Electrical stimulation studies of the human cerebral cortex during surgical exploration and studies by positron emission tomography (PET) have emphasized the importance of the temporal lobe in the genesis of complex visual, auditory, and olfactory hallucinations. Subthalamic and midbrain lesions may give rise to visual hallucinations that are not unpleasant and are accompanied by good insight (“peduncular hallucinosis” of Lhermitte). For reasons not easily explained, with pontine-midbrain lesions, there may be unformed auditory hallucinations.
The EEG in delirium may show symmetrical mild generalized slow activity in the range of 5 to 10 per second. In milder degrees of delirium, there is usually no abnormality at all; this is in stark contrast to the generalized slowing and disruption of EEG activity that accompany most other forms of confusion in proportion to the severity of the clinical state.
Analysis of the conditions conducive to delirium suggests several physiologic mechanisms. Alcohol and sedative drugs are known to have a strong depressant effect on certain regions of the central nervous system; presumably, the disinhibition and overactivity of these parts after withdrawal of the drug are the basis of delirium. Another mechanism is operative in the case of bacterial infections with sepsis and poisoning by certain drugs, such as atropine and scopolamine, in which visual hallucinations are a prominent feature. Here the delirious state probably results from the direct action of the toxin or chemical agent on the same parts of the brain. It has long been suggested that some persons are much more liable to delirium than others, but there is reason to doubt this. Many years ago, Wolff and Curran showed that randomly selected persons developed delirium if the causative mechanisms were strongly operative. This is not surprising, for any normal person may, under certain circumstances, experience phenomena akin to those of delirium. A healthy person can be induced to hallucinate by being isolated for several days in an environment free of sensory stimulation (sensory deprivation). A relationship of delirium to dream states has also been postulated; both are characterized by a loss of appreciation of time, a richness of visual imagery, indifference to inconsistencies, and “defective reality testing.” Formulations in the field of dynamic psychiatry seem more reasonably to explain the topical content of delirium than its occurrence. Wolff and Curran, having observed the same content in repeated attacks of delirium from different causes, concluded that the content depends more on the age, gender, intellectual endowment, occupation, personality traits, and past experiences than on the cause of the delirium.
(See Also Chap. 42)
In considering the pathophysiology of confusion, it must be again emphasized that drug intoxication—including from drugs prescribed by physicians—is among the most common causes in practice. The most distinctive syndromes are those from drugs that have direct or indirect anticholinergic properties. The delirium associated with these agents is centrally mediated but may be accompanied by peripheral anticholinergic manifestations. This point is critical in the differential assessment of agitated confusional states because other compounds, particularly serotonergic agents used to treat depression, also can produce delirium. Thus, in addition to confusion, toxic levels of anticholinergic compounds typically cause dry skin, dry mouth, diminished bowel motility, and urinary hesitancy, if not frank retention. (The clinical maxim that applies is “red as a beet, dry as a bone, blind as a bat, hot as a hare, and mad as a hatter.” The last part of this mnemonic has been also attached to the dementia of mercury intoxication [see Mintzer and Burns].) By contrast, in the toxic serotonergic syndrome associated with excessive doses of the antidepressant drugs, salivation is normal, sweating is increased, and the gut is hyperactive; diarrhea is common. Moreover, the deep tendon reflexes may be exaggerated, and there is often clonus or myoclonus as described by