Simulation analysis of the ability of different types of multi-electrodes to increase selectivity of detection and to reduce cross-talk

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Selectivity of different one- and two-dimensional multi-electrodes and their ability to reduce cross-talk were analyzed. Signals from an individual motor unit (MU) were calculated as a single convolution of intracellular action potential (IAP) first temporal derivative and spatially filtered MU impulse response. It was shown that the uptake area (irrespective of the way it was defined) could not characterize electrode properties reliably because its estimate depended on the source parameters. Due to the different decline of individual phases of MU signals with depth, electrode should provide higher spatial and temporal resolution of the main phases for better selectivity and greater suppression of the terminal phases for cross-talk reduction. A two-dimensional normal double differentiating (NDD) electrode provided almost the same or slightly lower selectivity but weaker reduction of cross-talk than a longitudinal double differentiating (LDD) electrode. A transversal double differentiating (TDD) electrode provided a lower selectivity and weaker reduction of cross-talk than a LDD electrode. A new, BiTDD multi-electrode (performing difference between signals detected by two TDD electrodes) provided the best selectivity and reduction of cross-talk. To obtain the smallest cross-talk, a BiTDD electrode should be positioned above the end-plate region, while LDD, TDD, or NDD electrodes—above the ends of muscle that produced it. Signal differentiation improved selectivity but increased cross-talk.