My mind’s abuzz with anticipation, because I’m heading to Tucson, Arizona, for “The Science of Consciousness,” the famous biannual exploration/celebration of the murkiest of all mysteries. I’m attending as both reporter and speaker. I cajoled organizer Stuart Hameroff into letting me give a talk on “The Quest to Solve Consciousness: A Skeptic's View.” As the abstract says, I’ll “assess major ongoing approaches to consciousness. Do they represent genuine progress, or do they corroborate the mysterian position that the hard problem is intractable?” I attended the first Tucson conference in 1994 and reported on it in Scientific American and in “The Consciousness Conundrum,” a chapter in my 1999 book The Undiscovered Mind. Here is an abridged version of that chapter. After skimming this, browse “Further Reading” (especially my post on integrated information theory) and draw your own conclusions about how far mind-science has progressed--or regressed--over the last 22 years. -–John Horgan

Like all science writers, I often receive letters from people who claim to have discovered something extremely important: a theory that proves Einstein's view of time and space was wrong, a three-page proof of Fermat's last theorem, or simply the key to everything. The writers are generally unaffiliated with any formal institution (prisons and mental hospitals don't count) and desperate for recognition. Some missives are obviously products of clinical derangement, but others are quite lucid. The authors construct their arguments carefully and minimize references to God or Einstein, but something is still a

Although I rarely respond, I’m haunted by these lonely truth-seekers seeking validation from the cold-hearted world. I sometimes wish I could put each person who has discovered the key to everything in touch with all the others who have found a different key. Ideally, they could have a conference, exchange views and agree—or, more likely, not--on whose key worked best.

Such a conference would resemble "Toward a Scientific Basis of Consciousness." Held in Tucson, Arizona, in April 1994, the meeting was a microcosm of the entire enterprise of mind-related science, with all its fractiousness and confusion amplified a thousand-fold. Virtually every scientific discipline and not a few pseudo-scientific ones were represented in Tucson. Many speakers hailed from eminent institutions, and their lectures had all the trappings of serious scientific discourse: technical terms, references to experimental data, equations. But they still seemed a

The tone was established early on by the meeting’s chief organizer, Stuart Hameroff, an anesthesiologist at the University of Arizona and quantum-consciousness proponent. Looking out over the motley crowd during his welcoming speech, Hameroff, sporting a goatee and ponytail, exclaimed, "Wow, this is just like Woodstock!"

Many speakers highlighted the exotic dimensions of consciousness. Andrew Weil, the alternative-medicine guru, described smoking the dried venom of toad with a friend, with whom he shared the same hallucinations. He and his friend, Weil said, were "in each other's consciousness." Science could not claim to comprehend consciousness, Weil asserted, unless it explained such mystical experiences.

Danah Zohar, trained in physics, philosophy and religion, reiterated the main theme of her 1990 book The Quantum Self. It is time to move beyond dualism, she said, and accept that matter and mind both stem from "the quantum." Human thoughts, she assured us, are quantum fluctuations of the vacuum energy of the universe, which "is really God."

Those who found the formal lectures too bland could forage in the halls for more far-fetched ideas. I met a large, bald man, clad in white pajamas, who was frustrated that most speakers defined consciousness so narrowly. Consciousness is obviously a property not just of humans and other higher animals but of all natural phenomena, including plants and rocks.

I replied that scientists would not get very far in understanding consciousness if they defined it in such a flexible manner. The pajama man told me that he, like me, used to be stuck in an extremely materialistic paradigm. He had grown out of it, and I might too, if I wasn't so close-minded.

Koch’s Oscillations

If one had to seed the contenders within this scientific free-for-all, the number-one position would probably go to Christof Koch, a German-born neuroscientist. He deserves much of the credit--or blame--for the surging scientific interest in consciousness.

In 1990 Koch and Francis Crick, co-discoverer of the double helix, proclaimed that it was time to make consciousness a subject of empirical investigation. By finding the neural activity correlated with consciousness, Crick and Koch argued, scientists could construct rigorous scientific models, analogous to those that explain heredity in terms of DNA. Crick elaborated on these ideas in his 1994 book The Astonishing Hypothesis. Crick dedicated the book to Koch, "without whose energy and enthusiasm this book would never have been written."

Koch's energy and enthusiasm were evident in his lecture in Tucson. A tall, lean man with a staccato, German-accented patter, he prowled the stage as he spoke, pausing only to flash a new slide or crack a joke. He defined consciousness as the ability to pay attention to one subset of all the stimuli constantly impinging on the mind.

Koch elaborated on a proposal by him and Crick that the oscillation of many neurons at the same frequency--40 hertz per second—might be the key to attention. Such oscillations could “bind together” the neural activity underpinning our recognition of, say, a friend’s face at a party. He acknowledged that the evidence linking 40-hertz oscillations to awareness is tenuous; it has shown up most clearly in anesthetized cats.

Walter Freeman, a tall, thin, white-bearded neuroscientist, advocated a more complex model of awareness based on chaos theory. Brains, he asserts, are chaotic systems, which by definition are extremely sensitive to minute influences. This fact accounts for the brain's ability to respond to complex perceptual data with astonishing rapidity. But even Freeman conceded that his theory is only--at best--one piece of the puzzle.

Chalmers’s Information Theory

David Chalmers, an Australian philosopher, rejected the neural approach of both Koch and Freeman. Physiological theories can at best describe only functions--such as attention, memory, intention, introspection--correlating to specific processes in the brain. But neurological theories cannot explain why the performance of these functions is accompanied by conscious experience, which Chalmers called "the hard problem."

