Reanimating paralyzed limbs - Coping with spatially distributed, multimodal systems

Sensory prostheses generally require dense multichannel interfaces in a small place that is difficult to access but mechanically protected. Motor prostheses must activate a relatively modest number of muscles distributed widely over limbs subject to constant motion and external impacts. Sensory prostheses require high data rates to recreate complex temporospatial patterns of neural activity while muscles are unidimensional low-pass filters. Sensory prostheses generally need one sophisticated interface for stimulation while sensorimotor prostheses require a wealth of command and feedback signals employing different electrical and mechanical sensing modalities. Sensory prostheses do as little signal processing as necessary to enable the brain to do the difficult perceptual computations while sensorimotor prostheses must replace the functionality of motor planning and coordination centers whose normal functions we barely understand. Sensory deficits (e.g. deafness, blindness) tend to affect large numbers of patients in homogeneous and stable ways while motor deficits come in a much wider variety and change over time due to neural and muscular plasticity. We are just starting to assemble the diverse armamentarium of implantable interfaces, control strategies and fitting tools that will be needed to treat motor disabilities successfully.