A place for consciousness in nature
Perspective on ‘Conscious events as orchestrated space-time selections’
by Hameroff and Penrose
in
The Nature of Nature:
Examining the Role of Naturalism in Science
Bruce L. Gordon and William A. Dembski, eds., (Wilmington, Del.: ISI Books, 2009).
Stuart Hameroff
Professor, Departments of Anesthesiology and Psychology
Director, Center for Consciousness Studies
The University of Arizona, Tucson, Arizona
The article ‘Conscious events as orchestrated space-time selections’ was written by Sir Roger Penrose and me for a special issue of the Journal of Consciousness Studies devoted to the ‘hard problem’ [1]. Coined by philosopher David Chalmers [2], the term ‘hard problem’ refers to the enigmatic question of how the brain produces conscious awareness, subjective feelings and phenomenal experience – composed of what philosophers call ‘qualia’.
On the other hand, non-conscious cognitive brain functions including sensory processing and control of habitual behaviors can be explained by computation among brain neurons in which axonal firings and synaptic transmissions play the roles of ‘bit’ states and switches. Though complex, these non-conscious brain functions are referred to as ‘easy problems’ [2], ‘zombie modes’ [3], or ‘auto-pilot’ [4]. Many neuroscientists and philosophers dispute or disregard the hard problem and assume and assert that consciousness emerges as an epiphenomenon of neuron-based complex computation. Indeed, the idea that consciousness involves something in addition to neuronal computing has been derided as dualism, as expecting a ‘ghost in the machine’ [5]. Accordingly, proponents of ‘strong’ artificial intelligence (AI) argue that silicon computers will inevitably attain brain equivalence including conscious awareness [6].
In his 1989 book The Emperor’s New Mind, Roger Penrose [7] laid out an argument against strong AI through Gödel’s theorem, contending that consciousness required something beyond classical computation, some ‘non-computable’ element which influenced or augmented the computation. The missing ingredient in consciousness, Penrose suggested, was a specific form of quantum computing in the brain.
Quantum computing utilizes strange properties of the quantum world, differing markedly from those of our everyday classical world. Quantum properties include quantum superposition in which particles exist in multiple states or locations simultaneously, e.g. as quantum bits, or ‘qubits’ which interact/compute with other qubits by entanglement. In a quantum computer, superpositioned, entangled qubits eventually reduce (‘collapse’) to classical bits as the solution. Mechanisms underlying quantum state reduction - ‘collapse of the wave function’ – in quantum computing (and nature in general) are not understood, although numerous theories exist. One view stemming from Niels Bohr is that quantum systems persist until consciously observed – that conscious observation causes collapse of the wave function. This pragmatic view puts consciousness outside science.
Penrose turned this view around. He introduced a new theory of self-collapse - quantum state reduction due to a specific objective threshold (‘objective reduction’, ‘OR’). Rather than being caused by conscious observation, each OR event entails a conscious perception or choice. To identify the threshold for such conscious OR events, Penrose first characterized superpositions as separations in fundamental space-time geometry, the level of quantum gravity at the Planck scale [8]. He further proposed that such objective reduction/conscious events could be influenced by Platonic information, e.g. mathematical truth, but also perhaps ethical and aesthetic values embedded in Planck scale geometry. These Platonic values could influence (‘non-computably’) the output of a quantum computation mediated by this type of OR. Penrose thus placed consciousness in nature, precisely on the edge between quantum and classical worlds.
Penrose was calling for a particular form of quantum computation in the brain to explain consciousness. As qubits, he suggested that neurons could exist in superposition of both firing and not firing, but worried that neurons were too large for quantum effects and left the door open for a biomolecular qubit. When I read The Emperor’s New Mind in the early 1990s, I was struck and somewhat bewildered by the breadth and depth of Penrose’s arguments leading to this seemingly strange conclusion. He was obviously brilliant, and he had a theory which portrayed consciousness as actual physical events, if as yet theoretical physical events.
I readily agreed that consciousness involved something other than computation among neurons, having worked for twenty years on the premise that consciousness extended inside neurons. In medical school I had become obsessed with the notion of molecular-scale computing in cytoskeletal structures called microtubules which regulate synapses and axonal firings from within neurons [9-11]. I believed that viewing neurons as simple input-output devices was an insult to neurons, but also realized that extending computation inside neurons (and increasing brain computational capacity enormously) didn’t solve the hard problem. As an anesthesiologist, I had also studied how anesthetic gases selectively erase consciousness through quantum London forces [12,13], and knew the work of Herbert Fröhlich [14,15] who had proposed biochemically-driven quantum coherence in biomolecular lattices such as microtubules. I was open to new ideas, including quantum computing in the brain. Maybe tubulins were qubits, and microtubules were the quantum computers Penrose sought?
