What Is the Fundamental Nature of Consciousness? [Excerpt]

Neuroscientist Giulio Tononi's PHI: A Voyage from the Brain to the Soul takes the reader on an imaginative tour in which Galileo tries to discover an explanation for our conscious selves

Pantheon Books

This chapter from PHI: A Voyage from the Brain to the Soul, by Giulio Tononi (Pantheon, 2012) describes Tononi’s theory of consciousness as a measure of information. The brain, Tononi postulates, consists of billions of neurons: think of them as if they were transistorlike bits that, when tallied, sum to equal more than their parts. That increment above and beyond—Tononi calls it phi—represents the degree to which any being, whether human or mule, remains conscious.

From the forthcoming book PHI: A Voyage from the Brain to the Soul, by Giulio Tononi

Copyright © 2012 by Giulio Tononi


Integrated Information: The Many and the One

In which is shown that consciousness lives where information is integrated  by a single entity above and beyond its parts

 When is an entity one entity? How can multiple elements be a single  thing? A question simple enough— but one, thought Galileo, that  had not yet been answered. Or perhaps, it had not been asked. 

The sensor of the digital camera certainly had a large repertoire of  states— it could take any possible picture. But was it a single entity?  You use the camera as a single entity, you grasp it with your hands as  one. You watch the photograph as a single entity. But that is within  your own consciousness. If it were not for you, the observer, would it  still be a single entity? And what exactly would that mean? 

While musing such matters, Galileo was startled by a voice. J., a man  with the forehead of an ancient god, addressed him in a polished tone:  “Take a sentence of a dozen words, and take twelve men, and tell to  each one word. Then stand the men in a row or jam them in a bunch, and let each think of his word as intently as he will; nowhere will there  be a consciousness of the whole sentence. Or take a word of a dozen letters,  and let each man think of his letter as intently as he will; nowhere  will there be a consciousness of the whole word,” J. said. 

Or take a picture of one million dots, and take one million photodiodes,  and show each photodiode its own dot. Then stand the photodiodes  well ordered on a square array, and let each tell light from  dark for its own dot, as precisely as it will; nowhere will there be a  consciousness of the whole picture, said Galileo.  “So you see that, Galileo,” J. continued. “There is no such thing as  the spirit of the age, the sentiment of the people, or public opinion.  The private minds do not agglomerate into a higher compound mind.  They say the whole is more than the sum of its parts; they say, but  how can it be so?” 

An image came to Galileo. An astronomer was watching the  sky in Padua, during an eclipse, and precisely at the same moment,  another astronomer was watching the night sky at the antipodes.  Would there be a single consciousness contemplating, in one great  image, the entire dome of the sky, the austral and boreal skies joined  seamlessly at the horizon? A single image of the entire sky, experienced  within one consciousness? That was absurd, thought Galileo,  and its absurdity had nothing to do with the distance between  the scientists. Whether the two were separated by the diameter of  the earth, or by a fraction of an inch, like two photodiodes on the  camera sensor, made no difference. Because in both cases, the two  parties could not interact. And if they could not interact, they could  not form a single entity, and they could not have a single, unified  conscious experience. 

 “Of course,” agreed J. “A blind man and a deaf man cannot compare  sounds and colors. One hears them and the other one sees them,  but could they compare them if they are together? Not even if they  were to live in the same house forever, not if they were conjoined  twins.” Like Ishma and El, thought Galileo. 

 “Nice words,” said Alturi, standing next to Galileo. “But what’s  the point? We were arguing about the information in a camera, and  you saw that, if the camera is large enough, it can be as much or more  than the information generated by a brain. Which shows that information,  as S. was saying, has little to do with consciousness. Isn’t it so?” 

Galileo hesitated. If one measured information the way S. did,  a camera was better than a brain: the larger the repertoire of states  available to a system, the greater the reduction of uncertainty— the  greater the information generated by the particular state the system  was in. But was this the right way of measuring information?  He thought of what J. had said, of the scientists in the northern and  southern hemispheres, of Ishmael’s left and right hemispheres. So he  tried: 

It should make a difference if the information is generated by a  system that is one, rather than just a collection of parts. 

