Abstract
Real-time brain-machine interfaces (BMI) have focused on either estimating the continuous movement trajectory or target intent. However, natural movement often incorporates both. Additionally, BMIs can be modeled as a feedback control system in which the subject modulates the neural activity to move the prosthetic device towards a desired target while receiving real-time sensory feedback of the state of the movement. We develop a novel real-time BMI using an optimal feedback control design that jointly estimates the movement target and trajectory of monkeys in two stages. First, the target is decoded from neural spiking activity before movement initiation. Second, the trajectory is decoded by combining the decoded target with the peri-movement spiking activity using an optimal feedback control design. This design exploits a recursive Bayesian decoder that uses an optimal feedback control model of the sensorimotor system to take into account the intended target location and the sensory feedback in its trajectory estimation from spiking activity. The real-time BMI processes the spiking activity directly using point process modeling. We implement the BMI in experiments consisting of an instructed-delay center-out task in which monkeys are presented with a target location on the screen during a delay period and then have to move a cursor to it without touching the incorrect targets. We show that the two-stage BMI performs more accurately than either stage alone. Correct target prediction can compensate for inaccurate trajectory estimation and vice versa. The optimal feedback control design also results in trajectories that are smoother and have lower estimation error. The two-stage decoder also performs better than linear regression approaches in offline cross-validation analyses. Our results demonstrate the advantage of a BMI design that jointly estimates the target and trajectory of movement and more closely mimics the sensorimotor control system.
Highlights
Unlike many brain-machine interfaces (BMI) motor tasks in which the subject can freely move until reaching a target, this task required the monkey to reach the correct target without touching any of the incorrect targets under a limited time constraint
A performance measure used in these experiments was the acquisition accuracy, which is the percentage of trials on which the task is successfully completed
We found that the two stages of the BMI performed in a complementary manner to achieve its overall accuracy; the correct target predictions could compensate for the inaccurate performance of the kinematics decoder and the ongoing trajectory estimation could correct the incorrect target predictions
Summary
There has been a large body of work in the past decade on realtime brain-machine interfaces (BMI) demonstrating that neural signals from the motor cortical areas can be used to control computer cursors or robotic arms in human and non-human primates [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22] One type of such BMIs, which comprises most of this work, aims to estimate a continuous trajectory—for example the position of a computer cursor on the screen moving towards a visual target [1,2,3,4,5,6,7,8,9,10,11,12,13,14,19]. We presented promising results of a real-time BMI that jointly decodes the target and trajectory in [52,53,54]
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