SUMMARY: ORCHESTRATED OBJECTIVE REDUCTION (Orch OR) OF QUANTUM COHERENCE IN BRAIN MICROTUBULES
The picture we are putting forth involves the following ingredients:
A) A macroscopic state of quantum coherent superposition can exist among tubulin subunits in microtubules across a large proportion of the brain. Plausible candidates for such states include models proposed by:
1) Marshall (1989) in which Frû…lich pumped phonons induce a Bose-Einstein condensate among proteins distributed throughout the brain
2) Jibu et al (1994) in which ordered water within microtubule hollow cores is coupled to Fröhlich excitations of tubulins in microtubule walls
resulting in coherent photons ("super-radiance" 3) Kaivarainen (1995) in which quantum coherent "flickering"clusters of ordered water within hollow microtubule cores are coupled to (non-Fröhlich) tubulin conformational dynamics and generate coherent photons
4) Conrad (e.g. this Volume) in which conformational states and functional capabilities of proteins are controlled by quantum superposition dynamics of electrons and hydrogen bonds within them.
B) The quantum coherent state is weakly coupled to conformational activity taking place in tubulins within microtubules. The link occurs by changes in individual electric dipole moments within tubulins. For example movements of a single electron within a hydrophobic pocket centrally placed within each tubulin dimer may couple to the conformational state of the tubulin (Figure 4).
C) This combined quantum state among many tubulins is able to maintain itself without significant entanglement with its environment for a relevant period of time (up to 500 msec). We envisage several possible mechanisms which could serve to isolate the MT quantum state from its environment within the neuron. These include (see Section 5.2):
Shielding by ordered water on tubulin surfaces
Isolation within hollow MT inner cores
Shielding by gelatinous cytoplasmic layer
D) Cooperative interactions among neighboring tubulins in microtubules can signal and process information by computational mechanisms such as cellular automata behavior. We propose two types of microtubule computation:
Classical computing: conformational patterns propagate through the cytoskeleton to regulate synapses and perform other neural functions (Figure 5). This mode correlates with non-conscious and autonomic activities.
Quantum computing: large scale quantum coherence occurs among tubulins (e.g. via electrons in hydrophobic pockets arrayed in the microtubule lattice) and takes on aspects of a quantum computer (e.g. Deutsch, 1985; Deutsch and Josza 1992; Feynman 1986; Benioff; 1982) where multiple "computations"are performed simultaneously, in parallel, according to quantum linear superposition. We equate quantum computing with pre-and sub-conscious processing.
E) In the quantum computing mode, changes in dimer conformations involve the movement of mass. According to the arguments and criterion described in Section 5.1), we estimate the time scale T , and calculate the number n(sub)t (of coherent superpositioned tubulins) required for self collapse (objective orchestrated reduction: Orch OR) to occur. As we equate quantum computing with pre-conscious processing, we approximate the time scale to be equivalent in some cases to that found by Libet et al (1979) and others (e.g. Deeke et al, 1976; Grey-Walter, 1953) to be characteristic of the transition from pre-conscious to conscious processing (up to 500 msec). For T =500 msec, we get a rough estimate of 109 tubulins required for Orch OR.
F) Microtubule associated proteins (MAPs) attached to certain microtubule tubulin subunits would seem likely to communicate the quantum state to the outside "noisy"random environment, and thereby entangle andcollapse it (SR, or R). We therefore presume that these MAP connections are placed along each MT at sites which are (temporarily at least) inactive with regard to quantum-coupled conformational changes. We envisage that these connection points are, in effect, "nodes"for MT quantum oscillations, and (along with genetic and other tubulin modifications) thus "orchestrate"MT quantum coherence and subsequent OR (Figure 8). Accordingly, we term the particular objective reduction (OR) occurring in MTs and relevant to consciousness as "orchestrated objective reduction"(Orch OR).
G) The Orch OR process selects a new set of tubulin conformational states ("eigenstates of mass distribution" within MTs which can implement and regulate neural function by determining MAP attachment sites and setting initial conditions for "cellular automata"information processing by "classical"conformational transitions. These MT activities can then govern intra-neuronal architecture and synaptic function through modulating sensitivity of membrane receptors, ion channels and synaptic vesicle release mechanisms, communication with genetic material, andregulating axoplasmic transport which accounts for delivery of synaptic material components.