Up to this point, Chalmers sounded like a mysterian, a term coined by philosopher Owen Flanagan to describe those who doubt consciousness can be solved. But Chalmers thinks he might have found a solution to the hard problem. Just as physics assumes the existence of such fundamental properties of nature as space, time, energy and mass, perhaps a theory of consciousness must posit the existence of a new fundamental property: information.

Information, Chalmers explained, always has some physical embodiment, such as the arrangement of ink spots on a piece of paper or of electrons in a computer. But information is not purely physical; it also has a "phenomenal," or subjective, aspect.

Chalmers noted that according to his theory, any object that processes information must have conscious experience. "A mouse has a simpler information processing structure than a human, and has correspondingly simpler experience; perhaps a thermostat, a maximally simple information processing structure, might have a maximally simple experience?"

In later writings, Chalmers boldly answered this question in the affirmative: If one accepts his information-based hypothesis, one must accept that a thermostat is conscious. In effect, Chalmers was espousing a philosophy like that of the bald-headed man in pajamas who harangued me in the hallway: everything is conscious.

Koch ridiculed Chalmers’s information idea, complaining, “Why don’t you just say that when you have a brain the Holy Ghost comes down and makes you conscious?” Chalmers's talk was nonetheless a great success. People clustered around him after his session and for the rest of the meeting, telling him how much they admired his ideas.

The Quantum Mind of Penrose

One of the few Tucson speakers who sparked as much excitement as Chalmers was mathematical physicist Roger Penrose. Godel's theorem, Penrose said, implies that mathematics can never be reduced to an algorithm or set of rules that churns out theorems and proofs. Penrose said his own mathematical work arose not from any deductive, logical process but from sudden intuitions and insights into an indescribably beautiful Platonic realm.

Penrose concluded that no mechanical, ruled-based system--that is, neither classical physics, computer science nor neuroscience as presently construed--can account for the mind's creative capacity. That requires "a new physical theory" incorporating nonlocal quantum effects. Nonlocal effects, which Einstein described as “spooky action at a distance,” might come into play at the level of microtubules, minute tunnels of protein that serve as a kind of cellular skeleton.

Penrose's reference to microtubules delighted Stuart Hameroff, the anesthesiologist who organized the Tucson meeting. It was Hameroff who first proposed that microtubules might be the seat of consciousness.

Other proponents of quantum consciousness abounded in Tucson, but so did critics. Koch summed up the quantum-consciousness thesis in a syllogism: Quantum mechanics is mysterious, and consciousness is mysterious, therefore they must be related. Other skeptics pointed out that nonlocality is generally observed only at temperatures far below the temperature of living brains.

The Solipsism Problem

Not all speculations about consciousness are equally distant from the truth. For example, we should reject any theory or metaphysics that places mind and matter on an equal footing or even gives primacy to mind. To put it bluntly, bodies without minds are common, but only psychics and psychotics see minds without bodies.

The neural approach to consciousness advocated by Koch, Crick and others could one day be validated by experiments on humans and other animals. By studying blindsight, anesthesia and other phenomena, researchers could isolate neural events both necessary and sufficient for human consciousness. This knowledge might have practical consequences, such as helping artificial-intelligence researchers make machines more like us.

But a scientific explanation of human consciousness will almost surely not end our endless debates over consciousness, because it will leave too many questions unanswered. Example: What conditions are both necessary and sufficient for consciousness to occur not only in humans but in any collection of matter? Here we are bumping into the solipsism problem, the fact that no one really has access to anyone else's consciousness (and toad-juice hallucinations don't count).

If or when computers become capable of chatting with us like old friends, many of us might be inclined to grant them consciousness. But reasonable people can always disagree, because there is no way to settle the dispute empirically. As Koch blurted out to Chalmers when he floated his conscious-thermostat idea, "How do I even know you're conscious?"

Explanation Versus Revelation

Moreover, people arguing about whether consciousness can be explained invest not only the term consciousness with different meanings but also explanation. For some hard-nosed types, such as Koch, an explanation will and must take the form of a physiological--and, more precisely, neural--model.

Others, such as Chalmers and Penrose, suggest that any neural model will be insufficient; consciousness requires a much more profound explanation. They are looking for an explanation so powerful that it will dispel the mystery from consciousness, like the sun burning off a morning fog. They are seeking not an explanation but a revelation.

During his talk at Tucson, Koch conceded that a neural explanation of consciousness might not solve the mind-body problem to everyone's satisfaction. But such an outcome might simply be beyond the scope of science. Koch paraphrased a "giant of the twentieth century," Dirty Harry, the cinematic cop played by Clint Eastwood: "A scientist has gotta know his limitations."

Koch once wrote in Nature that when we “understand the entire cascade of events leading from light of a certain wavelength impinging on my retina to activation of neurons that correlate with my feelings of 'redness,' the 'hard' problem will have disappeared (by analogy to the disappearance of the problem of vitalism). Or we might simply have to accept the fact that the world is as it is and subjective feeling arises out of the physical world in a way that is not further amenable to reductionist, empirical science."

Artificial-intelligence enthusiasts have speculated that super-intelligent machines--or humans who have boosted their intelligence with brain implants and genetic engineering--might solve the mind-body problem. Others nurture the hope that even we ordinary humans can comprehend our minds through meditation, psychedelics and other mind-altering methods.

My own suspicion is that the more intelligent or enlightened we are, the more baffled we will be by consciousness--and life in general--regardless of the power of our scientific explanations.

Further Reading:

Meta-post: Horgan Posts on Brain and Mind Science

The Singularity and the Neural Code

Scott Aaronson Answers Every Ridiculously Big Question I Throw at Him