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(consciousness redux) A Theory of Consciousness Is complexity the secret to sentience, to a panpsychic view of consciousness? BY CHRISTOF KOCH DO YOU THINK that your newest ac­ en organism has subjective states, has versity of Wisconsin–Madison. Tononi quisition, a Roomba robotic vacuum feelings. has developed and refined what he calls cleaner that traces out its unpredictable The reason is that we lack a coherent the integrated information theory (IIT) paths on your living room floor, is con­ framework for consciousness. Although of consciousness. scious? What about that bee that hovers consciousness is the only way we know above your marmalade­covered break­ about the world within and around us— An Integrated Theory fast toast? Or the newborn who finally shades of the famous Cartesian deduc­ IIT is based on two axiomatic pillars. fell asleep after being suckled? Nobody tion cogito, ergo sum—there is no agree­ First, conscious states are highly dif­ except a dyed­in­the­wool nerd would ment about what it is, how it relates to ferentiated; they are informationally highly organized matter or what its role very rich. You can be conscious of an un­ in life is. This situation is scandalous! We countable number of things: you can have a detailed and very successful frame­ watch your son’s piano recital, for in­ work for matter and for energy but not stance; you can see the flowers in the for the mind­body problem. This dis­ garden outside or the Gauguin painting mal state of affairs might be about to on the wall. Think of all the frames from change, however. all the movies you have ever seen or that The universal lingua franca of have ever been filmed or that will be our age is information. We are used filmed! Each frame, each view, is a spe­ to the idea that stock and bond prices, cific conscious percept. books, photographs, movies, music Second, this information is highly in­ and our genetic makeup can all be tegrated. No matter how hard you try, turned into data streams of zeros and you cannot force yourself to see the ones. These bits are the elemental atoms world in black­and­white, nor can you Is iRobot’s Roomba robotic vacuum cleaner of information that are transmitted over see only the left half of your field of view conscious? How about a bee, a comatose ); patient or a sleeping baby? Integrated an Ethernet cable or via wireless, that and not the right. When you’re looking information theory might tell us. are stored, replayed, copied and assem­ bled into gigantic repositories of knowl­ Roomba ( edge. Information does not depend on think of the first as being sentient; ad­ the substrate. The same information can herents of Jainism, India’s oldest reli­ be represented as lines on paper, as elec­ gion, believe that bees—and indeed all trical charges inside a PC’s memory living creatures, small and large—are banks or as the strength of the synaptic aware, whereas most everyone would connections among nerve cells. accord the magical gift of consciousness Since the early days of computers, to the baby. scholars have argued that the subjective, The truth is that we really do not phenomenal states that make up the life Pictures Times/Redux York New know which of these organisms is or is of the mind are intimately linked to the not conscious. We have strong feelings information expressed at that time by ENICOLA about the matter, molded by tradition, the brain. Yet they have lacked the tools C ONY religion and law. But we have no objec­ to turn this hunch into a concrete and T tive, rational method, no step­by­step predictive theory. Enter psychiatrist and ); ) procedure, to determine whether a giv­ neuroscientist Giulio Tononi of the Uni­ Koch bee IMAMOGLU ( IMAMOGLU The truth is that we really do not know which of these OTOSTOCK ( F FATMA ( organisms is or is not conscious. ) AGE 16 SCIENTIFIC AMERICAN MIND July/August 2009 the family photographs on is, the more synergy it has, the more con­ my Macintosh are not scious it is. If individual brain regions linked to one another. The are too isolated from one another or are computer does not know interconnected at random, Φ will be that the girl in those pic­ low. If the organism has many neurons tures is my daughter as she and is richly endowed with specific con­ matures from a toddler to nections, Φ will be high—capturing the a lanky teenager and then quantity of consciousness but not the a graceful adult. To my quality of any one conscious experience. Mac, all information is (That value is generated by the informa­ equally meaningless, just a tional geometry that is associated with vast, random tapestry of Φ but won’t be discussed here.) zeros and ones. Yet I derive meaning Explaining Brain Facts from these images because The theory can account for a number my memories are