 “Quite possibly,” said Alturi. “And how would one show the difference?”  He smiled, as if he knew that Galileo could not provide an  answer. 

 “I wish I knew,” said J., as if he knew there could not be an answer.  Galileo paused, as if lacking for words, then turned to J., and asked: 

If, with an extraordinarily thin and sharp blade, old Occam’s razor,  say, one were to split in two the sensor of the camera, in such a way  that half a million photodiodes lie on one side, and the other half a  million on the other side, what would then happen to the image seen  by the camera? 

 “Nothing would happen, of course,” answered J. “The camera  would go on working just as well, taking full pictures, the pictures  could be sent over the air, stored and replayed at will, and no one  would notice any difference.” 

Galileo held up the camera, and took a picture, with the split  sensor, of what was now on the screen before them. It was an Italian  word, SONO, the word for “I am,” and SONO was seamlessly  displayed. 

Indeed, said Galileo to J. As long as the sensor is in place, nothing  will change, because every one of the million photodiodes will  go on reporting its own separate dot, unaware of what its peers are  seeing. 

But what if, with a thin and sharp blade, one were to split in two  a brain? Recall Ishmael’s brain, in the crypt of Prince Venosa, when  Salerno froze the connections between his two hemispheres. Would  nothing change, as with the camera?  You know it already, said Galileo without waiting for an answer.  Ishmael split into Ishma and El, and Ishma saw the lady, and El the  brute, but no one saw them both— there was no Ishmael who could  see the adultery, as long as the two hemispheres were split. But when  the hemispheres embraced again with warmth, there was Ishmael  again, and Ishmael saw the couple joined. 

You know the answer then: Ishma would see SO, the Italian word  for “I know,” El would see NO, the word for “no,” but there would  be no Ishmael who would see SONO, and say, “I am.” Unlike the  camera image, the blade would split the conscious image and consciousness  itself would be divided. 

J. and Alturi remained silent, so Galileo went on. But if the connections  between the hemispheres are warm, as they are in your own  brain, you can try as hard as you may wish to split your experience in  two, to see SO independently of NO, but you will not succeed. Just  as you will not succeed in seeing the shape of things without their  color, or their color without their shape— you will remain one J., one  experience, one consciousness. 

 “Impregnable logic,” said J. “One plus one equals two, but not  quite,” he added.  

One thing is certain, said Galileo: there is nothing it is like to be  the sensor of a camera— consciousness cannot live there, because the  sensor is not a single entity, though it may be rich with a million photodiodes.  Just like there is nothing it is like to be two scientists, one in  the northern and one in the southern hemisphere. Nothing it is like to  be a row of twelve men, each thinking of a different letter. 

 “I see it,” said J. “The camera may be large, but is less than poor in  consciousness: it owns none and lacks existence in the realm of experience.  Compared to it, even a photodiode is richer, it owns a wisp of  consciousness, the dimmest of experiences, one bit, because each of  its states is one of two, not one of trillions. Yet being a photodiode is  more than not being at all. I wonder,” J. went on. “What if one splits  the brain into a million parts? First left and right, than front and back  into four quarters, then with a hundred other cuts through its white  matter, into a million separate grains, as separate as the grains on a  cob, or the photodiodes on the camera sensor: Would consciousness  disintegrate?” 

 “Never mind,” said Alturi. “Galileo hasn’t shown a difference in  number. If consciousness lives on information, one must squeeze  money out of a formula, the formula of S.” 

Allow me, said Galileo at once, without raising his eyes. If we cut  the camera sensor into its one million parts, the array of photodiodes,  how much information is generated by each photodiode? 

 “One bit, of course,” answered Alturi. “That’s what the formula  of S. tells us.” 

Now, said Galileo, how much information is generated by the  camera sensor? 

 “What a question,” said Alturi. “Being constituted of a million  photodiodes, it will generate one million bits.” 

ll right, said Galileo. How much information is generated by the  camera sensor above and beyond its parts? Beyond its one million  photodiodes, I mean. 

 “Zero, of course,” said Alturi after a while, not expecting he  would be questioned this way.  Precisely, said Galileo, feeling he was usurping Alturi’s role. The  camera does not generate any more information than the sum of its  parts. Therefore, at least with respect to information, we have no need  to invoke the camera above its parts. We might as well drop it from  the catalog of useful entities, cut it with Occam’s razor, and stick with  a million photodiodes. Entia non sunt multiplicanda praeter necessitatem. 

