In the 1960s the US neurophysiologist Benjamin Libet discovered that the "readiness potential" precedes movement by about half a second, and awareness of this "decision to act" follows by about 300 milliseconds. In other words, the brain decides unconsciously to act, before we are aware of having decided to act. We become aware of the action only if the neural event lasts about 500 milliseconds.

A way to interpret this is that we are conscious only of electric field patterns in the brain that last about half a second. The scary notion, of course, is that a) we are not conscious of many "decisions" that our brain makes (anything that occurs in less than half a second) and we are conscious of "our" decisions only "after" the brain has already decided them. This can be interpreted as proof that free will is an illusion, or that free will has about 200 milliseconds to "veto" what the brain wants to do.

Nunez interprets Libet's experiments as showing that a) it takes about half a second to become aware of something because that awareness is due to some global brain activity with a lot of loops; and b) the conscious and the unconscious are in continuous communication, a feedback loop of its own.

One can visualize Nunez's theory as a team that needs to reach a group decision. Several individuals exchange information on what each knows about what is going on and collectively try to agree on a unified view of what is going on. One individual offers an interpretation based on what she saw or heard; another one objects that this is not consistent with what he saw or heard, and offers an alternative explanation; another one jumps in with yet another piece of information that contradicts both opinions and then she offers a third hypothesis of what is going on; and then the first one shows that this is still not consistent with what she knows, and offers another possible explanations; and so on. When they finally agree on what went on, they issue a press release that they all agree with. This discussion and negotiation, of course, takes time. Hence the delay in becoming aware (i.e, in issuing the press release).

Nunez thinks that consciousness is due to the elaborate interaction of many subsystem. He builds his case methodically. Nunez focuses on a particular class of neurotransmitters, the "neuromodulators" (dopamine, serotonin, acetylcholine, etc), spread through large areas of the brain and are crucial to determine the large-scale dynamics of the cortex; and Nunez emphasizes that "the cortex has a fractal-like structure and exhibits fractal-like dynamic patterns".

He shows that what makes the human brain special, compared with the brains of other mammals, is the relative preponderance of corticocortical fibers (cortex to cortex connections) over thalamocortical fibers (cortex to thalamus connections); which is the exact opposite of what happens in the brains of other mammals.

It has become fashionable to explain how consciousness emerges from the brain by invoking the emergent properties of complex adaptive systems. The problem is that the brain is not the only complex adaptive system inside the human body. The eye, the heart, the stomach and pretty much every other organ are complex and adaptive too, but they don't seem to have much to do with consciousness, not even a faint one. The property of complexity alone does not explain consciousness. The question is what makes the complex system of the brain different from the complex system of any other bodily organ.

Paul Nunez emphasizes the cortex's nested hierarchical structure ("neurons within minicolumns within modules within macroculumns inside cerebral cortex lobes"), a model pioneered in the 1970s by the US physicist, philosopher and neurobiologist Walter Freeman.

That might be the unique feature of the brain, but, to some extent, many other bodily organs and natural systems exhibit a "nested hierarchical" organization: are they conscious too? It seems odd that consciousness is a zero or one: the highly nested hierarchical complexity of the brain yields my consciousness, while the less nested hierarchical complexity of the heart yields absolutely no consciousness.

It would be more logical to find a continuum of contributions to my consciousness by all the complex organs of my body all the way down to fingertips and hairs. Consciousness should be distributed all over the body, to different degrees. For example, any muscle is a complex adaptive system that learns from experience.

To expand on Freeman's studies, Nunez, who has a background in electrical engineering, delves into signal analysis. A sine wave (or sinusoidal oscillation) is determined by three features: amplitude (the energy of each cycle, the difference between crest and rest), frequency (the number of cycles per second, which, given the velocity of propagation, also determines the wavelength, i.e. the distance from crest to crest) and phase. Signals are synchronous when they have the same phase (each cycle of the wave begins and ends at the same time). Coherence measures the phase consistency between two signals. Coherence is one, for example, when the two signals are perfectly synchronous.

A signal is generally a combination of several frequencies, each with its own amplitude and phase. The fast Fourier transform is the mathematical technique that separates the various frequency components of a signal. A signal can be synchronous/coherent with another signal at some frequency but not at others. Traditionally, the electroencephalogram measures large-scale electrical activity in the brain. Depending on the mental and bodily state, the "signal" picked up by an electroencephalogram contains different frequencies. When the local electrical activity is measured, instead, local differences become evident.

The alpha, beta, delta, theta and gamma brain waves are the result of measurements of temporal patterns. Spatial analysis (locating the source or the distribution of a "wave") has traditionally been more difficult.

