Because of its variety of purposes the book is quite uneven and always surprising, and that is a good thing, on both counts. I bought it because I wanted to know about the neurobiology stuff. Here was one of the world's leading scientists in the field of consciousness setting out his insights in a form accessible to those who cant read all the peer reviewed journals. He does this wonderfully, and it is all interspersed with enough of the autobiographical stuff to help me grasp the meta story: what drives a man to study this stuff and what does studying it do to him? In terms of pure science of course, these questions are crashingly irrelevant, but given the subject matter, they do seem important to me.
Koch's starting point is what philosophers sometimes call "the Hard Question"; i.e. the mind/body question. That is, how can immaterial things have an effect on material things? How can something as ephemeral and abstract as my thought - "I will go to the shop and buy a Time Magazine" - convert itself into real, measurable phenomena in the material world - movements in my muscles, the movement of a ton of metal down the road, the transfer of cash, the transport of some printed paper. A related question is the nature of consciousness: what is this "I" that is capable of deciding whether or not to buy a magazine? Koch's response to these questions has been a lifetime spent at the forefront of neuroscience investigating the structure and function of the brain. Influenced by thinking in information theory, he is convinced that consciousness is a function of systems that are both complex and integrated. The more complex a system is, and the more its various component parts are integrated with each other, the more it will be sentient. That is, the more consciousness it will possess. The human brain is enormously complex and each of its component parts is connected with each of the others in manifold ways, so the human brain is conscious. Stop some of that integration, and the complex brain will stop being conscious, as happens in anaesthesia or deep sleep. Other brains are less complex and less integrated but will nevertheless possess enough complexity to be conscious at some level. As will perhaps some artificial systems.
The argument is carefully laid out, exhaustively backed up with experimental evidence and quite compelling. Quite compelling, but only quite. In the end I'm not sure that the hard question has been answered. Koch has come a long way from Descartes theorising that the soul was housed in the pineal gland, but in the final analysis, I'm not sure his answer is qualitatively any different from Descartes' even though he has quantitatively more data to back himself with. Koch locates consciousness not in one part of the brain but in the brain as a whole but still cannot say how the abstractions of though give rise to material action in the physical world. He makes a case for the rise of consciousness as an evolutionary requirement; that is, it bestows a survival advantage on species to be able to plan and decide, but I don't find this very convincing because of the unconscious mind. The unconscious also seems to reside in the complex and integrated brain, and to have powers of perception and the ability to make decisions; and yet it is... unconscious. Why should evolution not favour increasingly sophisticated zombies over consciousness beings?
But more than this, I find Koch's idea of consciousness to be too static. He has a formula which calculates the level of consciousness according to the complexity and level of integration of a system, but this seems to me to reduce consciousness to a stable, calculable property, when in fact it is a process. And more, it is a process which grows and develops in sophistication over time, even when it is being borne in a system (the human brain) or more or less constant levels of C&I. Koch seems to miss the point of all the great world faiths: they are not systems of belief so much as methods of analysing and promoting the development of consciousness which proceeds in a fairly predictable pattern.
Koch ends the book regretting the loss of his childhood Catholicism with its comforts and sureties, but he is unable to believe because of his inability to reconcile an immaterial deity with action in the material world. And yet he can only explain the existence of the universe by positing that "some deep and elemental organising principle created the universe and set it in motion for a purpose I cannot comprehend". So this principle created a universe in, presumably, a similar manner to the way my desire creates movement in my legs and the progression of my car towards the shop. We seem to be back where we started from.