The performance of robotic and prosthetic hands in unstructured environments is severely limited by their having little or no tactile information compared to the rich tactile feedback of the human ...

When sharing load among multiple muscles, humans appear to select an optimal pattern of activation that minimizes costs such as the effort or variability of movement. How the nervous system achieves this behavior, however, is unknown. Here we show that contrary to predictions from optimal control theory, habitual muscle activation patterns are surprisingly robust to changes in limb biomechanics. We first developed a method to simulate joint forces in real time from electromyographic recordings of the wrist muscles. When the model was altered to simulate the effects of paralyzing a muscle, the subjects simply increased the recruitment of all muscles to accomplish the task, rather than recruiting only the useful muscles. When the model was altered to make the force output of one muscle unusually noisy, the subjects again persisted in recruiting all muscles rather than eliminating the noisy one. Such habitual coordination patterns were also unaffected by real modifications of biomechanics produced by selectively damaging a muscle without affecting sensory feedback. Subjects naturally use different patterns of muscle contraction to produce the same forces in different pronation–supination postures, but when the simulation was based on a posture different from the actual posture, the recruitment patterns tended to agree with the actual rather than the simulated posture. The results appear inconsistent with computation of motor programs by an optimal controller in the brain. Rather, the brain may learn and recall command programs that result in muscle coordination patterns generated by lower sensorimotor circuitry that are functionally “good-enough.”

One of the major problems in the design of neurophysiologiv extracellular microelectrodes is the application and selective removal of the insulation. In addition to the usual problems of achieving pin-hole-free coatings and reproducible tip exposures and impedances, chronic electrode designshave the additional requirement of maintaining megohm levels of electrical isolation for months in vivo. A method of insulating finely tapered microelectrodes with complicated shapes by vapor condensation of Parylene-C is presented, along with a method for exposing controlled, reproducible lengths of their tips. In vivo and in vitro impedance tests and unit records obtained over 100 days in monkey motor cortex are presented. The electric arc process used to expose Parylene-covered iridium and tungsten microelectrodes is found to give cleaner recording surfaces with impedances lower than those obtainable with previously described methods. Chronic iridium microelectrodes so fabricated have recorded unit potentials and maintained constant impedances for over 4 months in vivo.