Neuroscientists who work on the human brain seldom mention free will. Most consider it a subject better left, at least for the time being, to philosophers. Meanwhile, their sights are set on discovering the physical basis of consciousness, of which free will is a part. No scientific quest is more important to humanity. Everyone — scientists, philosophers, and religious believers alike — can agree with the neurobiologist Gerald Edelman that “[c]onsciousness is the guarantor of all we hold human and precious. Its permanent loss is considered equivalent to death, even if the body persists in its vital signs.”
The physical basis of consciousness won’t be an easy phenomenon to grasp. The human brain is the most complex system, either organic or inorganic, known in the universe. Each of the billions of nerve cells (neurons) composing its functional part forms synapses and communicates with an average of ten thousand others; each launches messages along its own axon pathway using an individual digital code of membrane-firing patterns. The brain is organized into regions, nuclei, and staging centers that divide functions among them. These regions respond in different ways to hormones and sensory stimuli originating from outside the brain, while sensory and motor neurons all over the body communicate so intimately with the brain as to be virtually a part of it.