Only actively moving creatures evolved a nervous system. So, the evolution of consciousness might have resulted from the brain internalising movement.[i] The process of internalisation can be seen in shark embryos, which undulate rhythmically inside the egg to ensure the even distribution of oxygen necessary for tissue development. At this stage of development, the movement is generated solely by the muscle cells, which have not yet been innervated by motoneurons. When the motoneurons migrate from the spinal cord to the muscles, the electrotonic coupling of muscle cells ceases, so that the brain can take control of motricity. Then the motility properties of the muscles become embedded into the neuronal circuits of the spinal cord, where they are integrated into the vestibular system, which monitors the effects of inertia acting on the organism through gravity and momentum.
Rhythmic movement is coordinated by central pattern generators, which alter the interneuronal pathways.[ii] Simply visualising a motor skill can modify the neural substrates for its physical performance.[iii] Mental practice is encoded into the neural networks, strengthening the same activation patterns triggered by the physical training. Visualisation is frequently used by performers to hone their skills. Even muscle strength increases, i.e. without the physical activity you would think was necessary for muscle growth.[iv] This undermines the notion of a metaphysical plane of consciousness, suggesting instead that the mind has evolved out of the structural coherence of consciousness and physiology.
Next chapter: Morphogenesis.
[i] Llinas, R.R. (2001). I of the vortex: From neurons to self. A Bradford Book, MIT Press, p.18.
“The nervous system has evolved to provide a plan, one composed of goal-oriented, mostly short-lived predictions, verified by moment-to-moment sensory input. This allows a creature to move actively in a direction according to an internal reckoning-a transient sensorimotor image-of what may be outside.”
[ii] Zehr, E.P. (2005). Neural control of rhythmic human movement: the Common Core Hypothesis. Exercise and Sport Sciences Reviews, 33 (1), p.56.
“Extensive reorganization of neuronal circuits involved in the generation of many rhythmic motor patterns (e.g. chewing, gastric mill, pylorus, etc.) has been well documented, and is altered extensively by various neuromodulators. That is, neuromodulators alter the activation and synaptic efficacy in various interneuronal pathways, and allow for the expression of different motor patterns with essentially the same neurons.”
[iii] Pascual-Leone, A., Nguyet, D., Cohen, L.G., Brasil-Neto, J.P., Cammarota, A. & Hallett, M. (1995). Modulation of muscle responses evoked by transcranial magnetic stimulation during the acquisition of new fine motor skills. Journal of Neurophysiology, 74, p.1043.
“Therefore, mental stimulation of movements activates some of the same central neural structures required for the performance of the actual movements. In doing so, mental practice alone seems to be sufficient to promote the modulation of neural circuits involved in the early stages of motor skill learning.”
[iv] Ranganathan, V.K., Siemionowa, V., Liu J.Z., Sahgal, V. & Yue, G.H. (2004). From mental power to muscle power—gaining strength by using the mind. Neuropsychologia, 42, p.953.
“The key findings of this study were that mental training increases voluntary strength of both distal and proximal muscles of human upper extremities and the strength improvements accompanied elevations of time-locked (to MVC trials) cortical potential (MRCP). Based on the MRCP data, we are confident that the primary mechanism underlying the strength increase is a mental training-induced enhancement in the central command to muscle. The data suggest that repetitive mental attempts to maximal muscle activation trained and enabled the brain to generate stronger signals to muscle.”