Characterizing Evoked Movement Patterns and Connectivity in Sensorimotor Cortex After Sensory Loss in Squirrel...

Sensory feedback is crucial for movement execution, especially in the highly specialized skilled hand use in humans and other primates. Extensive sensory loss of tactile and proprioceptive inputs from the hand initially results in severe motor deficits, but recovery occurs gradually over time. To determine how sensory loss from one hand affects evoked forelimb movements from sensorimotor cortical areas, lesions were selectively placed in the ascending somatosensory pathway in the dorsal column in the cervical spinal cord (C5, DCL) of three squirrel monkeys. After 1 year of postlesion recovery, we examined the long-term effects of DCL on motor response patterns evoked by long-train intracortical microstimulation (LT-ICMS) from the hand cortex in primary motor cortex (M1) and somatosensory areas 3a, 3b, and 1 in both control and DCL groups. Somatosensory receptive fields were mapped primarily to define the borders of area 3b, as well as to compare somatosensory responses with motor responses after DCL. Corticocortical connections were investigated by injecting neuroanatomical tracers into the sensory-deprived forelimb regions of 3b and M1. We found that after somatosensory loss and compensation, LT-ICMS-evoked movement maps for M1 and deprived somatosensory areas did not show statistically detectable effects of DCL. Results were consistent with our earlier findings of the effects of long-term recovery from DCL on somatosensory response maps and connections among somatosensory areas. We now show that the effects of long-term DCL on evoked motor responses in somatosensory cortex were limited, while the connections between M1 cortex and somatosensory cortical areas were more widespread.