JOURNAL OF THE ROYAL SOCIETY OF MEDICINE Volume 93 November 2000 Medical constraints on the quantum mind Nick Lane PhD J R Soc Med 2000;93:571±575 Consciousness de®nes mankind. We each cherish a personal own experience. The paradox has led some to claim that interpretation of what, as our most private possession, our consciousness can only be veri®ed through its own existence own self, it might be. Our personal preferences carry over. and therefore cannot be a physical force. According to the Religious thinkers see consciousness as a direct line to God, mysteries of quantum mechanics, the world at large also philosophers as the crux of Cartesian dualism, linguists as needs an observer to make things real. SchroÈdinger's an attribute of the language instinct. Historically, most equation showed that the path of a wave-particle is biologists have preferred to ignore so vague a concept and indeterminate. The wave passes simultaneously through get on with answering questions with more tangible any conceivable, and no doubt many inconceivable, answers, abandoning the ®eld to the mathematicians and positions in space and time. The act of observation is physicistsÐwho lean towards a unifying explanation assumed to resolve this underlying state of quantum grounded in the fundamental laws of physics. A modern indeterminacy, bringing about a `collapse' of the wave vogue is to discuss consciousness in terms of macro- function and a measurable outcome. In other words, an quantum effects, and the greatest failing of this approach observer is necessary to precipitate an event 'curiosity killed has been to turn a blind eye to the constraints imposed by the cat). But even if we grant that consciousness and medicine. quantum mechanics both demand an observer, this seems a whimsical basis for asserting a fundamental link. REVIEW ARTICLES A more robust challenge to classical models of INVASION OF THE MIND SNATCHERS consciousness arises from some apparent oddities in our Why is consciousness so attractive to quantum physicists? stream of consciousness. Neurosurgical experiments by One reason stems from the impression that conventional Benjamin Libet and others indicate that sensory stimuli may molecular biology has failed to provide a physical basis for take up to half a second to register consciously, and that we consciousness, therefore it cannot be considered physical in then `refer' our awareness back in time to correspond to a classical sense. Put another way, since we do not 'yet) when the stimulus was actually applied1. We `think' it understand consciousness in terms of familiar biological happened before we became consciously aware of it. Daniel paradigms, we must look for something more outlandish. Dennett compares the process with that of visual referral, This is obviously a logical fallacy, but it is easy to succumb whereby we project our internal neuronal construct of our to the feeling that we are missing something. Compare the surroundings back into the external environment2. Thus, situation, for example, with that in embryology. We cannot just as we perceive that a tree is not inside our head, so we pretend to understand the full workings of fetal perceive stimuli without an obvious time-lag. Greater development, but no serious biologist would argue that dif®culties are presented in the conscious initiation of embryology is not ultimately intelligible in terms of gene events, which may take even longer. Time-lags as long as a expression. Not so with consciousness. Few neuroscientists second have been recorded between a conscious decision to would take a bet that consciousness will ®nally be explained ¯ex a ®nger, say, and the actual muscular contraction1. without reference to the fundamental properties of matter. Roger Penrose has argued that such delays are incompatible Unlike the physicists, however, most would at least like to with our sense of the world, and would prevent us from try. Why introduce a new and even more baf¯ing variable playing ping-pong or participating in a rapid verbal unless we really must? exchange3. Editing out time lapses in these cases cannot A deeper and more mysterious connection between be achieved by temporal referral, so Penrose proposes that consciousness and quantum physics lies in the paradox of virtually instantaneous quantum processes must underlie the observer. We have no way of measuring whether an ice conscious decision-making. But of course, nothing we do is cube feels sad as it melts; we just assume that because it is instantaneous. Our response times in ping-pong are inanimate and shows no sign of pain it does not. Similarly, compatible with more or less unconscious re¯exes; we we cannot impute consciousness to a computer, a dog, or are seldom consciously aware of sentence construction as even another human being, except through reference to our we speak; and mental lapses of a few seconds in conversation, while a new point `sinks in', are a University Department of Surgery, Royal Free and University College Medical frustratingly common experience. Any real need for School, Pond Street, London NW32QG, UK E-mail: [email protected] quantum processing seems to be missing. 