Enabling Sensory Discrimination in Upper-limb Amputees Studied by RNEL and HERL Teams
December 2, 2022
In October 2022, experts from the University of Pittsburgh Departments of Physical Medicine and Rehabilitation and Bioengineering – as well as the Rehab Neural Engineering Labs and Human Engineering Research Labs – published “Closed-loop stimulation of lateral cervical spinal cord in upper-limb amputees to enable sensory discrimination: a case study” in Scientific Reports.
Modern myoelectric prosthetic hands have multiple independently controllable degrees of freedom, but they require constant visual attention to use effectively. Somatosensory feedback provides information not available through vision alone and is essential for fine motor control of our limbs. Similarly, stimulation of the nervous system can potentially provide artificial somatosensory feedback to reduce the reliance on visual cues to efficiently operate prosthetic devices.
The team has shown previously that epidural stimulation of the lateral cervical spinal cord can evoke tactile sensations perceived as emanating from the missing arm and hand in people with upper-limb amputation. In this case study, two subjects with upper-limb amputation used this somatotopically-matched tactile feedback to discriminate object size and compliance while controlling a prosthetic hand.
With less than 30 minutes of practice each day, both subjects were able to use artificial somatosensory feedback to perform a subset of the discrimination tasks at a success level well above chance. Subject 1 was consistently more adept at determining object size (74% accuracy; chance: 33%) while Subject 2 achieved a higher accuracy level in determining object compliance (60% accuracy; chance 33%).
In each subject, discrimination of the other object property was only slightly above or at chance level, suggesting that the task design and stimulation encoding scheme are important determinants of which object property could be reliably identified. The team’s observations suggest that changes in the intensity of artificial somatosensory feedback provided via spinal cord stimulation can be readily used to infer information about object properties with minimal training.
Research Team
Michael Boninger, MD
Jennifer Collinger, PhD
Lee Fisher, PhD
Robert Gaunt, PhD
Eric Helm, MD
Ameya Nanivadekar, PhD
Santosh Chandrasekaran, PhD
