Is Tryptophan the gate to consciousness?
& should the Penrose/Hameroff theory be inverted/simplified
Refers to talks by Travis Craddock (University of Alberta) and Rafael Malach (Weizmann Institute)
The argument as to whether quantum coherence could be related to consciousness underwent a fundamental shift in 2007. Up to that time the sceptics had a prima facie case against coherence being able to survive for sufficiently long to be relevant to brain functions. Proponents of coherence could suggest forms of shielding within neurons, but there was no very specific evidence for this.
However, in 2007 a study by Greg Engel, published in Nature, revealed the existence of quantum coherence in biological tissues. This initial study referred to green sulphur bacteria, which are photosynthetic organisms living at the very low temperature of 77K. However, subsequent research has greatly widened the scope of photosynthetic coherence. A 2010 paper by Elisabetta Collini et al, also published in Nature, showed similar coherence in marine algae at room temperature, and another paper has indicated quantum coherence in higher plants. These latter papers carry with them the suggestion that quantum coherence may be general in photosynthetic organisms rather than a peculiarity of extreme conditions.
It is thought very likely that the quantum coherence detected does play a functional role in photosynthetic organisms because it resolves the puzzle of the very high level of efficiency (97-99%) in energy transfer between the light harvesting antennae of these organisms and the reaction centres where the process of utilising the energy gathered begins. Most researchers in this area think that quantum entanglement is also present in these photosynthetic organisms, although they are much less certain as to whether this has any role in the functioning of the organisms.
The Engel (2007) paper removed the main plank of the arguments against quantum coherence in the brain. Much of the criticism directed at quantum consciousness amounts to no more than a bluster of aggression, ridicule and ignorance, but the argument that quantum states would decohere too quickly to be relevant to brain functions is based on sound physics. However, the Engel paper showed that contrary to the common sense if rather simplistic approach of this argument, quantum features could in fact be functional in biological tissue.
The surprising thing is the near silence that greeted this discovery not only in biology and mainstream consciousness studies, but even in the area of quantum consciousness studies. Research into photosynthetic quantum coherence is orientated towards its relevance for quantum computing and/or energy extraction from some form of artificial photosynthesis. The relevance to quantum consciousness, which would not be helpful for funding or peer review, has been ignored except for the occasional dismissive comment. The most detailed attempt at this, by Greg Scholes, fell into the common error of thinking that quantum consciousness was supposed to happen at the level of whole neurons, rather than at the same electron level that is involved in photosynthetic coherence. I have yet to see a single comment on photosynthetic coherence within mainstream consciousness material, but this is not surprising given that this area seems to become ever more abstracted from current scientific research, even that of conventional neuroscience.What is more surprising, however, is the lack of response from the small corp of quantum consciousness researchers who so badly need support for their much ridiculed cause. Although Hameroff sometimes refers to the photosynthetic studies as general support for quantum coherence in the brain, he has not attempted to integrate his hypothesis with the evidence-based coherence of photosynthetic organisms. The same applies to Gustav Bernroider‘s interesting theory of quantum coherence and consciousness arising in the ion channels. One problem that looms large, and has been given insufficient attention, is the gulf between photosynthetic coherence and the Hameroff model, in terms of how long coherence survives. Photosynthetic coherence is measured in femto or at best pico seconds, while the Hameroff model demands a more ambitious 25 ms.
The recent Stockholm consciousness conference was frustrating in respect of this lack of engagement with the questions and possibilities raised by photosynthetic coherence, and only in the last afternoon did something interesting in this respect emerge. Could what was known to be going on in photosynthetic organisms have anything to do with mechanisms in the brain? A brief talk by Travis Craddock of the University of Alberta in the last workshop of the conference suggested that it could.
Craddock stresses that light absorbing chromophore molecules involved in light harvesting use dipoles to provide 99% efficiency in energy transfer from the light harvesting antennae to the reaction centre. The studies show that instead of quantum coherence being destroyed by the environment within the organism, a limited amount of noise in the environment acts to drive the system. Craddock indicates that any system of dipoles could work like this. He is particularly interested in the role of the amino acid, tryptophan. Similar models can be used for chromophores in photosynthetic systems and for tryptophan, an aromatic amino acid that is one of the 20 standard amino acids making up protein. Tryptophan has eight molecules extending over the length of the tubulin protein dimer, and it possesses strong transition dipoles. Excitons over this network are not localised, but are shared between all the tryptophan molecules, in the same way that excitons are delocalised in the photosynthetic light-harvesting structures. Photosynthesis absorbs light in the red and infra red. These forms of light are not available to tryptophan in proteins, but tryptophan is able to use ultra violet light emitted by the mitochondria. In fact Tryptophan is sometimes referred to as chromophoric because of its ability to absorb UV light. Craddock implies that the same system that gives rise to quantum coherence in light-harvesting complexes could also give rise to it within the protein of neurons.
