ULTIMATE COMPUTING - Quantum Consciousness Studies

Models of Cytoskeletal Computing 157
8 Models of Cytoskeletal Computing
Cooperative, collective effects of dynamic protein conformational states are a
likely substrate for biological intelligence ranging from cytoplasmic probing to
human consciousness. The activities, functions, and structures of microtubules
and other cytoskeletal components appear suited to information processing and
have led at least a dozen author groups to publish theoretical models of
rudimentary cognition within MT and the cytoskeleton. The concepts range from
passive MT signal transduction, to descriptive patterns among MT subunit states,
to dynamic cooperative “automaton” effects among coherent oscillations of
centrioles and the cytoskeleton, to cytoplasmic/cytoskeletal “sol-gel field” effects
utilizing holographic imagery. If correct, these proposals could explain many
aspects of information representation and dynamic organization in biological
systems. Hopeful metaphors, these models are non-exclusive and may be
overlapping and complementary.
Cytoskeletal information processing would require some mechanism of
cooperativity, long range order, coherence, and/or energy transfer among
cytoskeletal components and their subunits. Such possible mechanisms were
discussed in the previous chapter. Specific evidence which supports transfer of
energy and information within microtubules will be discussed here followed by
thirteen models of cytoskeletal information processing.
8.1 Energy and Information in Microtubules
Direct support for the propagation of signals in MT has been generated by
Vassilev, Kanazirska, and Tien (1985) who reconstituted bilayer membranes from
brain lipids and studied their electrical excitability. They suspended membranes
as parallel unconnected plane surfaces separated several millimeters apart in a
buffer solution which contained depolymerized tubulin, GTP, and other
physiological components. Each membrane was monitored electrically and
baseline recording of the two membranes showed no electrical coupling; when
one membrane was electrically stimulated it depolarized, but the other membrane
remained silent. When the tubulin was caused to polymerize into MT (by
lowering calcium ion concentration) MT bridges formed between the two
membranes and electrical coupling between the two membranes was observed.
Electrical stimulation of one membrane then resulted in depolarization in both
membranes. The addition of the MT destabilizing drug colchicine prevented
coupling, demonstrating that intact microtubules were necessary. The authors
concluded that intermembrane signaling occurred by electrically induced
polarization and conformational changes of MT components which linked the two
membranes. They suggested that similar communication functions occurred
routinely within the cytoskeleton.
Another series of experiments which supports the notion of MT mediated
signaling is fluorescence resonance transfer among MT and membrane
components. Becker, Oliver and Berlin (1975) developed a technique to study
energy transfer among fluorescent groups separately attached to different MT
subunits or to membranes. Resonance energy transfer occurs when a fluorescent
portion of a molecule (“chromophore”) which is electronically excited by the
absorption of light energy transmits that energy to another “acceptor”
chromophore some distance away. This transmission requires the overlap of the
emission spectrum of the “donor” chromophore with the absorption spectrum of
the acceptor, without involving the actual reabsorption of light by the acceptor.
The process is therefore referred to as “nonradiative” resonance energy transfer