Dr. Giulio Tononi, distinguished chair in consciousness science at the University of Wisconsin, and colleagues are adapting information theory to build a “consciousness meter” that doctors can use to measure consciousness.

Tononi and his colleagues have been expanding traditional information theory to develop an “Integrated Information Theory.” Consciousness, he says, is nothing more than integrated information, measurable in bits.

It is possible, the researchers have shown, to calculate how much integrated information there is in a network. Tononi has dubbed this quantity “phi.” Networks gain the highest phi possible if their parts are organized into separate clusters, which are then joined.

To test the theory, Tononi is placing a small magnetic coil on the heads of volunteers. The coil delivers a pulse of magnetism lasting a tenth of a second. The burst causes neurons in a small patch of the brain to fire, and they in turn send signals to other neurons, firing in a complex pattern across large areas of the brain that can be measured with a mesh of scalp electrodes.