Generating Artificial Sensations with Spinal Cord Stimulation in Primates and Rodents

For patients who have lost sensory function due to a neurological injury such as spinal cord injury (SCI), stroke, or amputation, spinal cord stimulation (SCS) may provide a mechanism for restoring somatic sensations via an intuitive, non-visual pathway. We have previously shown that rats can learn to discriminate time-varying patterns of epidural SCS. Here we ran additional experiments in rats and conducted a new study in rhesus monkeys trained to discriminate patterns of epidural dorsal thoracic SCS. Based on these results, we constructed psychometric curves describing the relationship between different SCS parameters and the animal's ability to detect the presence of SCS and/or changes in its characteristics. We found that the stimulus detection threshold decreased with higher frequency, longer pulse-width, and increasing duration of SCS. Moreover, we found that monkeys were able to discriminate spatiotemporal patterns (i.e. variations in frequency and location) of SCS delivered through multiple electrodes. Additionally, the analysis of rat data showed that discrimination of SCS-induced sensations obeyed Weber's law of just noticeable differences. These findings suggest that by varying SCS intensity, temporal pattern and location different tactile and/or proprioceptive sensations can be evoked. As such, we posit that SCS can be used to provide intuitive sensory feedback in neuroprosthetic devices.