Primary motor cortex tuning to intended movement kinematics in humans with tetraplegia.

The relationship between spiking activities in motor cortex and movement kinematics has been well studied in neurologically intact nonhuman primates. We examined the relationship between spiking activities in primary motor cortex (M1) and intended movement kinematics (position and velocity) using 96-microelectrode arrays chronically implanted in two humans with tetraplegia. Study participants were asked to perform two different tasks: imagined pursuit tracking of a cursor moving on a computer screen and a "neural cursor center-out" task in which cursor position was controlled by the participant's neural activity. In the pursuit tracking task, the majority of neurons were significantly tuned: 90% were tuned to velocity and 86% were tuned to position in one participant; 95% and 84%, respectively, in the other. Additionally, velocity and position of the tracked cursor could be decoded from the ensemble of neurons. In the neural cursor center-out task, tuning to direction of the intended target was well captured by a log-linear cosine function. Neural spiking soon after target appearance could be used to classify the intended target with an accuracy of 95% in one participant, and 80% in the other. It was also possible to extract information about the direction of the difference vector between the target position and the instantaneous neural cursor position. Our results indicate that correlations between spiking activity and intended movement velocity and position are present in human M1 after the loss of descending motor pathways, and that M1 spiking activities share many kinematic tuning features whether movement is imagined by humans with tetraplegia, or is performed as shown previously in able-bodied nonhuman primates.