electrodes and circuitry for monitoring and stimulating the exterior of the human body , comprising delivering stimulation pulses to stimulation electrodes applied to the exterior of the body , detecting an electrical potential at monitoring electrodes applied to the exterior of the body , positioning at least a first and second monitoring electrode at locations at which an electrical artifact caused by the electrical stimulation pulses is substantially cancelled in a signal formed from the electrical potentials detected at the first and second monitoring electrodes .