Development of optimal sensory feedback strategies to maximize function after tetraplegia

Our goal is to develop and optimize novel neurostimulation strategies to restore intuitive and informative somatosensation to people with tetraplegia. Sensory feedback is critical for regulating dexterous grasp during activities of daily living and for emotional connection with loved ones. Neuroprostheses to restore voluntary control of reaching and grasping to users with paralysis will be more likely to achieve clinically-meaningful benefits in independence and quality of life if sensory feedback is integrated into these systems. The central hypothesis is that restoring sensation with intracortical microstimulation (ICMS) of primary somatosensory cortex and/or peripheral nerve stimulation (PNS) will improve performance of brain-controlled grasp tasks. The secondary hypothesis is that paired ICMS and PNS will promote neuroplasticity and enable users to recover some of the below-injury sensory function lost due to spinal cord injury. Three participants with chronic tetraplegia enrolled in an existing clinical trial who have already received chronically-implanted cortical arrays and nerve cuff electrodes will participate in the proposed study. The study has three specific aims: 1) Determine the impact of spatiotemporal ICMS paradigms on perception and function. Novel ICMS encoding schemes that prioritize different neural coding properties and information content of the transmitted touch stimuli will be developed and compared. The perceptual response to each ICMS paradigm will be evaluated with classical psychophysical techniques. Decoders that map cortical activity to desired hand/arm movement commands will be developed and used to perform grasp tasks in virtual reality. The functional utility of each ICMS paradigm will be evaluated and compared. 2) Determine the impact of spatiotemporal PNS paradigms on perception and function. Novel PNS encoding schemes will be developed and their impacts on perception and brain-controlled task performance will be compared. The effect of a PNS training paradigm on below-injury sensory function will also be evaluated. 3) Determine the impact of hybrid (ICMS+PNS) neurostimulation on perception and function. Novel hybrid stimulation paradigms will be developed through systematic investigations of percept integration resulting from manipulations of encoding scheme, electrode contacts, and inter-stimulus timing. Hybrid stimulation will be compared to ICMS-only and PNS-only paradigms in both perceptual characteristics and virtual task performance gains. The effect of a hybrid neurostimulation training paradigm on recovery of below-injury sensory function will also be evaluated. The proposed work will improve our understanding of the perception of neurostimulation applied throughout the sensory nervous system, the benefits of restored sensation on the functional utility of brain-controlled neuroprostheses, and the role of touch information content in these outcomes. This study will also determine the feasibility of a future therapeutic intervention using neurostimulation for below-injury sensory recovery. Study findings have implications for the future development and translation of neuroprostheses to restore sensorimotor function to people with tetraplegia.