ental observations. The failure of introspection to reveal consistent laws led to the rejection of all mental states as proper subjects of scientific study. In behaviorist psychology, derived primarily from work of the American psychologist John B. Watson in the early 1900s, the concept of consciousness was irrelevant to the objective investigation of human behavior and was doctrinally ignored in research. Neobehaviourists, however, adopted a more liberal posture toward mentalistic states such as consciousness. Neurophysiological mechanisms that consciousness depends on the function of the brain has been known from ancient times. Although detailed understanding of the neural mechanisms of consciousness has not been achieved, correlations between states of consciousness and functions of the brain are possible. Levels of consciousness in terms of levels of alertness or responsiveness are correlated with patterns of electrical activity of the brain waves recorded by an electroencephalograph. During wide-awake consciousness the pattern of brain waves consists of rapid irregular waves of low amplitude or voltage. In contrast, during sleep, when consciousness can be said to be minimal, the brain waves are much slower and of greater amplitude, often coming in periodic bursts of slow waxing and waning amplitude. Both behavioral levels of consciousness and the correlated patterns of electrical activity are related to the function of a part of the brainstem called the reticular formation. Electrical stimulation of the ascending reticular systems arouses a sleeping cat to alert consciousness and simultaneously activates its brain waves to the waking pattern. It was once supposed that the neurophysiological mechanisms subserving consciousness and the higher mental processes must reside in the cortex. It is more likely, however, that the cortex serves the more specialized functions of integrating patterns of sensory experience and orga...
