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Sensory Feedback Improves Brainwave Control of Portable, Lightweight Hand Exoskeleton

EPFL researchers are developing a portable and lightweight hand exoskeleton that can be easily controlled through brainwaves. The novel device not only improves the performance of brain-machine interfaces, but also restores functional grasps for the physically impaired.

This extremely portable and lightweight hand exoskeleton is projected to assist the physically impaired with day-to-day living. These are the hopes of Luca Randazzo, an EPFL scientist who is creating the exoskeleton with the Defitech Chair in Brain-Machine Interface, headed by José Millán. The results of the study have been reported in the January edition of IEEE Robotics and Automation Letters.

While their laboratory at Campus Biotech in Geneva is fitted with commercial exoskeletons and gait machines for walking assistance, Randazzo began with the rudiments. “When I arrived at the lab, the first thing I added was a sewing machine so that I could develop wearable devices,” he explains.

Lightweight, Portable and Adaptable Exoskeleton

Quickly and easily strapped to the joints with Velcro, patients are fitted with the lightweight hand-exoskeleton within a few minutes. Metal cables serve as soft tendons along the back-side of all fingers, leaving the palm free so as to increase the sensations felt by the hand. Motors are integrated in a chest-pack that push and pull on the different cables, extending the fingers when the cables are pulled and flexing them when pushed.

The exoskeleton is adaptable by design, making it possible to select the control interface according to the patient’s residual physical ability. Following which, the control interface can be selected from of a wide range of systems, spanning from eye-movement monitoring for the severely paralyzed, residual muscular activity of the damaged limb, smartphone-based voice interfaces, through to reading brainwave activity with a headset.

Unexpected Brain Signal Enhances Exoskeleton Control

The researchers decided to explore the brainwave-control of the exoskeleton through an EEG headset that is capable of measuring the users’ brainwaves as they utilized the exoskeleton. They observed that exoskeleton-induced hand motions trigger brain patterns, which are typical of healthy hand motions. However, the team also found that the hand motions induced by the device, together with a user-driven brain-machine interface, resulted in unusual brain patterns that could in fact make it possible to control the device.

Motor cortex refers to the part of the brain that controls body movement. This region is actually divided into a right- and a left-hand side. During control of the left hand, the right motor cortex is mostly active, while the left motor cortex is active during control of the right hand. This is a property of the nervous system known as contralateral control – contra for opposite and lateral for side.

As predicted, the researchers noticed this contralateral brainwave activity in patients who passively received exoskeleton-induced hand motion. However, they also observed that reliable same-side patterns also emerged in the brainwave data when the patients were asked to regulate the hand-exoskeleton with their brainwaves.

To put it in simple terms, when the subjects were asked to actively think about shifting the exoskeleton, the region of the brain that usually thinks about regulating the opposite hand was being solicited in the brain as well.

According to the researchers, this brain activity arising from the combination of coherent feedback and voluntary control afforded by the device could be manipulated for enhancing the brain control of these devices.

This enhanced control of the hand-exoskeleton with brainwave activity is most likely due to higher engagement of subjects facilitated by rich sensory feedback provided by the nature of our exoskeleton. Feedback is provided by the user’s perception of position and movement of the hand, and this proprioception is essential.

José Millán

The hand-exoskeleton has been so far tested with patients with disabilities caused by spinal cord injuries and strokes. The next steps involve enhancing the system both for performing tasks at home, for assistive purposes, or even as a device for rehabilitation.

The hope is that by combining seamless human-machine interfaces and portable devices, these kinds of systems could enable and promote functional use in meaningful daily tasks,” adds Randazzo.

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