Neuronal Man: The Biology of Mind
by Jean-Pierre Changeux (Pantheon: $19.95; 284 pp., illustrated)
In 1738, Jacques de Vaucanson, the inventor of the automatic loom, demonstrated his "digesting duck." Designed with the help of a surgeon named Claude Le Cat, the duck could flap its wings, swallow, digest grain and excrete the residue. Vaucanson's duck vividly illustrated that life functions can proceed without a special life force.
But what about such higher processes as thought and emotion? Does the human spirit have a special place in, or outside of, biology?
Jean-Pierre Changeux argues that humanity no longer has a need for "spirit." It is enough, he says, to be "Neuronal Man." Changeux wants to destroy the barriers that separate the mental from the neural. Aware of the immensity of this enterprise, he begins by placing "a ladder against the wall of this mental Bastille." Changeux's book is a long epitaph for the dualism of Descartes.
"There is no virgin forest," wrote the poet Paul Valery, "no clump of seaweed, no maze, no cellular labyrinth that is richer in connections than the domain of the mind." Changeux equates mind with brain and engagingly explores the labyrinths of the latter. He traces neurological understanding back 5,000 years to the writing of an anonymous Egyptian surgeon who noted with surprise that wounds to the head could impair movement and speech.
Neurobiology, like biology in general, has sought to identify function with specific structures. Despite the continuing fantasy that the heart is the site of the soul, Galen had already in the 2nd Century begun to localize within the brain such faculties as the control of motor activity, sensation and thought. "Do not consult the gods to discover the directing soul," Galen admonished, "but consult an anatomist."
Changeux traces the history of brain science as it examined first the functions of individual regions of the brain and then of individual nerve cells, or neurons. He explains how neurons use their component molecules to communicate chemically and electrically, a subject into which his own research has provided major insight. His chapter, "Animal Spirits," fittingly ends with a picture and a discussion of a molecule that has occupied his laboratory for the last years, the receptor for the neurotransmitter acetylcholine.
Changeux recognizes the limitations of pure reductionism. The operations of transmitters, ions and modulators, of molecular pumps, gates and channels, do not by themselves explain action, thought or affect. The question is whether higher functions "emerge" from the properties of component molecules and cells, or whether they demand new rules or forces. For Changeux, no new rules are necessary, and the middle section of "Neuronal Man" suggests how networks of neurons can accomplish what many philosophers have attributed to mind, spirit or soul.
Changeux shrinks from no challenge, as a listing of some of his topics attests: "to sing and to flee," "to drink and to suffer," "to enjoy and to be angry," "to reach orgasm," "to analyze," "to speak and to do," "the materiality of mental images," "problems of consciousness," "the calculation of emotion" and "the substance of the spirit."
These discussions are well informed and strongly argued. Changeux uses recent advances in neuroscience to contend not only with traditional theology but also, among others, with Bergson, Pavlov and Freud. He views the conscious brain as a "comparator," which continually checks "mental objects" against reality. In dreams, delirium and hallucinations, the comparator fails, but the nature of these failures supports his conviction that mental objects indeed have concrete existence in the brain.
The "dreams" of cats provide an intriguing example. As in humans, the sleep of animals is punctuated by storms of electrical activity in the brain--called rapid eye movement or REM sleep. This electrical activity does not cause movement because of the inhibitory action of a group of neurons in the brain stem. Destroying these paralyzing neurons results in animals that move even as they sleep. Changeux tells of such a sleeping cat that explored its territory, licked itself, attacked an imaginary mouse, and showed signs of anger. He speculates that during REM sleep, the brain evokes mental objects and links them together, albeit in the form of disorganized behavioral collages.
Consciousness, Changeux argues, consists of measuring mental objects and behavioral patterns against reality. This capacity is compromised in sleep, distress or insanity. "Madness," said Moreau de Tours, is "the dream of the waking man."