Through neuronal avalanches to consciousness: Conjectures and elaborations

The concept of the conduction avalanche as a mechanism of signal propagation in the central nervous system was introduced in 1895 by Santiago Ramon y Cajal. Through such a mechanism, stimuli received by sensory receptor cells would be augmented as they reached the cerebral cortex through the corresponding anatomical pathways, leading to conscious perception. Cajal applied the concept to the visual, auditory, olfactory and somatosensory systems, and in 1896 extended it to the cerebellar cortex. Beginning in 1899 and up to 2003, prominent neuroscientists, including Lewellys F. Barker, C. Judson Herrick, Francis X. Dercum, Rafael Lorente de No, Cornelius U. Ariens Kappers, Hartwig Kuhlenbeck, Gordon M. Shepherd, and Rodolfo Llinas, have referred in their writings to the principle of conduction avalanches, crediting Cajal. In 2003, John Beggs and Dietmar Plenz introduced the concept of the neuronal avalanche, modelled after the power law of physics, as a property of neocortical networks and a new mode of spontaneous activity, distinct from the oscillatory, synchronized and wave states previously conceived to underpin the integrative function of the cerebral cortex. The topic has become an issue of intensive research over the past 15 years. In this paper, we discuss the basic tenets of the Cajalian principle, followed by an exposition of ideas throughout the 20th century, and an overview, in a modern perspective, of the neuronal avalanche as a mechanism in the current study of the neural bases of consciousness.