571 JOURNAL OF THE ROYAL SOCIETY OF MEDICINE Volume 93 November 2000 IN TWO MINDS ABOUT THE BASICS ability of particles to cross solid barriers)4. Walker backs his theory by arguing that synaptic morphology corre- Although consciousness cannot be explained by waves of sponds closely to that predicted by quantum tunnelling gene expression 'which are far too slow to constitute calculations, based on the likelihood of post-synaptic changes in mood or awareness) there is no prima facie ®ring4. But this hardly proves the point. Something reason to suppose that the phenomenon cannot be similar is obviously required for conventional neurotrans- explained by a combination of classical neurochemistry mission. and massively parallel brain circuitry. This amounts to a Roger Penrose has put forward similar arguments to statement of faith. So too does the view that consciousness those of Walker, proposing that, rather than cytoplasmic can only be explained by reference to quantum mechanics. RNA, the microtubules provide the intracellular architec- I prefer the ®rst view, if only because I am a biologist; but ture required for quantum delocalization across neurons. can we begin to discriminate? I think we can. A quantum Penrose and Stuart Hameroff cite the accumulation of mechanical theory of consciousness demands some very anaesthetic agents within the microtubules as support for special properties of matterÐmacroquantum effects are their importance in sustaining consciousness3,5. Yet there is not to be found all around us, after allÐwhereas a classical little evidence that the action of anaesthetic agents is biological explanation demands an extraordinary organiza- related to their accumulation in the microtubules rather tion of rather ordinary matter. than, for example, their various effects on ion channel If we accept that consciousness is an emergent property function, calcium in¯ux, synaptic transmission or lipid of very complex nervous systems we can de®ne a few of bilayer integrity. Indeed, despite the long search for a the features that must be expressed for the system to unitary theory of anaesthesia, there is no reason to suppose generate consciousness. For a classical explanation, this is that all anaesthetic agents work in the same way. They conceptually simple: all we must do is show that an produce a spectrum of activity in the central nervous enormously complex parallel processing system, system, and different agents produce different patterns of comprising a hundred billion neuron-equivalents, coupled activity. Conversely, several agents known to affect the to a multifaceted and profoundly integrated sensory microtubules, such as colchicine 'used in the treatment of system, and an ability to remember and learn, is capable gout), have no measurable effect on consciousness. The of giving rise to consciousness. In other words, we have to microtubular theory smacks of a physics-orientated `theory prove that consciousness will emerge from a 'sophisticated) of everything' rather than a serious biological proposition. robot. That might take a while. Meanwhile, what features The most widely accepted quantum theory of mind was of the nervous system are needed to support a quantum proposed by Ian Marshall in 1989, who argued that mechanical theory of consciousness? And what happens consciousness might be a type of quantum coherence when these features break down? maintained by the so-called FroÈhlich effect6. Quantum coherence is a state of energy delocalization, in which large A MIXED OFFERING numbers of particles share a single quantum state, losing For a purportedly unifying theory, there is surprisingly their own individuality in the same way that, in an little unity about what might constitute the quantum orchestra, the individual violins merge into a single sound. mechanical mind. The overarching assumption is that Herbert FroÈhlich, one of the pioneers of superstate physics, consciousness is some type of macroquantum effect, but described a system in which the natural oscillation of under this umbrella there is little to choose between a proteins could produce a coherent state if metabolic energy number of possibilities. Macroquantum effects known to was supplied at a constant rate7. The metabolic energy is occur at temperatures above absolute zero include used to pump changes in protein conformation. As the super¯uidity and superconductivity, but neither seems to proteins relax, they emit vibrational energy in the form of have an obvious equivalent in the brain. Certainly there is phonons 'the sound equivalent of photons) with their nothing structurally comparable to the delocalization of wavelength in phase synchrony. A coherent, non-local electrons in a piece of copper wire, or to suggest that the order emerges. brain can sustain a state of zero resistance to the movement The idea is a pleasing one: consciousness is the melody of electrons across space.