A technique for amplifying and recording the fluctuations in electrical voltage in a living brain using electrodes attached to key positions on the person's head; this technique has proved to be particularly important for sleep-research (and thus also for research on dream-telepathy), where characteristic brain waves have been identified and related to the successive stages of sleep. [From the Greek enkephalos, "the brain," derived from en, "within," + kephale, "the head," + graphein, "to write"]