Should the Hameroff model be inverted? – I think that the relative simplicity of the light harvesting concept in photosynthetic systems and of tryptophan in microtubules may hint at a simpler model for quantum consciousness. The Hameroff model envisages coherence arising in the microtubules, but then spreading to other neurons via dendritic gap junctions, until coherence and probably entanglement embraces all the regions of the brain involved in a particular instance of global gamma synchrony, with wave function collapse every 25 ms, to tie in with the 40 Hz gamma synchrony. This is the most specific and elaborate quantum consciousness model, and as such it has laid itself open to numerous if often simplistic attempts at refutation at many points along its extended structure. In particular the requirement to maintain coherence over an extended system for 25 ms is very demanding, even accepting that the arguments about rapid decoherence in the brain have not proved as watertight as some expected.
Convergence on specialised neurons: – A recent study by Rafael Malach of the Weizmann Institute indicates that while perception involves widespread cortical processing, the emergence of an actual perception involves only a small number of localised hot spots, in which there is intense and persistent gamma activity. Malach used the well-researched area of face recognition to clarify this concept. Studies indicate the existence of so-called totem cells (a reference to totem poles with carved faces) that are able to recognise a number of faces. The hot spots are suggested to involve intense activity between several of these totem neurons resulting in a sort of vote. If the same face is recognised by a majority or most of the neurons, the face is consciously recognised. The presumption seems to be that this would apply for most forms of perception and not just face recognition.
Malach’s studies hints at important possibilities. Firstly it raises the game for the individual neuron, from a simple switch to a computer and possibly a super computer. If we accept a conscious processing role for the individual neuron, it puts a different light on the global gamma synchrony, as a probably classical structure that simply coordinates the activity of a number of hot-spot neurons, in order to produce the unity of consciousness. In Malach’s example, face-recognition is not the end of the problem, because we do not usually perceive faces in isolation but as part of an environment. This suggests that the gamma synchrony could ensure that face recognition was coordinated with other hot-spot neurons that recognise clothing, furniture, a room or a surrounding landscape. This could imply that the type of quantum coherence and probably entanglement seen in photosynthetic organisms, and suggested to exist in tryptophan, could operate to produce consciousness in individual neurons, which is then unified by the gamma synchrony.
Penrose simplified? – Even Penrose’s proposition that there is a requirement for a special type of wave function collapse (objective reduction), distinct from the normal randomness of wave function collapse, in order to access the fundamental spacetime level might be over complex. Penrose, in common with some of the critics of quantum consciousness, took it that the randomness of collapse was a not a useful basis for conscious understanding, and he proposed that non-computable processing arose when quanta were separated from the environment for long enough to undergo a form of self-collapse.
But is the normal wave function collapse so useless? Because randomness is used so much in everyday speech, we have to be careful about what we mean by randomness. We can say that the buses arrive at random intervals, but we know that the actual process could be expressed in terms of an algorithm, and lotteries are pseudo-random, with the winning numbers generated by an algorithm.
However, this is not true of the wave function collapse, where the choice of position of an individual quanta just happens, and represents an effect without a cause, outside of the normal process and mathematics of both classical and quantum physics. And yet with any large number of quanta a pattern will emerge. In a version of the two-slit experiment, photon’s are passed through the apparatus individually at separate times, and fall randomly on the final screen, and yet over time these separated photons form the well-known interference pattern of dark and light bands. Somewhere there seems to be a level that coordinates this process, and as a speculation one might propose an access to the non-computable level at this point. This may look like an attempt to revive the idea of hidden variables, but it does not seek to make the wave function collapse consistent with classical physics or algorithmic determinism, the aspect of hidden variables that has been refuted.Tags: Travis Craddock, tryptophan Posted by