I thank professors Spier and Thomas for their interest and forthright criticism. At first glance a link between consciousness and a basic level of the universe is indeed a strange departure and their skepticism understandable. However the "hard problem" of conscious experience demands new ideas. The Penrose-Hameroff Orch OR model encompasses not only physics, but also philosophy, neuroscience, cognitive psychology, computer science, molecular biology and evolution [1-3]. Such an integrated, multi-level assault is required for any serious attempt. Rather than dualist, our view is monist in that both mind and body ensue from particular processes and configurations in fundamental spacetime geometry. Oxford philosopher Galen Strawson [4] describes such a view as "realistic monism".

How did we arrive at this conclusion? Roger Penrose*s non-computability was the clue, a thread with which to unravel larger mysteries such as the nature of experience and free will. Roger followed this thread, seeking a non-computable physical process which could occur in the brain. As a candidate he nominated a particular type of self-organizing collapse of the quantum wave function (objective reduction - OR) [5-8].

In the Penrose view quantum superpositions (e.g. two alternate states or locations of an object existing simultaneously) are actually slight separations ("bubbles") in the underlying makeup of reality (spacetime geometry). If isolated and thus able to persist, the separations become unstable and eventually reach a threshold for collapse (this instability in spacetime separation is the link to quantum gravity). At the instant of collapse each spacetime bubble reduces to a definite, unseparated state as an OR event occurs. In each event the choice of state is selected non-computably to reflect some influence which is neither random nor completely deterministic, but due to hidden propensities embedded in fundamental spacetime. A series of such events may be seen as a pattern of bubbles and ripples at the smallest scale in the makeup of reality.

How does this relate to the problem of experience? Panpsychist and pan-experiential philosophers have been claiming for thousands of years that varieties of proto-conscious experience (*qualia*) are intrinsic properties of reality. Qualia may be particular patterns in fundamental spacetime geometry, for example encoded in Planck scale spin networks. OR events may occur in and of an experiential medium.

Regarding free will, the problem is that our actions seem neither totally deterministic nor random (probabilistic). The only other apparent choice is Penrose*s non-computability. In the Orch OR model microtubule quantum superpositions compute and evolve linearly (analogous to a quantum computer) during pre-conscious processing, but are influenced at the instant of OR collapse by hidden (Platonic) non-computable logic inherent in spacetime geometry. The precise outcome¿our free will actions¿result from effects of the hidden logic on the quantum system poised at the edge of objective reduction.

As illustration consider a sailboard in which a sailor sets the sail in a certain way; the direction the board sails is determined by the action of the wind on the sail (Figure 1). Pretend the sailor is a non-conscious robot zombie run by a quantum computer which is trained and programmed to sail. Setting and adjusting of the sail, sensing the wind and so forth are algorithmic and deterministic, and analogous to the pre-conscious, quantum computing phase of Orch OR. Direction and intensity of the wind (seemingly capricious, or unpredictable) are analogous to hidden non-local variables (e.g. "Platonic" quantum-mathematical logic inherent in space-time geometry). The choice, or outcome (the direction the board sails, the point on shore it lands) depends on deterministic sail settings acted on repeatedly by the apparently unpredictable wind. Our "free will" actions could be the net result of deterministic processes acted on by hidden quantum logic at each Orch OR event.

To this point Spier and Thomas raise an appropriate objection: "since there must be only one Platonic logic, all agents performing under it must hold the same opinions". There are several reasons for this not to be the case. First, Planck scale geometry may be evolving and thus variable over time [9]. Secondly, its influence would still be subject to the vagaries of individual personalities and potentially over-riding deterministic processes. Consequently reactions may vary due to genetic influences, learned behavior and intensity of deterministic drives. Thirdly, effects of the proposed hidden propensities (on protein conformation) are subtle, requiring a properly susceptible "frame of mind".

I completely agree with Spier and Thomas that protein molecules "act as the basic computational elements in living cells", but simply add that proteins may act as quantum computational elements. Proteins are dynamical¿their state a delicate balance among various countervailing forces. However strong forces cancel out so that dynamical protein conformation and function are determined by weak quantum-level dipole interactions called London (van der Waals) forces [10]. These forces largely occur in intra-protein hydrophobic pockets, water-excluding regions at which anesthetic molecules act [11]. If proteins are quantum switches, then an interactive protein lattice (e.g. microtubules) could constitute a quantum computer.

