A few weeks ago popular science news outlets ran a story about scientists claiming to crack the “brain memory code” (e.g. here and here). The article about this story was published in PLoS Computational Biology on the 8th of March 2012. Scientists have known for quite a while that calcium signaling plays an important role in long-term potentiation, a fancy way for saying the generation of memories. This study suggests that the calcium-calmodulin dependent kinase II (CaMKII) plays a role and it does so by interacting with microtubules. What are microtubules and what do they have to do with memory you may ask?
Well, the study was carried out Stuart Hameroff and his colleagues. Stuart Hamerhoff in conjunction with Roger Penrose has developed the "orchestrated objective reduction" or "Orch OR" model for consciousness and neural information processing. The basic idea is that there is a link between quantum superpositons and quantum decoherence, aromatic ring pi-bonds of some amino acids, intracellular protein formation, microtubules and neural activity and finally consciousness. This study on CaMKII just links memory formation to consciousness via microtubules in their model. Confused? Let's take one step at a time.
In order to understand what these scientists are suggesting, one needs to understand a few basics of their “Orch OR" model for consciousness.
The “quantum physics” and “aromatic ring pi bond” connection.
An aromatic (aromaticity) compound is composed of a conjugated planar ring system with delocalized pi electron clouds. Benzene is an example of an aromatic compound (Figure 1). In benzene and other aromatic compounds the double bonds are shorter than the single bonds, causing the carbon atoms to be pulled and pushed between two states and thus vibrate between two states (Figure 2).The pi electrons are also delocalized above and below the carbon ring (Figure 1). Aromatic compounds are thus described to be resonating between two states in a quantum mechanical manner.
The “aromatic ring pi bond” and “protein formation” connection.
Four amino acids contain aromatic rings: tyrosine, phenylalanine, tryptophan and histidine. Histidine, however has six delocalized electrons but not a benzene ring and is hydrophilic (more polar). When peptide chains fold to form proteins, the structure is stabilized and dynamically regulated in the intracellular aqueous phase. Polar side groups face outwardly and react with the polar aqueous milieu, while non-polar regions face inwardly (Protein folding). Aromatic amino acids are more non-polar and thus coalesce more readily in the centre of a protein. When aromatic amino acids coalesce it allows London force van der Waals interactions between the non-polar electron clouds of the aromatic rings, causing quantum resonation of the coalesced non-polar aromatic rings (Figure 3).
The “protein formation” and “microtubule” connection.
Microtubules are long, hollow, cylindrical, filamentous, tube-shaped protein polymers consisting of alpha and beta tubulin dimers and form part of the cytoskeleton (Figure 4, Figure 5, Figure 6). Microtubules play important roles in cell signaling, cell division and mitosis, vesicle and mitochondrial transport and play crucial roles in the development and maintenance of cells and cell shape. Microtubules can polymerize (rescue/elongate) at the positive (+) end and depolymerize (catastrophe/shorten) at the negative (-) end.
The “microtubule” and “consciousness” connection.
The model proposes that quantum level resonance as a result of quantum level dipole oscillations (London van der Waals forces) within hydrophobic pockets result in functional protein vibrations which depend on quantum effects such as superposition (Figure 7). The quantum effect on a single tubulin protein conformation is superimposed and exists in both states simultaneously and acts as a qubit or a aq uantum bit of information. (as in a quantum computer). Thus, the elegant formation of microtubules in neurons is postulated to form some sort of lattice of quantum resonating qubits and in theory constitute a quantum computer. Hamerhoff descibes how quantum decoherence and superposition in microtubules can be linked to consciousness in his papers “The “conscious pilot”—dendritic synchrony moves through the brain to mediate consciousness (Journal of Biological Physics) and “Lateral Information Processing by Spiking Neurons: A Theoretical Model of the Neural Correlate of Consciousness” (Computational Intelligence and Neuroscience). Hamerhoff together with Penrose also describe and defend the model in a bit more detail in their article “Consciousness in the Universe: Neuroscience, Quantum Space-Time Geometry and Orch OR Theory (penrose and Hamerhoff (2011)”.
There are interesting philosophical consequences. Firstly, if it is true that quantum superposition and decoherence in microtubules play a role in consciousness, and microtubules act as information processing units, then we will have to wait a bit longer for the supposed singularity that is projected if Moore’s Law is followed.
Secondly, if quantum superposition and decoherence and Hamerhoff and Penrose’s model is correct then some form of panpsychism or panproto-experientialism may be true. Consciousness on this view is a foundational, irreducible component of reality. Or as Hamerhoff states it “Consciousness or its ‘proto-conscious’ precursors are thus somehow built into the structure of the universe—a view that we might label pan-protopsychism” and “Consciousness is a sequence of transitions, of ripples in fundamental spacetime geometry, connected to the brain through Orch OR”. Some call it materialism on steroids, other call it a form of idealism.
Say whatever you want about the theory, it certainly is interesting. Whenever a scientist of Penrose’s caliber endorses something then it is probably worth looking into even if you ultimately do not find it or its philosophical implications convincing.