I contacted Penrose, and we soon met in his cluttered Oxford office. He was, and is, a remarkable man, both gentle and strong with an open but critical mind. As I described microtubules he was most impressed by their symmetry and geometry. We began collaborating toward a theoretical model [1, 16-19].
We faced difficult issues. Technological quantum computers required isolation and extreme cold to avoid environmental decoherence, so quantum computing in the warm brain seemed extremely unlikely [20,21]. And even if quantum computing could occur in one neuron, how could it extend globally across cell boundaries throughout the brain? And if quantum systems were isolated within the brain, how could they interact with the external world for input and output? Regarding the latter, Penrose and I described consciousness as a sequence of discrete OR-mediated quantum computations occurring at frequencies compatible with brain electrophysiology, such as EEG rhythms ranging from 2 Hz to 40 Hz or higher. In the classical intervals between such isolated quantum events, neurons could express outputs to the external world, and synaptic inputs could ‘orchestrate’ OR-mediated quantum computing via microtubule-associated proteins (‘Orch OR’).
Casting consciousness as sequences of discrete events made Orch OR compatible not only with brain electrophysiology and OR quantum physics, but also with the work of process philosopher Alfred North Whitehead [22]. Consciousness, according to Whitehead, was a series of ‘occasions of experience’ occurring in a ‘wider, basic field of proto-consciousness’. As quantum state reductions, Orch OR events qualified as Whitehead ‘occasions’. Regarding the ‘wider, basic field’, Penrose and I pointed to fundamental spacetime geometry at the Planck scale in which Orch OR was suggested to occur. Penrose had placed Platonic values there, and for our ‘hard problem’ paper reproduced here, we added proto-conscious qualia, or experience as an irreducible component of fundamental spacetime geometry, akin to other irreducible components like mass, spin or charge. Orch OR became consistent with Whitehead’s philosophical construct containing consciousness.
Orch OR came under heavy attack, primarily on the issue of decoherence in the warm brain [20,21]. But evidence in recent years has revealed quantum coherent superposition in warm biomolecules and proteins, specifically in the type of non-polar hydrophobic pockets which mediate anesthetic effects and are foci of tubulin quantum states in Orch OR [23,24]. Fröhlich coherence has been demonstrated in microtubules at 8 MHz [25]. Penrose OR is being tested as an explanation for quantum state reduction [26].
In 1998 I published a list of 20 testable predictions of Orch OR [18], some of which have been corroborated [27]. For example, to account for extension of isolated quantum states in one neuron to global neuronal assemblies spanning the brain, neurons involved in conscious processes were proposed to require linkage by gap junctions, window-like connections which fuse and synchronize neighboring neurons and glia, and through which quantum states could extend by quantum tunneling. In recent years, gap junctions between brain neuronal dendrites have been shown to be essential for gamma synchrony EEG (~40 Hz), the best measurable correlate of consciousness [28,29]. Considering that habitual cognitive brain functions like driving or walking could at times be non-conscious easy problems (zombie modes, auto-pilot), and at other times be accompanied by conscious perception and control, I proposed a ‘conscious pilot’ model in which gap junction-defined spatiotemporal envelopes of gamma synchrony (within which Orch OR can occur) move through the brain as a mobile agent (the ‘conscious pilot’) to consciously perceive and control otherwise non-conscious auto-pilot modes [30]. The Orch OR conscious pilot may be seen as an actual quantum ‘ghost in the machine’.
Orch OR encompasses aspects of philosophy, neuroscience and physics, goes out on several limbs simultaneously, and contains much to criticize. But as yet, Orch OR has weathered every objection [31,32] and remains the most ambitious and complete theory of consciousness yet put forward. Most importantly, it characterizes consciousness not as epiphenomenon, but as intrinsic component of the universe, a process of actual events, of Whitehead ‘occasions of experience’ occurring on the edge between quantum and classical worlds. Moreover non-computable Platonic information in spacetime geometry can influence not only conscious thoughts and behaviors, but also life and evolution through quantum-level mutations in DNA [33].
References
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