Attempt to develop a consciousness meter

One day in 2007, Dr Giulio Tononi lay on a hospital stretcher as an anesthesiologist prepared him for surgery. For Tononi, it was a moment of intellectual exhilaration. He is a distinguished chair in consciousness science at the University of Wisconsin, and for much of his life he has been developing a theory of consciousness. Lying in the hospital, Tononi finally had a chance to become his own experiment.

The anesthesiologist was preparing to give Tononi one drug to render him unconscious and another one to block muscle movements. Tononi suggested the anesthesiologist first tie a band around his arm to keep out the muscle-blocking drug. The anesthesiologist could then ask Tononi to lift his finger from time to time, so they could mark the moment he lost awareness.

The anesthesiologist did not share Tononi’s excitement. “He could not have been less interested,” Tononi recalled. “He just said, ‘Yes, yes, yes,’ and put me to sleep. He was thinking, ‘This guy must be out of his mind.”’

Tononi was not offended. Consciousness has long been the province of philosophers, and most doctors steer clear of their abstract speculations. After all, debating the finer points of what it is like to be a brain floating in a vat does not tell you how much anesthetic to give a patient.

But Tononi’s theory is, potentially, very different. He and his colleagues are translating the poetry of our conscious experiences into the precise language of mathematics. To do so, they are adapting information theory, a branch of science originally applied to computers and telecommunications. If Tononi is right, he and his colleagues may be able to build a ‘consciousness meter’ that doctors can use to measure consciousness as easily as they measure blood pressure and body temperature. Perhaps then his anesthesiologist will become interested.

“I love his ideas,” said Christof Koch, an expert on consciousness at the California Institute of Technology. “It’s the only really promising fundamental theory of consciousness.”

Tononi’s obsession with consciousness started in his teens. He was initially interested in ethics, but he decided that questions of personal responsibility depended on our consciousness of our own actions. So he would have to figure out consciousness first. “I’ve been stuck with this thing for most of my life,” he said.

Eventually he decided to study consciousness by becoming a psychiatrist. An early encounter with a patient in a vegetative state convinced Tononi that understanding consciousness was not just a matter of philosophy.

“There are very practical things involved,” Tononi said. “Are these patients feeling pain or not? You look at science, and basically science is telling you nothing.”

Tononi began developing models of the brain and became an expert on one form of altered consciousness we all experience: sleep. In 2000, he and his colleagues found that Drosophila flies go through cycles of sleeping and waking. By studying mutant flies, Tononi and other researchers have discovered genes that may be important in sleep disorders.

For Tononi, sleep is a daily reminder of how mysterious consciousness is. Each night we lose it, and each morning it comes back. In recent decades, neuroscientists have built models that describe how consciousness emerges from the brain. Some researchers have proposed that consciousness is caused by the synchronisation of neurons across the brain. That harmony allows the brain to bring together different perceptions into a single conscious experience.

Tononi sees serious problems in these models. When people lose consciousness from epileptic seizures, for instance, their brain waves become more synchronised. If synchronisation were the key to consciousness, you would expect the seizures to make people hyperconscious instead of unconscious, he said.


Consciousness is not simply about quantity of information, he says. Simply combining a lot of photodiodes is not enough to create human consciousness. In our brains, neurons talk to one another, merging information into a unified whole. A grid made up of a million photodiodes in a camera can take a picture, but the information in each diode is independent from all the others. You could cut the grid into two pieces and they would still take the same picture.

Consciousness, Tononi says, is nothing more than integrated information. Information theorists measure the amount of information in a computer file or a cell phone call in bits, and Tononi argues that we could, in theory, measure consciousness in bits as well. When we are wide awake, our consciousness contains more bits than when we are asleep.
For the past decade, Tononi and his colleagues have been expanding traditional information theory in order to analyse integrated information. It is possible, they have shown, to calculate how much integrated information there is in a network. Tononi has dubbed this quantity phi, and he has studied  it in simple networks made up of just a few interconnected parts. How the parts of a network are wired together has a big effect on phi. If a network is made up of isolated parts, phi is low, because the parts cannot share information.

Tononi argues that his Integrated Information Theory sidesteps a lot of the problems that previous models of consciousness have faced. It neatly explains, for example, why epileptic seizures cause unconsciousness. A seizure forces many neurons to turn on and off together. Their synchrony reduces the number of possible states the brain can be in, lowering its phi.

Tononi is also testing his theory in other ways. In a study published this year, he and his colleagues placed a small magnetic coil on the heads of volunteers. The coil delivered a pulse of magnetism lasting one-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, making them fire as well.

To track these reverberations, Tononi and his colleagues recorded brain activity with a mesh of scalp electrodes. They found that the brain reverberated like a ringing bell, with neurons firing in a complex pattern across large areas of the brain for 295 milliseconds.
Then the scientists gave the subjects a sedative called midazolam and delivered another pulse. In the anesthetised brain, the reverberations produced a much simpler response in a much smaller region, lasting just 110 milliseconds. As the midazolam started to wear off, the pulses began to produce richer, longer echoes.

In ‘Cognitive Neuroscience’, he and his colleagues reported that dreaming brains respond more like wakeful ones. Tononi is now collaborating with Dr Steven Laureys of the University of Liege in Belgium to test his theory on people in persistent vegetative states. Although he and his colleagues have tested only a small group of subjects, the results are so far falling in line with previous experiments.

If Tononi and his colleagues can get reliable results from such experiments, it will mean more than just support for his theory. It could also lead to a new way to measure consciousness. “That would give us a consciousness index,” Laureys said.

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