Self Comes to Mind

involved in these operations. An analysis of brain-stem neuroanatomy reveals several sectors of nuclei. The sector located at the bottom of the stem’s vertical axis, largely in the medulla oblongata, contains the nuclei that are concerned with basic visceral regulation, notably breathing and cardiac function. Substantial destruction of these nuclei spells death. Above that level, in the pons and in the mesencephalon, we find the nuclei whose damage has been associated with coma and vegetative state rather than death. Roughly, this is the sector that runs vertically from the midlevel of the pons to the top of the mesencephalon; it occupies the back part of the stem rather than the front, behind a vertical line that separates the back half of the brain stem from the front. Two more structures are also part of the brain stem: the tectum and the hypothalamus. The tectum is the ensemble made by the superior and inferior colliculi that we discussed in Chapter 3 ; architecturally, it provides a sort of roof at the top and at the back of the brain stem. Besides their role in movement related to perception, the colliculi play a role in the coordination and integration of images. The hypothalamus is located immediately above the brain stem, but its deep involvement in life regulation and intricate interactions with brain-stem nuclei justify its inclusion in the brain-stem family. We already addressed the role of the hypothalamus when we dealt with wakefulness in Chapter 8 (please refer to Figure 8.3 ).
    The idea that certain sectors of the stem would be critical for consciousness, but others would not, came from a classical observation made by two distinguished neurologists, Fred Plum and Jerome Posner. They believed that only damage located above the level of the midpons was associated with coma and vegetative state. 1 I turned the idea into a specific hypothesis by proposing a reason for this level setting: when we consider the brain stem from the perspective of brain regions located higher up in the nervous system, we discover that only above the level of the midpons does the collecting of whole-body information become complete. At lower levels of the brain stem or spinal cord, the nervous system can avail itself only of partial information about the body. This is because the midpons level is the level at which the trigeminal nerve penetrates the brain stem, bringing with it information about the top sector of the body—face and everything behind it, scalp, cranium, and meninges. Only above this level does the brain possess all the information it needs to create comprehensive maps of the whole body and, within such maps, generate the representation of the relatively invariant aspects of the interior that help define the protoself. Below that level the brain has not yet collected all the signals it needs to create a moment-to-moment representation of the entire body.
    This hypothesis was tested in a study that Josef Parvizi and I conducted in comatose patients aimed at investigating the location of their brain damage using magnetic resonance. It revealed that coma was associated only with damage above the trigeminal level entry. The study entirely supported Plum and Posner’s early observation, which had been based on postmortem material in the age before brain imaging was available. 2
    Early in the history of consciousness research, the association between damage to this region and coma/vegetative state was taken to mean that the resulting dysfunction disrupted wakefulness or vigilance. The cerebral cortex was no longer energized and made active. Deprived of its wakefulness component, the mind was no longer conscious. The identification of a network of locally interactive neurons that projected upward, as a unit, toward the thalamus and cerebral cortex made this simple idea all the more plausible. Even the name given to this system of projections—the ascending reticular activating system, or ARAS—captured the notion successfully. 3 (Again, please refer to Figure 8.3 . In Figure 8.3 the ARAS is contained within “other brain-stem nuclei,” as noted in the legend.)
    The existence of such a system has been thoroughly confirmed, and we know that its projections are aimed at the intralaminar nuclei of the thalamus, which in turn project to the cerebral cortices, including the PMCs. But this is not the whole story. In parallel with classical nuclei such as the cuneiform and pontis oralis, which are where the ARAS