 “That’s just a matter of perspective,” intervened Alturi, who  seemed busy tipping the smoldering tobacco in his pipe onto the  floor. “You like to talk of photodiodes and ban the camera, I may  prefer the camera and spurn the photodiodes.” 

Not so, not so, hurried Galileo, think of Ishmael. He would  have seen SONO and understood “I am.” But after the connections  between his two brains were frozen, and Ishmael had disappeared,  nobody would be left who could see and understand SONO, “I am.”  Ishma and El together could never make up for it, for one saw SO and  understood “I know,” the other saw NO and understood “No.” In  this case, unlike with the camera, the whole is more than the sum of  its parts and cannot be reduced to them; Ishmael is more than Ishma  and El, and SONO cannot be reduced to SO and NO. 

 “I think I see the point,” said J. “The information generated by the  whole above and beyond its parts— call it integrated information— is  what distinguishes Ishmael from a camera. Does this seem right,  Alturi?” 

 “What would be right?” exclaimed Alturi, who was busy grounding  the tobacco out with his heel. “Is it right that a distribution of  system states, if it cannot be factorized into a product of distributions  of its parts, is not reducible? Of course, but SO what? What’s special  about this? There are all kind of things that cannot be factorized, that  cannot split without a loss, but why would any of this matter for  consciousness? Besides, there are many ways to divide a system into  parts, of factorizing distributions, and you will get a different answer  depending how you cut it into pieces.” 

 “True,” said J. “If integrated information has something to do  with consciousness, it should not change depending how you divide  a system into parts. Isn’t it so, Galileo?” 

The crucial cut, said Galileo, is the minimum cut, the cruelest cut  of all— the cut through a system’s weakest link, the cut that divides it  into its strongest parts— those that generate as much information as  possible by themselves, leaving as little as possible for the whole. 

 “Excellent,” said J. “Integrated information is the information  generated by a system above its parts, where the parts are those that,  taken independently, generate the most information. Now that we  have a definition, we need a symbol for it.” 

 “If you need a symbol, it should be Φ,” said Alturi. “That is the  symbol of the golden ratio— the right way of dividing something  into parts. And the minimum cut, which reveals how much information  is integrated information, is the right way of dividing a system  into parts, is it not? You should call it Φ.” 

That would be interesting, said Galileo. After all, the golden ratio  was studied by a fellow Pisan, the good old Φibonacci. 

 “It is better than that,” said J. “Φ is like Φenomenology, like experience,  which is what consciousness is.” 

Better than that, said Galileo. Φ has an I, for information, and an  O, a circle, for integration. Let’s call it Φ, then. 

 “Splendid,” said Alturi. “Now that you have your quantity and  your symbol, let’s see what follows. Clearly, every time some elements  interact, you’ll have some integrated information: a whole  that does not reduce to its parts. Then, if integrated information has  something to do with consciousness, as you seem to think, what follows  is quite simple: it follows that consciousness is like an onion. 

 “Take me and the neurons in my brain. Somewhere inside my  brain there is me, of course, but I am not alone. If you peel me away,  neuron by neuron, you’ll find other me, millions of me, each lacking  some part, but all conscious to some extent. I am just the most conscious  of my many me, but those diminished selves would be right in  claiming their own rights, except that I don’t hear them, but they are  along for the ride.  “

Then take my body. No doubt my body, too, is made of interacting  parts, a whole that cannot be reduced to its parts— either physically  or informationally— in fact the brain itself is just one of those  parts. So the body, too, is yet another consciousness, an even larger  onion than I thought I was. Its Φ may be much less than mine— its  minimum cut quite weak, say across my neck— but it, too, is carrying  on its own limited existence. A multiplication of selves, a proliferation,  of which I know nothing at all, and they know nothing of me. 

 “But it does not stop there. Then there is the two of us talking,  nay, the three of us, interacting as a whole that cannot be reduced  merely to the three of us taken independently. A Holy Trinity thinking  its little Trinitarian thoughts. 

