different types of "wearable robots" to augment a person's natural abilities.
Combining a decoder of cortical activity with a robotic exoskeleton for the arm or hand can serve a dual purpose: allowing a paralyzed subject to move the limb, while also providing sensory feedback.
To benefit from this solution, a paralyzed patient must have retained some residual sensory information from the limbs despite the loss of motor function -- a common occurrence, Hatsopoulos
said, particularly in patients with ALS, locked-in syndrome, or incomplete spinal cord injury.
For patients without both motor and sensory function, direct stimulation of sensory cortex may be able to simulate the sensation of limb movement.
Further research in that direction is currently underway, Hatsopoulos
"I think all the components are there; there's nothing here that's holding us back conceptually," Hatsopoulos
Aaron J. Suminski, Dennis C. Tkach, and Hatsopoulos
and Andrew H. Fagg.
The additional sensory information resulted in the cursor hitting the target faster and more directly. (Credit: Courtesy, with permission: Hatsopoulos
, et al.
The Journal of Neuroscience