ULTIMATE COMPUTING - Quantum Consciousness Studies

44 Brain/Mind/Computer
2.2.11 Cytoskeletal Basis of Consciousness
Figure 2.4: Interior of neuron showing cytoskeletal network. Straight cylinders are
microtubules, 25 nanometers in diameter. Branching interconnections are
microtrabecular lattice filaments. Neurofilaments are not shown. By Jamie
Bowman Hameroff.
Classical approaches to understanding the brain/mind have assumed a
hierarchy of organization in which interneuronal synapses are the indivisible
substrates of information transfer (Figure 2.2). However, neurons appear far too
complex to be simple digital switches or gates and must contain intrinsic
information processing systems.
The neuron is often and mistakenly described as a simple device that
compares a weighted sum of dendritic “analog” input signals with some threshold
level above which an output “digital” pulse is transmitted along an axon. The
structure of neurons, in which vast arborizations of dendritic fibers may accept
some 100,000 synaptic inputs per neuron, indicates a very complex system. While
some have viewed the dendritic tree as being a passive transmitter of impulses,
data suggest action potentials in large dendrites, slow depolarization waves in
others, and the possibility of elementary logic operations at branching points
(Scott, 1977). Each dendritic branch point may act as a logical “OR” gate if a
pulse on either daughter branch can supply sufficient charge to excite a pulse on
the parent; otherwise it may act as a logical “AND.” Dendrites may also be