 Eccles called the fundamental neural units of the cerebral cortex ""dendrons"", which are cylindrical bundles of neurons arranged vertically in the six outer layers or laminae of the cortex, each cylinder being about 60 micrometres in diameter.Eccles proposed that each of the 40 million dendrons is linked with a mental unit, or ""psychon"", representing a unitary conscious experience.In willed actions and thought, psychons act on dendrons and, for a moment, increase the probability of the firing of selected neurons through quantum tunneling effect in synaptic exocytosis, while in perception the reverse process takes place.