Nunez shows that, in general, dynamic processes can be coherent in one frequency band while being incoherent in another band; which, in particular, means that two cortical groups can be highly coherent (i.e. strongly correlated) at one frequency while being weakly coherent (i.e. weakly correlated) at another frequency. "Distinct neural groups can be bound by resonance in some frequency bands while, at the same time, operating independently at other frequencies". Resonance is the capacity of systems to respond selectively to stimuli in narrow frequency bands. Television sets and radio sets allow the viewer/listener to pick the resonant frequency (i.e. the broadcast).

Once that is done, the tv set responds only to inputs (i.e. shows only the broadcasts) at that frequency. A general property of oscillators is that weakly coupled oscillators can interact strongly when they produce appropriate resonant frequencies. The US biophysicist Bill Baird had already shown how oscillatory neural networks can account for pattern formation and recognition ("Nonlinear dynamics of pattern formation and pattern recognition in the rabbit olfactory bulb", 1986).

The synchronization of oscillating networks was then the object of the research by the US mathematicians Frank Hoppensteadt and Eugene Izhikevich ("Synaptic organizations and dynamical properties of weakly connected neural oscillators", 1996).

Nunez synthesizes these studies as showing that neural groups can use rhythmic activity to communicate selectively even to groups to which they are not directly connected. This discussion about synchronized oscillators is important because spatial correlation patterns are associated with mental tasks. It means that neural groups that are not adjacent can collaborate in performing a mental task.

Brain regions are functionally isolated at some frequencies while being functionally integrated at some other frequencies. Hence the "binding" that yields consciousness takes place both in space and in time. Consciousness is due to both local and nonlocal connections.

In parallel, Nunez argues that local neural phenomena coexist with global ones. In general, complex adaptive systems (such as the brain) can operate over a broad range of isolation or integration. At one extreme there is functional isolation of the subsystems; at the other extreme there is global coherence. The brain, therefore, is both a set of subsystems with minimal communication (when it operates in "functional isolation" mode) and a whole that is globally coherent.

Nunez calls his model a model of "neural networks embedded in global fields". Neurotransmitters can move the brain along that continuum, from granular assembly of functionally isolated subsystems to highly integrated globally coherent whole. In fact, Nunez thinks that a balanced mental state is a balanced compromise between the two extremes; and that mental diseases can be explained as overcorrelated or undercorrelated states.

Nunez notes that when one undergoes anesthesia (i.e. when "thinking" is vastly reduced), local differences tend to disappear. His interpretation is that the transition from intense mental activity to minimal mental activity corresponds to a transition from local to global neural activity.

Overall, i don't think that Nunez has come any closer to proving that consciousness is due to the nested hierarchical structure of the brain. I see no new evidence about this old claim. In fact, the more details from neurophysiology the less credible this theory appears in logical terms.

The first eight chapters of this book are written in a rather technical style, with many detailed explanations of neurological experiments (and even more detailed ones in the appendix). Some chapters requires tolerance for technical jargon. Each chapter has a summary, but some of these summaries sound too much like abstracts of technical papers published in specialized magazines. At the same time, Nunez likes to take detours into politics, science fiction and even poker that, personally, i didn't find very useful.

The last four chapters abandon the technicalities and delve into philosophical speculation (three of them are actually just introductions to the ideas of modern Physics). Nunez believes consciousness, and the general functioning of brains, cannot be fully understood without acknowledging the structure of nature revealed by modern Physics, namely Relativity, Quantum Physics and Thermodynamics, three disciplines that happen to pose limitations on the speed, amount of quality of information that can be transmitted in a physical process.

I find his definitions of ultra-information ("that which distinguishes one entity from another") and ultra-computers not very useful to discuss the nature of consciousness. Here he is influenced by US physicist Seth Lloyd, author of the seminal PhD thesis "Black Holes, Demons and the Loss of Coherence" (1988) and of the popular-science book "Programming the Universe" (2006), who considers information as a fundamental property of the universe. And i don't quite understand how his cortical field theory would be consistent with Bohm's implicate and explicate orders.

Nunez speculates that a social consciousness may emerge from a number of socializing minds if they get closely interconnected the way a brain's subsystems are. This "room-scale consciousness" must have been thrown into the book just to fire up the imagination of those inclined to believe in hippie-style super-consciousness.

Talking of which, Nunez leaves the door open to the universal consciousness, of which our individual selves might be just limited instantiations. But the important point that he makes in this last chapter is that whatever accounts for consciousness may come from multiple spatial scales: the quantum, the molecular, the electrical and, who knows, some still unknown field out there.