Hess used brain stimulation techniques developed in the late 1920s. Using electrodes, Hess stimulated the brain at well-defined anatomical regions. This allowed him to map regions of the brain to specific physiological responses. He developed a special technique he called "interrupted direct-current (DC) stimulation" which used stimuli of long duration (typically 12.5 or 25 ms) with ramp-like upward and downward slopes. Also, the stimuli were rather weak (around 0.5–1.5 V) and of low frequency (2–12 Hz, usually 8 Hz) and he used very fine electrodes with a diameter of 0.25 mm.