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Schrödinger’s Neurons
by David Pearce
An experimentally testable explanation of conscious mind



Any scientific theory of conscious mind should explain (1) why consciousness exists at all (the “Hard Problem”) (2) how consciousness could be locally or globally bound by a pack of membrane-bound, supposedly classical neurons (the phenomenal binding / combination problem) (3) how consciousness exerts the causal power to allow us to discuss its existence (the problem of causal impotence versus causal over-determination) (4) how and why consciousness has its countless textures and the interdependencies of their different values (the "palette problem"). Yet above all, any adequate scientific theory of consciousness should offer novel, precise and empirically falsifiable predictions, not mere retrodictions. A good scientific conjecture should be in Popper’s sense “risky”. The predictions should be robust and replicable. Further, the outcome of a well-designed experimental test should - by antecedent agreement - satisfy both proponents and critics.

The protocol is outlined of a molecular matter-wave interferometry experiment designed to test what is naively the reductio ad absurdum of quantum mind. The conjecture is as follows. Phenomenal binding of distributed neuronal feature-processors in the CNS is classically impossible. Instead, phenomenal binding consists of quantum-coherent superpositions of neurons at sub-femtosecond timescales. The phenomenally-bound classical world-simulation of one’s everyday experience consists in sequences of neuronal “Schrödinger’s cat states” harnessed via selection pressure to track fitness-relevant patterns in the local environment. More poetically, our phenomenally bound minds are akin to a movie or virtual reality world-simulation running at around 1015 quantum-coherent frames per second.


If monistic physicalism is true, no "element of reality" can be missing from the formalism of our best theory of the world. Hence the mystery of consciousness in the physical universe. Faced with the Hard Problem, a minority of researchers have proposed that experience discloses the intrinsic nature of the physical - the mysterious "fire" in the equations on which physics is silent. No “strong” emergence exists in Nature; and nor is there a problem of causal efficacy or over-determination because consciousness is the “fire” itself: Kant’s noumenal essence of the world. Such a conjecture – variously called constitutive panpsychism, Strawsonian physicalism, physicalistic idealism or non-materialist physicalism - about the intrinsic nature of the physical is exceedingly far-fetched because the hypothetical fundamental "psychon" of conscious experience is both implausibly small and implausibly short-lived. Implausibility aside, however, constitutive panpsychism faces two substantive challenges: the palette problem or the argument from microphysical simplicity; and the phenomenal binding problem, aka the argument from structural mismatch. The palette problem is soluble, in principle, if we shed the particle-based ontology of introductory quantum mechanics and adopt a field-based ontology: the diverse solutions to the equations of relativistic quantum field theory yield the diverse micro-values of experience. Unfortunately, such a conjecture doesn’t seem experimentally testable. So what about the combination/binding problem? Why aren't we just micro-experiential zombies, mere patterns of Jamesian “mind-dust”? Phenomenal binding of discrete and decohered membrane-bound neurons is classically impossible. Hence the spectre of Chalmersian dualism.

Yet monistic physicalism can still potentially be saved – and testably so. If (1) physicalism is true (2) consciousness discloses the intrinsic nature of the physical (3) and the unitary Schrödinger dynamics doesn’t break down in the CNS, then the existence of phenomenal binding in the guise of individual neuronal superpositions isn’t optional: it's inescapable. Intuitively, for sure, the notional mental superglue of individual sub-femtosecond neuronal superpositions of distributed feature-processors is computationally useless - of no more phenomenal significance than, say, undetectable sub-zeptosecond superpositions of pawns in a game of chess. For if such coherent superpositions fleetingly exist at all, neuronal superpositions are just random psychotic noise, impotent to "save the phenomena". Intuitively, thermally-induced decoherence - the scrambling of phase angles between components of an individual neuronal superposition - is much too rapid in the warm, wet CNS for selection pressure to harness such superpositions - in humans if not navigating robins. The dynamical timescale for a "Schrödinger’s neurons" conjecture would seem wrong by many orders of magnitude. For (we normally assume that) phenomenally-bound conscious states of mind must “emerge” on a time-scale of milliseconds via (somehow) patterns of classical neuronal firings. By contrast, even the most robust neuronal superpositions will be “destroyed” (i.e. their quantum coherence is irreversibly delocalised into the larger CNS-environment combination though uncontrolled environmental entanglement) over naively ludicrously short time-scales.


Maybe so. The interferometry experiment outlined puts our commonsense intuitions to the test. Barring some revolutionary breakthrough, in vivo interferometry to probe neuronal superpositions in the CNS is beyond the reach of twenty-first century technology. However, live subjects aren't needed to test the non-classical basis of phenomenal binding. Cultured in vitro neuronal networks should suffice. First, "train up" a multi-layer neuronal network with a suitable input-output device to recognise a variety of externally presented inputs. Then, identify the distributed neuronal feature-processors implicated in diverse object recognition on a standard, classically parallel connectionist account, i.e. the "local" phenomenal binding of perceptual objects. Routine neuroscanning can pick out what we would naively describe as the synchronously activated distributed neuronal feature-processors elicited by any given stimulus, i.e. textbook connectionist neuroscience but using real neurons rather than tendentiously named "artificial neural networks" and their statistical learning algorithms.

Three experimental outcomes are possible:

  1. no telltale non-classical interference pattern. (Copenhagen, “dynamical collapse” interpretations, GRW, etc)
  2. a non-classical interference pattern that’s just random neural noise. (e.g. Tegmark, Schlosshauer)
  3. A perfect structural match.
Our conjecture predicts (3). Instead of no interference signature (1), or the interference patterns of "nonsense" neuronal superpositions (2), we'll discover the non-classical interference signature of sub-femtosecond macro-superpositions that robustly implicate exactly the same neuronal feature-processors of the synchronously activated neurons that the standard neuroscience story reports are activated in the trained-up neuronal network when perceptual object-recognition occurs (3). Binding-by-synchrony is really binding-by-superposition. On any classical account of mind, such an experimental outcome is physically impossible.