The electrical pacemaker (Inch Inc., Brooklyn, NY) used in this work is a self-contained portable device with integrated circuits, housed in a box about eight inches on all sides. EI is delivered as 10-second bursts of bipolar, constant-current, square-wave pulses in 20% duty cycles. A 20% duty cycle consists of a pulse of current at the given amperage lasting 20% of the cycle, followed by a period without current for the remaining 80% of the cycle. The number of cycles per second defines the frequency in Hertz (Hz). Because the duty cycle is constant at 20%, a 10-second burst always delivers current for a total of 2 seconds, with the frequency determining the length and number of individual pulses, in milliseconds (msec), during the burst.