SUMMARYBackgroundPeople with chronic tetraplegia due to high cervical spinal cord injury (SCI) can regain limb movements through coordinated electrical stimulation of peripheral muscles and nerves, known as Functional Electrical Stimulation (FES). Users typically command FES systems through other preserved, but limited and unrelated, volitional movements (e.g. facial muscle activity, head movements). We demonstrate an individual with traumatic high cervical SCI performing coordinated reaching and grasping movements using his own paralyzed arm and hand, reanimated through FES, and commanded using his own cortical signals through an intracortical brain-computer-interface (iBCI).MethodsThe study participant (53 years old, C4, ASIA A) received two intracortical microelectrode arrays in the hand area of motor cortex, and 36 percutaneous electrodes for electrically stimulating hand, elbow, and shoulder muscles. The participant used a motorized mobile arm support for gravitational assistance and to provide humeral ab/adduction under cortical control. We assessed the participant’s ability to cortically command his paralyzed arm to perform simple single-joint arm/hand movements and functionally meaningful multi-joint movements. We compared iBCI control of his paralyzed arm to that of a virtual 3D arm. This study is registered with ClinicalTrials.gov, NCT00912041.FindingsThe participant successfully cortically commanded single-joint and coordinated multi-joint arm movements for point-to-point target acquisitions (80% – 100% accuracy) using first a virtual arm, and second his own arm animated by FES. Using his paralyzed arm, the participant volitionally performed self-paced reaches to drink a mug of coffee (successfully completing 11 of 12 attempts within a single session) and feed himself.InterpretationThis is the first demonstration of a combined FES+iBCI neuroprosthesis for both reaching and grasping for people with SCI resulting in chronic tetraplegia, and represents a major advance, with a clear translational path, for clinically viable neuroprostheses for restoring reaching and grasping post-paralysis.
These results demonstrate the potential for an intracortical BCI to be used immediately after deployment by people with paralysis, without the need for user learning or extensive system calibration.
Recall performance improves as the opportunities for study increase in number. This phenomenon is the repetition effect. A basic assumption of theories that emphasize the role of encoding variability in learning is that greater variability in encoding processes or context from one presentation to the next tends to improve memory performance. In contrast, theories that emphasize the role of organization in learning propose that encoding constancy is important because organizational structures in memory must be maintained as learning progresses. Four experiments are described that demonstrate that under certain conditions, encoding constancy results in better recall performance than encoding variability. In Experiments 1 and 2 mnemonic devices were used to form one or more retrieval paths to each item. In Experiment 3 items were presented in one or more semantic contexts, and in Experiment 4 one or more semantic-orienting tasks were used. A model is proposed in which encoding variability can result in optimal recall performance when only one code for an item is formed.
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