Linear summation of torque produced by selective activation of two motor fascicles.

Linear summation of torque was observed while applying selective activation to two different motor fascicles in the cat sciatic nerve. The excitatory stimulus was applied to two or more contacts housed in a four contact self-sizing spiral cuff electrode. To achieve a linear summation of torque, a delay between the two stimuli that was longer than the length of the facilitatory period but less than the length of the refractory period was used. Using a 900-micros delay between pulses, linear summation of two different torque outputs was successfully achieved in 125 out of 129 trials across five cats. These trials were performed using cuff electrodes that were in place for periods ranging up to 352 days. The results of these studies support the hypothesis that a single self-sizing spiral cuff with multiple contacts and a single lead may be used in place of several muscle-based electrodes each with its own separate lead.