There are several reasons why awareness is unlikely to be the result of brain activity.

You can be aware of different external and internal phenomena, but awareness is the property of none of them. For example, you can become aware of a chair, but the chair does not possess awareness. By the same token, you can become aware of your body, thoughts or emotions, but your emotions, for instance, are neither aware of themselves nor of any other part of you. So, if awareness cannot be identified with any mental process,  it either resides in a discrete part of the brain or it is not in the brain at all. A part of the brain that is responsible for awareness (not sensations that provide the materials of awareness) has not been located. Considering the prominence of awareness, if it is not located by now, it is not likely to be located ever. True, waves of a certain frequency are present when we are aware, but they cannot be the source of awareness, otherwise a machine producing these waves should be aware too.

This, of course, poses a problem for materialists, so awareness is sometimes considered an emerging property of brain activity that is evenly distributed, and therefore cannot be distinguished from the ‘noise' (unspecified neuronal activity). However, if this is the case, awareness should be far less discriminatory. Yet, most of the processes in the brain do not trigger awareness, and there are no processes that we necessarily have to be aware of (including sensory, motor, cognitive and affective ones). You can have a sensation, but not be aware of it until you pay attention. For example, if you focus on your sitting in a chair, you will suddenly become aware of the sensations associated with sitting. Your nervous system has been processing these sensations all the time, but you have not been aware of them until you have turned attention to the sitting. This indicates that awareness does not automatically emerge from neuronal activity. On the basis of his own experiments, Libet concludes that awareness cannot be simply the result of brain complexity (as emergentists would like to believe):

Many, if not most, mental functions or events proceed without any reportable awareness... even complex functions, as in problem solving or intuitive and creative thinking. On the other hand, the simplest kind of mental functions can be accompanied by awareness/subjective experience, like awareness of a tap on the skin... It is not, then, simply the complexity or creativeness of a mental function that imparts to it the quality of subjective awareness of what is going on. The cerebral code for the distinction between the appearance or absence of awareness in any mental operation would seem to require a mediating neuronal mechanism uniquely related to awareness per se rather than to complexity, etc. (in Nunn, 1996, p.40)

The last sentence seems to suggest that a specific brain mechanism should be associated with awareness, but Libet was not able to identify any (besides duration of the stimuli). In fact, even duration and intensity do not always  correspond to awareness. One can become aware of the sensations transmitted through the nervous system or not, without any qualitative or quantitative changes in the activity of the nervous system (unless awareness triggers an intention or some other reaction). Moreover, experiments show that the threshold of awareness is lower after one has become aware of a sensation. If awareness and the brain process are identical, the relation between the intensity (or duration) of the stimuli and experience of a sensation should be fixed, and this does not seem to be the case.

Some empirical data also support the view that awareness is not a brain function.

Electrical stimulation of the cortex can initiate memory flashbacks so realistic that they are perceived as real experiences. This is sometimes taken as evidence in support of the materialistic view. However, the very neurosurgeon who conducted these experiments, Wilder Penfield, drew a very different conclusion. Patients are aware of both, being on an operating table and the triggered memories at the same time. Penfield reasons:

The fact that there should be no confusion in the conscious state suggests that although the content of consciousness depends in large measure on neural activity, awareness itself does not... If the brain mechanism is busy creating the mind by its own action, one might expect mental confusion when the neuronal record is activated by an electrode.  (1975, p.55)

Transpersonal experiences (e.g. dislocated or expanded awareness occurring sometimes in meditation) and some experiments in para-psychology that have produced small but statistically significant positive results under unusually stringent conditions[4], also point in the same direction - namely that awareness can exist beyond or independent of brain processes. To quote Penfield again:

After years of striving to explain the mind on the basis of brain-action alone, I have come to the conclusion that it is simpler (and far easier to be logical) if one adopts the hypothesis that our being does consist of two fundamental elements. (ibid., p.80)

If one of these two fundamental elements is not in the brain, it must be non-material.

  • [4]. For relatively recent reviews see Bem and Honorton (1994) and Schlitz and May (1998).