H) How is a particular conformational pattern within each microtubule chosen in the Orch OR process? The Copenhagen quantum interpretation would suggest the selection of states upon (SR, or R) collapse is purely random. Effects of MAPs, genetic and other tubulin modifications can set the possibilities and probabilities ("orchestrate", but reduction within that context is non-computable. As described in Shadows of the Mind (Penrose, 1994), it remains possible that presently unrecognized OR (or Orch OR) quantum-mathematical logic acting on these programming influencesprovides a hidden order.
I) Because OR (and Orch OR) phenomena are fundamentally non-local, the coherent superposition phase may exhibit puzzling bidirectional time flow prior to self-collapse (e.g. Aharonov and Vaidman, 1990; Penrose 1989; 1994). We equate the pre-collapse quantum computing superposition phase to pre-conscious processing. This could explain the puzzling "backwards time referral"aspects of pre-conscious processing observed by Libet et al (1979). (Also see Tollaksen, this Volume.)
J) The persistence and global nature of consciousness is seen as a feature of large scale quantum coherent activity taking place across much of the brain. Varieties of Orch OR with differing coherence times and amounts of coherent tubulin may blend into conscious thought. Very intense, sudden inputs may recruit emergence of quantum coherent tubulins faster than 500 msec so that Orch OR occurs sooner ("heightened"experience, Figure 11c). Lower intensity, unexciting input patterns develop coherence more slowly and Orch OR occurs later. An instantaneous Orch OR may then "bind" disparate tubulin superpositions which may have evolved in separate spatial distributions and over different time scales into an instantaneous conscious "now" Cascades of Orch ORs can then represent our familiar "stream of consciousness."
7 CONCLUSION
Approaches to understanding consciousness which are based on known and experimentally observed neuroscience fail to explain certain critical aspects. These include a unitary sense of binding, non-computational aspects of conscious thinking, difference and transition between pre-conscious and conscious processing, (apparent) non-deterministic free will and the essential nature of our experience. We conclude that aspects of quantum theory (e.g. quantum coherence) and of a newly proposed physical phenomenon of wave function self-collapse (objective reduction, OR, Penrose, 1994) offer possible solutions to each of these problematic features. We further conclude that cytoskeletal microtubules, which regulate intra-neuronal activities and have cylindrical paracrystalline structure, are the best candidates for sites of quantum action and OR, and of "orchestrated OR"(Orch OR). Accordingly, we present a model of consciousness based on the following assumptions:
Coherent excitations (Fr&ounl;hlich pumped phonons) among microtubule subunits (tubulins) support "cellular automaton"information processing in both classical (conformational) and quantum coherent superposition modes. Classical processing correlates with non-conscious, autonomic activity; quantum processing correlates with pre-and sub-conscious activity.
The microtubule quantum coherent computing phase is able to be isolated from environmental interaction and maintain coherence for up to 500 msec (pre-conscious processing).
A critical number of tubulins maintaining coherence within MTs for 500 msec collapses its own wave function (objective reduction: OR). This occurs because the mass-energy difference among the superpositioned states of coherent tubulins critically perturbs space-time geometry. To prevent multiple universes, the system must reduce to a single space-time by choosing eigenstates. The threshold for OR is related to quantum gravity; we calculate it in terms of the number of tubulins coherent for 500 msec to be very roughly 109 tubulins. Larger coherent sets will self-collapse faster, and smaller sets more slowly. Coherent sets which evolve over different time scales and in different brain distributions may be bound in an effectively simultaneous collapse which creates instantaneous "now" Cascades of these events constitute the familiar "stream of consciousness"
.Microtubule associated proteins (MAPs) and other tubulin modifications act as "nodes"to tune microtubule coherence and help to orchestrate collapse. We thus term the specific OR proposed to occur in microtubules and intrinsic to consciousness as "orchestrated objective reduction"(Orch OR).
.The Orch OR process, which introduces non-computability (Penrose, 1989; 1994), results in eigenstate patterns of tubulin conformational states which help direct neural function through the actions of microtubules.
In providing a connection among 1) pre-conscious to conscious transition, 2) fundamental space-time notions, 3) non-computability, and 4) binding of various (time scale and spatial) superpositions into instantaneous "now" we believe Orch OR in MTs is the most specific and plausible model for consciousness yet proposed.
http://www.quantumconsciousness.org/pen ... rchOR.html