My review of the Ego Tunnel:

Nice discussion of Metzinger's theory of consciousness. His basic claim is that what humans tend to think of as a "self" is what he calls a "phenomenal self-model" (PSM). As the name suggests, the PSM is the brain's model of the organism as a whole, and includes things such as a model of the organism's body. The PSM is situated within a broader world-model of the environment that the organism exists in. Metzinger claims that the reason why we experience there being thing such as "selves" is that there has been no evolutionary advantage in seeing the PSM as a model - we do not see the sophisticated computational machinery which produces it, and thus experience it as something self-contained and essential, rather as something that's constructed from parts for the sake of enabling better information-processing.

Metzinger's book discusses a number of experiments as well as details of what our conscious experience is like and what the reasons for that might be.

For example, humans perceive time as a kind of eternal present: everything we experience is experienced as happening "now", and even when we recall a memory of the past or think of the future, it is experienced as us remembering or planning something right now. But one could imagine a mind that didn't have any conception of an immediate privileged now. Metzinger doesn't go into detail of how this kind of a different mind would represent time, but personally I could speculate it as having just mental representations of events with different timestamps, with increasingly broad probability distributions on those events that had not yet been witnessed but which were extrapolated to happen, or of which sufficient time had passed that the memories might be becoming uncertain...

Metzinger suggests that the experience of a unified now emerges from the need to take quick action in response to threatening situations in the environment, and to provide all of the subsystems in the brain with a shared temporal frame of reference:

Although, strictly speaking, no such thing as Now exists in the outside world, it proved adaptive to organize the inner model of the world around such a Now - creating a common temporal frame of reference for all the mechanisms in the brain so that they can access the same information at the same time. A certain point in time had to be represented in a privileged manner in order to be flagged as reality.

Metzinger also suggests that this sense of a Now is part of what enables consciousness as we understand it: experiencing ourselves as being embedded in a constantly-developing Now is a fundamental part of human experience and consciousness.

The weakest part of the book is the last third, where the topic suddenly switches into that of ethics. The discussion in this section seems quite disconnected from that of the previous sections, and Metzinger starts talking about issues such as national drug policies and whether meditation should be taught in schools. A part of this discussion is justifiable as it touches upon the question of the effects that an increased understanding of consciousness research will have on society, but the whole discussion mostly comes off as superficial and not very well-argued. (Though I will admit that I started skimming this section pretty quickly.)

Nonetheless, overall Metzinger paints a very interesting picture of his theory of how the brain might work, though there's still a definite speculative vibe around it all.