Spier and Thomas also argue that "microtubules are too unstable to account for consciousness". While this is true of non-neuronal dividing cells whose microtubules radiate from centrioles and are (as Spier and Thomas describe) dynamically unstable, neurons in the brain don*t divide, their microtubules do not radiate from centrioles, and they do not manifest dynamic instability [12]. Brain microtubules are quite stable and interlinked in complex cytoskeletal networks.

Is the single cell animal paramecium conscious? Spier and Thomas assume that the Orch OR position is yes because we describe intelligent paramecium behavior mediated by microtubules. In fact we do not claim a paramecium is conscious. Based on an upper limit of hundreds of milliseconds of sustained quantum coherence, the Orch OR model predicts a lower limit for consciousness at the level of about 300 neurons (e.g. small worms and urchins). A single cell paramecium, while clever, seems unlikely to sustain sufficient quantum coherence to reach threshold for OR reduction (e.g. up to one minute would be required), and is thus unlikely to attain conscious experience [13]. One may question even rudimentary consciousness in small worms ("what is it like to be a worm?") but unlike any other theory Orch OR is at least able to make such a prediction.

What about even more primitive cells? Spier and Thomas observe that bacteria which also seem computationally driven lack microtubules, questioning their necessity for intracellular information processing. However such bacteria do have "protein-based circuits", and recent evidence show the structure of such proteins to be strikingly similar to the microtubule protein tubulin [14]. Bacteria have primitive forms of microtubules. Although Orch OR predicts emergence of consciousness at roughly 300 neurons, pre-conscious protein-based quantum computation may be an essential feature of all living protoplasm.

Finally, Spier and Thomas ask what it is in Orch OR which "does the work of the mind"? Like other theories the answer is mainly glucose and oxygen. We discard nothing from conventional theories except the assumption that consciousness emerges completely from membrane-level computational complexity. If one views a particular conscious experience or volitional choice as correlating with a particular neural network settling into specific attractor dynamics, one may continue to do so and simply add underlying regulation by quantum computation in microtubules. Orch OR is a funda-mental extension of neural-level theories of consciousness.

References

1. Hameroff, S. (1998) Funda-mental geometry: The Penrose-Hameroff Orch OR model of consciousness. In: Geometry and the Foundations of Science. Contributions from an Oxford conference honoring Roger Penrose. Oxford Press (in press)
2. Hameroff, S (1998) "More neural than thou": Reply to Churchland's "Brainshy" in: Toward a Science of Consciousness II - The Second Tucson Discussions and Debates. Eds S Hameroff, A Kaszniak, A Scott. MIT Press, in press
3. Hameroff, S (1998) Did consciousness cause the Cambrian evolutionary explosion? in: Toward a Science of Consciousness II - The Second Tucson Discussions and Debates. Eds S Hameroff, A Kaszniak, A Scott. MIT Press, in press
4. Strawson G (1998) Realistic monism. Abstracts of "Toward a Science of Consciousness 1998 (Tucson III)" April 27-May 2, Tucson, Arizona, Imprint Academic in press
5. Penrose, R. (1989) The Emperor's New Mind, Oxford Press, Oxford, U.K.
6. Penrose, R. (1994) Shadows of the Mind, Oxford Press, Oxford, U.K.
7. Penrose, R. (1996) On gravity's role in quantum state reduction. General relativity and gravitation. 28(5): 581-600
8. Penrose, R. (1997) On understanding understanding. International Studies in the Philosophy of Science 11(1):7-20.
9. Smolin, L. (1997) Life of the Cosmos, Oxford Press, N.Y.
10. Voet, D., Voet, J.G. (1995) Biochemistry, 2nd edition. Wiley, New York.
11. Franks, N.P., and Lieb, W.R. (1982) Molecular mechanisms of general anesthesia. Nature 316:349-351
12. Penrose, R., Hameroff, S.R. (1995) What gaps? Reply to Grush and Churchland. Journal of Consciousness Studies 2(2):99-112.
13. Hameroff, S.R., and Penrose, R. (1996b) Conscious events as orchestrated spacetime selections. Journal of Consciousness Studies 3(1):36-53
14. L"we J, Amos LA (1998) Crystal structure of the bacterial cell-division protein FtsZ. Nature 391: 203-206

Figure 1. An analogy for free will. In Orch OR our actions are the result of non-computable influences acting on deterministic processes poised at the brink of objective reduction. To illustrate, a deterministic robot zombie is programmed to algorithmically sail to ports A,B or C. The direction the board sails (and the port at which it lands) is the result of seemingly capricious (non-computable) wind acting on the sailor*s deterministic actions.