heavily of puzzling observations. The cerebel­ at your friend’s face, you can’t fail to also cross­linked. And the more intercon­ lum, the “little brain” at the back of the notice if she is crying. Whatever infor­ nected, the more meaningful they be­ brain that contains more neurons than mation you are conscious of is wholly come. Indeed, Tononi’s IIT postulates the convoluted cerebral cortex that and completely presented to your mind; that the amount of integrated informa­ crowns the organ, has a regular, crystal­ it cannot be subdivided. Underlying this tion that an entity possesses corresponds linelike wiring arrangement. Thus, its unity of consciousness is a multitude of to its level of consciousness. circuit complexity as measured by Φ is To be conscious, you must be a single, integrated entity ( with a large repertoire of highly differentiated states. ) causal interactions among the relevant These ideas can be precisely ex­ parts of your brain. If areas of the brain pressed in the language of mathemat­ start to disconnect or become fragment­ ics using notions from information ed and balkanized, as occurs in deep theory such as entropy [see box on sleep or in anesthesia, consciousness next page]. Given a particular brain, fades and might cease altogether. Con­ with its neurons and axons, dendrites sider split­brain patients, whose corpus and synapses, one can, in principle, ) callosum—the 200 million wires linking accurately compute the extent to the two cortical hemispheres—has been which this brain is integrated. From cut to alleviate severe epileptic seizures. this calculation, the theory derives The surgery literally splits the person’s a single number, Φ (pronounced sleeping baby sleeping consciousness in two, with one con­ “fi”). Measured in bits,Φ denotes scious mind associated with the left the size of the conscious reper­ hemisphere and seeing the right half of toire associated with any net­ the visual field and the other mind aris­ work of causally interacting UPITERIMAGES ( J ing from the right hemisphere and seeing parts. Think of Φ as the ); the left half of the visual field. synergy of the system. To be conscious, then, you need to be The more integrat­ a single, integrated entity with a large ed the system repertoire of highly differentiat­ comatose man comatose ( ed states. Although the 60 ­giga­ byte hard disk on my MacBook exceeds in capacity my lifetime FOTOSTOCK of memories, that information AGE is not integrated. For example, www.SciAmMind.com SCIENTIFIC AMERICAN MIND 17 (consciousness redux) If you lose your cerebellum, you will never be a dancer or ( pianist, but your consciousness will be unimpaired. ) low as compared with that of the cere­ thalamic complex is well suited to be­ ment (REM) sleep. What is paradoxical bral cortex. Indeed, if you lose your cer­ have as a single dynamic entity endowed is that the average firing activity of indi­ ebellum you will never be a rock climb­ with a large number of discriminable vidual nerve cells does not differ that er, pianist or ballet dancer, but your states. Lose one chunk of a particular much in deep sleep and quiet wakeful­ consciousness will not be impaired. The cortical area, and you might be unable ness. At the whole system level, though, cortex and its gateway, the thalamus— to perceive motion. If a different area electroencephalographic electrodes on the quail egg–shaped structure in the were lesioned, you would be blind to the skull pick up slow, large and highly center of the brain—on the other hand, faces (yet could see the eyes, hair, mouth synchronized waves during deep sleep. are essential for consciousness, provid­ and ears). Because these waves are quite regular, ing it with its elaborate content. Its cir­ When people are woken from deep they will disrupt the transfer of specific cuitry conjoins functional specializa­ sleep, they typically recall experiencing information among brain cells. tion with functional integration thanks nothing or, at best, only some vague Every day, in tens of thousands of to extensive reciprocal connections bodily feeling; this experience contrasts surgical operations, patients’ conscious­ linking distinct cortical regions and the with the highly emotional narratives our ness is quickly, safely and transiently cortex with the thalamus. This cortico­ brains weave during rapid­eye­move­ turned off and on again with the help of How to Calculate Consciousness in All Creatures Integrated information theory uses mathematics (bottom) to quantify the amount of integrated information an entity possesses—and thus its level of consciousness. The challenge: we cannot yet calculate the state of awareness for even the simple roundworm (left) with current computers, let alone deal with the complexity of the human brain.

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