Proprioception, Motor Imagery, and the Parietal Lobe: An Experimental Design for Patients with Locked-in Syndrome

Neuroprosthetics, a promising technology for patients with Locked-in Syndrome (LIS), works by decoding brain activity from the motor cortex while patients engage in motor imagery. However, whether LIS patients can engage in motor imagery is still controversial. Moreover, a subset of LIS patients lacks proprioceptive input, a type of sensory feedback important for motor learning. We speculate that the lack of proprioception may act as a bottleneck for LIS patients to engage in motor imagery. Here, I explain recent findings in LIS pathology and its relationship with motor imagery. Then, I provide a comprehensive literature review including behavioral and neuroimaging evidence for motor imagery in healthy brains. Finally, I propose an experimental design to investigate if proprioception is essential for LIS patients to engage in motor imagery. Two separate, but related tasks are proposed, a modified hand rotation task and a neuroprosthetic control task. We predict that a subset of LIS patients, those who lack proprioceptive input to the parietal lobe, will not be able to engage in motor imagery nor will they be able to control the neuroprosthetic arm after a short motor imagery training, while those with spared proprioceptive input will. We speculate, after reviewing underlying neural mechanisms recruited for motor imagery in healthy subjects, that cortical volume loss in frontoparietal areas, specifically the superior parietal lobe, and an injured medial lemniscus tract in such LIS patients might explain impaired motor imagery. Findings suggest that proprioception plays an important role in sensorimotor learning and has practical implications for future technological advances in neuroprosthetics