 “And then a city, a country, or the entire world, all layers of the  universal onion, and each of them conscious, some more and some  less.” 

 “I see your point,” said J. “And yet consciousness seems to reside  just once inside my head, your head, and Galileo’s head. Then Φ cannot  be the answer.” 

The onion, too, must be peeled with Occam’s razor, said Galileo.  And when you do so, that will leave only its core— the core where  integrated information reaches its maximum— the core that holds  together while the rest peels off. 

 “So consciousness is not an onion, it is an onion’s core! This is quite  some progress,” said Alturi. “But if you and I talk, what then? Don’t  you and I, talking as we are doing now, form a larger core?” 

Occam’s razor, once again, answered Galileo. You just said: “You  and I, talking.” “You and I, talking” is much simpler, physically or  informationally, than a would- be chimera mingling you and I. That  monster has no holding power and would break down at its seams,  you and me, where reality is carved into individual entities. Think  not of monsters but of raindrops. Inside a drop of rain, molecules  interact more strongly than with the air outside, and so a surface  forms. The drop is a single entity and is contained within a border.  When two droplets meet, either they bounce and remain separate,  or they fuse and become a single, larger drop. There are no overlaps,  nor drops within other drops. So it may be with consciousness: consciousness  lives within a system where integrated information reaches  a maximum, inside its own drop. 

 “So what you have understood is this,” said Alturi: “Experience  cannot be reduced to anything less then it is. Impressive indeed.” 

Ignoring Alturi, J. turned to Galileo. “If you are right, we should  have a name for a system for which the information generated by the  whole above its parts reaches a maximum, the onion core, the raindrop  of consciousness. A complex, perhaps?” 

Let’s call it so, said Galileo— a complex. 

 “So a complex is where consciousness lives,” said J. “There consciousness  raises its house, erects its walls, and you are what’s inside,  the rest of the world is what’s outside. The house of consciousness is  one and cannot be shared: there is only one, only one owner, and it  excludes all others.” 

It was not clear whether Alturi liked this, but then he said: “I guess  when you apply this analysis to the sensor of the camera, it will break  down into complexes that are individual photodiodes, each of them  distinguishing between just two states, on or off, but there will be  no integrated entity— a complex— corresponding to the sensor. But  when you analyze your brain, you will find inside it a set of nerve  cells that form a large complex: one that can distinguish among a  large repertoire of states in a way that its parts cannot; and one that  does so maximally, more than any other set of nerve cells, more than  the entire body, than any crowd of men, than the world itself.” 

Precisely, said Galileo. 

 “Then I have something for you,” said Alturi, and handed Galileo  some notes. The notes were from Frick and were full of diagrams  representing parts of the brain. There was the cerebrum: without it,  Copernicus had lost his consciousness forever. Galileo remembered  when he and Frick had compared the cortex and thalamus to a great  city. The diagram showed that a large expanse of the cerebral system  formed a single complex of high Φ. This was because its elements,  different groups of neurons, were specialized for different functions,  and yet these specialists talked to each other— they were integrated  within a single great complex that could distinguish among a vast  number of different states, one for each experience. 

There was the cerebellum, which had even more elements, but  they were separated into many small modules that did not talk to each  other. Each of them formed a small, separate complex, and for each  little complex Φ was low. Like a collection of photodiodes, thought  Galileo, and remembered Poussin: the painter’s hand trembled without  a cerebellum, but his mind was rich and full. 

Then there were diagrams explaining why your eyes may be  blind but your consciousness can have inner vision, like the blind  painter in front of his great allegory. They showed how the visual  inputs reached the cerebral cortex, influenced its functioning, but  did not become part of the great complex of high Φ that gave rise to  consciousness. 

And there was his friend M., too, showing that all the nerves reaching  out of the great complex, though necessary to speak and act, did  not participate in it and thus did not contribute to his consciousness.  There were Galileo’s muses, the poetess and the gamba player, with  loops going out and into the great complex, but the loops themselves  remained outside. This was why, thought Galileo, so many neural  processes that make us understand speech, or find the right words,  or say them, or remember them, perform marvelous feats, but still  remain outside the special sphere of consciousness. 

