Somatosensory encoding with cuneate nucleus microstimulation: Effects on downstream cortical activity

High-performance neuroprostheses designed to reanimate a paralyzed limb following spinal cord injury must restore both movement and sensation. For the latter goal, we are developing a novel strategy focused on encode sensations using microstimulation of the cuneate nucleus (CN) of the brainstem. Here, we characterized the temporal dynamics of downstream cortical excitation and inhibition in response to CN microstimulation in a macaque. A single CN stimulus pulse evoked a fast (7 ms) excitatory response in primary somatosensory cortex (S1) followed by an inhibitory period lasting until 50 ms. The S1 response to a second CN pulse within this inhibitory period was drastically attenuated. Following the inhibition, S1 unit activity rebounded with a prolonged excitatory phase lasting until 800 ms. Within this second excitatory phase were rhythmic peaks of increased unit activity with an alpha-band frequency (8-14 Hz). The rhythmic excitation was specific for perigranular laminae and was stimulus-amplitude dependent. The results show a complex cortical response to CN stimuli and can guide future design of CN stimulus patterns to evoke salient percepts.