| Popis: |
Intracortical brain-computer interfaces (iBCIs) can restore functional upper limb movements to individuals with chronic tetraplegia by converting neural signals into the movement of an external effector, such as a robotic limb or paralyzed arm reanimated through functional electrical stimulation (FES). While most human-operated iBCIs have extracted intended kinematic parameters such as position and velocity from the motor cortex, restoring natural grasping and object interaction capabilities also requires the control of kinetic parameters such as force. The development of hybrid iBCIs that incorporate both movement kinematics and kinetics requires an understanding of how kinetic information is represented within the human motor cortex, and how this representation is affected by additional motor and non-motor parameters during intended actions. Here, we investigated in a person with chronic tetraplegia how motor cortical neural activity was modulated by three discrete force levels over a range of volitional states (i.e., observed, imagined, and attempted forces) and hand and arm postures.Four major findings emerged from this work. First, this study showed quantitative, electrophysiological evidence that force-related activity persists in motor cortex, even after tetraplegia, in three individuals. Second, it showed that neural force representation depends on volitional state. Attempted forces were represented to a greater degree, and were more accurately predicted from neural data, than observed and imagined forces. Third, we found that attempted forces had both grasp-independent and grasp-dependent neural representations. Specifically, while attempted forces could be predicted from the neural activity at levels above chance across up to five hand and arm postures in two participants, these arm and hand postures significantly impacted the accuracy of attempted force predictions. Finally, this study showed that force-related information was represented to a lesser degree than other parameters, including volitional state and grasp, possibly due to deafferentation-induced changes in somatosensory feedback.This study provides relevant information towards the development of a hybrid kinetic and kinematic iBCI. While the study results indicate that incorporating force control into iBCIs is feasible, force iBCIs will likely need to account for the impacts of additional motor and non-motor parameters in order to maximize performance. |
