The Mystery of Consciousness

The Astonishing Hypothesis: The Scientific Search for the Soul

by Francis Crick
Touchstone/Simon and Schuster, 317 pp., $14.00 (paper)

Consciousness Explained

by Daniel C. Dennett
Back Bay/Little, Brown, 511 pp., $15.95 (paper)

The Remembered Present: A Biological Theory of Consciousness

by Gerald Edelman
BasicBooks, 384 pp., $35.00

Shadows of the Mind: A Search for the Missing Science of Consciousness

by Roger Penrose
Oxford University Press, 457 pp., $25.00


The most important problem in the biological sciences is one that until quite recently many scientists did not regard as a suitable subject for scientific investigation at all. It is this: How exactly do neurobiological processes in the brain cause consciousness? The enormous variety of stimuli that affect us—for example, when we taste wine, look at the sky, smell a rose, listen to a concert—trigger sequences of neuro-biological processes that eventually cause unified, well-ordered, coherent, inner, subjective states of awareness or sentience. Now what exactly happens between the assault of the stimuli on our receptors and the experience of consciousness, and how exactly do the intermediate processes cause the conscious states?

The problem, moreover, is not just about the perceptual cases I have mentioned, but includes the experiences of voluntary actions, as well as such inner processes as worrying about income taxes or trying to remember your mother-in-law’s phone number. It is an amazing fact that everything in our conscious life, from feeling pains, tickles, and itches to—pick your favorite—feeling the angst of postindustrial man under late capitalism or experiencing the ecstasy of skiing in deep powder—is caused by brain processes. As far as we know the relevant processes take place at the micro levels of synapses, neurons, neuron columns, and cell assemblies. All of our conscious life is caused by these lower-level processes, but we have only the foggiest idea of how it all works.

Well, you might ask, why don’t the relevant specialists get on with it and figure out how it works? Why should it be any harder than finding out the causes of cancer? But there are a number of special features that make the problems raised by brain sciences even harder to solve. Some of the difficulties are practical: by current estimate, the human brain has over 100 billion neurons, and each neuron has synaptic connections with other neurons ranging in number from a few hundred to many tens of thousands. All of this enormously complex structure is massed together in a space smaller than a soccer ball. Furthermore, it is hard to work on the micro elements in the brain without damaging them or killing the organism. In addition to the practical difficulties there are several philosophical and theoretical obstacles and confusions that make it hard to pose and answer the right questions. For example, the common-sense way in which I have just posed the question “How do brain processes cause consciousness?” is already philosophically loaded. Many philosophers and even some scientists think that the relation cannot be causal, because a causal relation between brain and consciousness seems to them to imply some version of dualism of brain and consciousness, which they want to reject on other grounds.

From the time of the ancient Greeks up to the latest computational models of cognition, the entire subject of consciousness, and of its relation to the brain, has been something of a mess, and at least some of the mistakes in the history of…

This article is available to online subscribers only.
Please choose from one of the options below to access this article:

Print Premium Subscription — $99.95

Purchase a print premium subscription (20 issues per year) and also receive online access to all content on

Online Subscription — $69.00

Purchase an Online Edition subscription and receive full access to all articles published by the Review since 1963.

One-Week Access — $4.99

Purchase a trial Online Edition subscription and receive unlimited access for one week to all the content on

If you already have one of these subscriptions, please be sure you are logged in to your account. If you subscribe to the print edition, you may also need to link your web site account to your print subscription. Click here to link your account services.