Neurotechnologies to restore hand functions

Reaching and manipulating objects are crucial tasks that allow proactive interaction with our surroundings. However, these functions are lost after neurological disorders or traumatic events that cause hand paralysis. Neuroprosthetic technologies are medical devices that can substitute or restore a damaged motor or sensory modality. In this Review, we discuss how advanced technological modules can be used to restore hand functions in subjects with paralysis. First, we illustrate how the subject's intended hand functions can be extracted by deciphering their cortical activity or residual body movements. Next, we describe how invasive and non-invasive electrical stimulation of neural or muscular structures can activate different hand muscles to restore functional movements. We then provide examples of 'brain-to-body' interfaces that can decode the hand motor intent from brain signals and activate muscles accordingly, allowing voluntary control of movements while bypassing the neurological issue. Finally, we discuss the future steps required for the clinical translation of these technologies.