Jim Beran's Abstract for Toward a Science of Consciousness 2012, Tucson, Arizona

Title:

Taking Hints from Protozoans--Did Microtubule-Related Plasticity Evolve Jointly with Consciousness?

Abstract:

If microtubules and other cytoskeletal components are involved centrally in consciousness, one would expect evolutionary and developmental changes in consciousness to correspond somehow with changes in cytoskeleton. (Compare, e.g., Arhem et al. (2008)) The literature provides several relevant studies--e.g. about evolution of cytoskeleton itself (See Erickson (2007) etc.), tubulin (See, e.g., Tuszynski et al. (2006)), microtubule associated proteins (MAPs) (See, e.g., Dehmelt et al. (2004)), synapses (See Emes et al. (2011) etc.)--but we find no persuasive description of correspondence between changes in conscious experience and changes in cytoskeleton based on mutation and/or expression of genes. Indeed, each day's new, unique conscious experiences could not possibly result from corresponding genetic mutation--human evolution couldn't happen overnight.

Trying a different tack, we find hints that evolution led from earlier unicellular organisms lacking microtubules to a wide variety of protozoans and other protists with extraordinarily diverse microtubule-containing cytoskeletons (See Gull (2001) etc.); from one such protist, the path apparently led to complex animals with microtubule-rich neurons (See Baas et al. (2009) etc.) in brains capable of changing among a broad repertoire of conscious experiences. Neuroscientists accept, of course, cytoskeleton's generic role in constructing and operating neural circuits (See Purves et al. (2008) etc.), including neural circuits involved in consciousness; but the evolutionary path from protozoans to animals with brains suggests that cytoskeleton also evolved features specifically involved in consciousness. To explore this possibility, we make three working assumptions: (1) Microtubules and other cytoskeletal and synaptic components can interact in concert with changes in conscious experience--we call their concerted interactions "real-time plasticity" or "RTP"; (2) in response to each distinct source of neural signals that change conscious experience, neurons in a respective neural circuit undergo RTP and thus transduce the neural signals into changes in conscious experience, i.e. performing neural-to-conscious transduction ("N-to-C transduction"); and (3) an N-to-C transducer circuit obeys a relatively stable (though perhaps probabilistic and context-dependent) mapping from neural signals to changes in conscious experience. (For related concepts, see Hameroff (2006) re "real-time activity"; Woolf et al. (2009) re "collective plasticity"; etc.)

These assumptions suggest that mutations of more than one type occurred during joint evolution of cytoskeletal plasticity and consciousness--examples include, first, cytoskeleton-affecting mutations that support RTP in N-to-C transducer circuits ("Cyto-RTP mutations") and, second, mutations, e.g. in sense organ proteins, that affect neural inputs to Cyto-RTP-based transducer circuits ("neural input mutations"). To illustrate interplay between different types of mutations, we develop hypothetical accounts of two visual phenomena: In one, trichromatic vision occurs immediately when necessary photopigments are first expressed (See Mancuso et al. (2010) etc.); in another, experiences of reading can arise either through visual or tactile sensation. (See Cheung et al. (2009) etc.) If we can identify Cyto-RTP mutations and neural input mutations that have related effects on visual or other phenomena, we will have much stronger evidence that cytoskeleton has features specifically involved in consciousness.