And finally there was Ishmael, with the nerve fibers linking the  right and left hemisphere split, and the great complex splitting in two  and yielding two consciousnesses with similar values of Φ, Ishma and  El. Other, smaller splits, might explain why Teresa could see and yet  did not know it, thought Galileo. And surely Φ was low during the  frenzy of seizures, or the deep waves of unconscious sleep, because  the repertoire of distinguishable brain states was bound to shrink. 

 “You think this might explain it?” asked J. after a while. 

Consciousness is such a lofty bird that it must be caught with an  equation, said Galileo. First catch the concept, then dress it in the language  of mathematics. Then, and only then, knowing how it can be  measured, would one truly know what it is. It may be, said Galileo,  it may be that the essence of consciousness is integrated information. 

And this may be a way this concept can be grasped— a way to catch  this bird: a way to find what entity is a single entity, a nucleus of  experience. 

 “Something still perplexes me,” J. said pensively. “The brain is  inconceivably complex, so much so that trying to understand its  mysteries through a network of equations is like trying to collect the  sea with fishing nets. The brain has more trees than the jungle, more  streets than a great city, is more plastic than the desert’s sand, more  changeable than the waves of the sea. And who would hope to reduce  the endless wavering of the dunes, the bustling traffic of the market,  the tangle of leaves and animals in the jungle canopy, to a series of  equations, or worse, to a set of numbers? Mathematicians may weave  their networks, but in the end, I am afraid, they will catch nothing.” 

 “Do not be afraid, since there is beauty in principles,” said Alturi’s  voice from a distance, and J. turned to question Galileo. 

But Galileo too was far away. For he had read something at the end  of Frick’s notes, something he recognized from long before:  

Philosophy is written in this grand book— the universe I say— that is  wide open in front of our eyes. But the book cannot be understood unless  we first learn to understand the language, and know the characters, in  which it is written. It is written in the language of mathematics, and  its characters are triangles, circles, and other geometric figures, without  which it is humanly impossible to understand a single word of it; without  these it is like wandering in vain in an obscure labyrinth. 

So Galileo felt, for the first time in a long time, that he must write  what he had learned. And this is what he wrote:

 Integrated information measures how much can be distinguished by the  whole above and beyond its parts, and Φ is its symbol. A complex is  where Φ reaches its maximum, and therein lives one consciousness— a  single entity of experience.

Notes  “The whole is more than the sum of its parts” is an expression that  comes from Aristotle’s Metaphysics, which Galileo knew well. William  James thought that integration was a key to consciousness and  fought hard to understand it, as revealed by some excerpts from his  Principles of Psychology integrated into this chapter. Unfortunately he  never succeeded and eventually gave up amid doubts and denial,  writing an essay with the revealing title “Does Consciousness Exist?”  James’s photograph is from the Houghton Library, Harvard University.  The all-sky night photograph of the Northern Galactic Hemisphere  (on the left) was taken by Tunç Tezel at the Canary Islands; the  Southern Galactic hemisphere (on the right) was taken by Stéphane  Guisard in the Acatama Desert. The picture obtained by joining the  horizons of the two all- sky images was the Astronomy Picture of  the Day on July 30, 2011 (A Tale of Two Hemispheres).  If integrated information, measured by Φ (the Greek letter phi),  is indeed the weighty concept at the heart of consciousness that it is  claimed to be, this chapter introduces it in a rather light- weighted  manner. Perhaps the author was trying to avoid equations at all costs,  but the result is far from satisfactory. Versions of Φ dressed in equations,  but in the end just as unsatisfactory, are found in Tononi and  Sporns, BMC Neuroscience (2003); Tononi, BMC Neuroscience (2004);  Biological Bulletin (2008); Balduzzi and Tononi, PLoS Computational  Biology (2008); Tononi, Archives italiennes de biologie (2010, 2011). Information  was defined as “a difference that makes a difference” by  Gregory Bateson, in Steps to an Ecology of Mind (University of Chicago  Press, 1972). The Ripe Harvest by Klee is at the Sprengel Museum,  Hanover, Germany. The last portrait is by Arcimboldo (disliked by  Galileo and modified in bad taste, if not bad faith) and is known as  Adam (Eve’s counterpart, private collection).

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