Take a theory of consciousness that calculates how aware any information-processing network is聽鈥� be it a computer or a brain. Trouble is, it takes a supercomputer billions of years to verify its predictions. Add a maverick cosmologist, and what do you get? A way to make the theory useful within our lifetime.
Read more: What is consciousness?
How your brain creates the feeling of being is the biggest problem in neuroscience. But we are coming closer to cracking it
Integrated information theory (IIT) is one of our best descriptions of consciousness. Developed by neuroscientist of the University of Wisconsin at Madison, it鈥檚 based on the observation that each moment of聽awareness is unified. When you contemplate a bunch of flowers, say, it鈥檚 impossible to be conscious of the flower鈥檚 colour independently of its fragrance because the brain has integrated the sensory data. Tononi argues that for a system to be conscious, it must integrate information in聽such a way that the whole contains more information than聽the sum of its parts.
The measure of how a system integrates information is called phi. One way of calculating phi involves dividing a system into two and calculating how dependent each part is on the other. One cut would be the 鈥渃ruellest鈥�, creating two parts that are the least dependent on each other. If the parts of the cruellest cut are completely independent, then phi is zero, and the system is not conscious. The greater their dependency, the greater the value of phi and the greater the degree of consciousness of the system.
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The cruellest cut
Finding the cruellest cut, however, is almost impossible for聽any large network. For the human brain, with its 100聽billion neurons, calculating phi like this聽would take 鈥渓onger than the聽age of our universe鈥�, says , a cosmologist at聽the Massachusetts Institute of聽Technology.
Tegmark has come up with a fast way of approximating phi. He聽treats each neuron in the network as a node and their interconnections as links. He assigns a thickness to each link, proportional to the strength of the interconnection. Now, imagine turning a knob so that聽the thinnest links fade out. The picture will look somewhat different. Try again, fading out the聽next-thinnest links. Continue until the single interconnected web breaks into two. Tegmark has聽shown that this configuration approximates the cruellest cut.
Just a second
Crucially, this dramatically cuts down the time it takes to find phi. 鈥淚t goes from being above the age of the universe to something quite manageable,鈥� says Tegmark聽鈥� he estimates it would take less than a second for a human brain.
鈥淚t鈥檚 cool stuff,鈥� says Christof Koch of the Allen Institute for Brain Science in Seattle. 鈥淚t鈥檚 essential if we are ever to measure phi for real systems and not just toy models with 10 or 20 binary neurons.鈥�
The reduced computation time聽means we should be able to test the theory. This can be done using things like fMRI scans to map the neural interconnections of people in varying states of consciousness聽鈥� people in a coma, in dreamless sleep or looking at a bunch of flowers, for example. Applying Tegmark鈥檚 model to approximate phi in each case, we聽should find that it scales with the person鈥檚 level of awareness.
Two halves of the whole
The theory could also be tested聽in people whose brain hemispheres have been surgically separated as a treatment for epilepsy. of聽the聽University of California, Santa聽Barbara, has discussed with Tononi the idea of measuring the phi of each half of聽the brain. His work shows that each hemisphere retains its own consciousness and is unaware of the other half. IIT predicts that the phi for each individual hemisphere should be less than the phi for the unseparated brain. 鈥淭he idea of making the measurement easier is very appealing,鈥� says Gazzaniga.
Once IIT is verified, phi could be used to identify people with consciousness disorders who have been misdiagnosed. For example, someone who is conscious but completely paralysed may be diagnosed as being in a minimally conscious state. Their high phi value would alert doctors to the mistake. , a neurologist at the University of Liege in Belgium has worked with Tononi to find ways of calculating phi for his patients. He is excited that Tegmark is on board to share a physicist鈥檚 perspective on the project. 鈥淭his is wonderful, this is what we need,鈥� he says. 鈥淭his is the problem for science鈥�the origin of the universe and matter and how we are conscious in that universe.鈥�
But Laureys cautions that IIT is a long way from solving the so-called hard problem of consciousness: explaining how the neural activity of a material brain gives rise to seemingly immaterial mental life. 鈥淭ruly, nobody at present understands how we go from matter to mind,鈥� he says.
Journal reference: pre-print,
