Anatomy of Awareness

Awareness implies that the individual is not only alert but is cognizant of self and surroundings. Interaction of the cerebral cortex and the reticular system is required for the individual to be aware. Analysis of patients in the vegetative state and the study of anencephalic infants provide a picture of reticular system function in the absence of the cerebral cortex. The opposite problem, that of understanding the function of the cortex in the absence of reticular system control, is difficult to study. First, almost all lesions damaging the midbrain or thalamic reticular structures also impair motor output, and second, although the cortex appears electroencephalographically to be idling, there is no electrical technique by which one can determine whether the cortex is aware. A few case reports suggest that olfactory stimulation (which does not require transit through the midbrain or thalamus to reach the cortex) may produce an EEG change, and patients in alpha coma due to a midbrain lesion will rarely alter this EEG pattern. These are the only suggestions that external stimuli can alter cortical function in the absence of reticular system driving. With current techniques, scientists are not able to examine whether the cortex of an individual with a reticular system lesion is able to perceive any internal state (e.g., hunger).

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