Bio-neural energy
From Memory Alpha, the free Star Trek reference.
Bio-neural energy is the electrical activity generated by an organic nervous system, the absence of which usually constitutes death. In 2371 Commander Chakotay's bio-neural energy was displaced by trianic energy beings known as the Komar. Although he was pronounced brain-dead by USS Voyager's Emergency Medical Hologram, his disembodied consciousness remained intact, able to navigate and take control of other lifeforms. (VOY: "Cathexis")
