The intellectual, emotional, and behavioral activities of the human organism are so complex and varied that one may question the feasibility of analyzing these activities as reliable indicators of cerebral disease. Certainly they do not have the same tangibility and ease of anatomic and physiologic interpretation as sensory and motor paralysis or aphasia. Yet one observes certain patterns of disturbed higher cerebral function with such regularity as to make them clinically useful in identifying a number of diseases. Some of these disturbances gain specificity because they are combined in ways that form clinical syndromes.
The components of mentation and behavior that lend themselves to observation and examination are (1) attention; (2) perception and apperception (awareness and interpretation of sensory stimuli); (3) the capacity to form new memories and to recall events of the recent and distant past; (4) the ability to think and reason; (5) temperament, mood, and affect; (6) initiative, impulse, and drive; (7) social behavior; and (8) insight. Of these, the first two are sensory, the third and fourth are cognitive, the fifth is affective, the sixth is conative or volitional, the seventh refers to the patient’s relationships with those around him, and the last refers to the patient’s capacity to assess his own functioning. Each component of behavior and intellect has its objective side, expressed in the behavioral responses produced by certain stimuli, and its subjective side, expressed in the thinking and feeling described by the patient. Less accessible to the examiner, but nevertheless possible to study by questioning the patient, are the memory, planning, and other activities that continuously occupy the mind of an alert person. They, too, are disordered or quantitatively diminished by cerebral disease.
Disturbances of Attention
Critical to clear thinking is a process of maintaining awareness of one or a limited number of external stimuli or internal thoughts for a fixed period of time and to simultaneously disregard the numerous distracting sensations and ideas that constantly bombard the nervous system. Without this ability to focus or “pay attention” and have an “attention span,” a coherent stream of thought or action is not possible. The undue interruption of these activities by the intrusion of other thoughts or actions is termed inattention, or distractibility. Two essential components are embodied in the attention mechanism: one, a continuous state of alertness that is normally present throughout waking life (and underlies self-awareness); the other, a process of selecting from the myriad sensations and thoughts those that are relevant to the immediate situation to the exclusion of others.
The confused patient may demonstrate inattention in almost every task undertaken. If the degree of confusion is slight, the patient may report a difficulty with concentration. If severe, there is a parallel lack of insight and the problem is evident by easy distractibility by ambient stimuli and by impersistence and perseveration in conversation and motor tasks. Restated, attention has such a pervasive effect on all other aspects of mental performance that it is often difficult to determine whether the confused patient also has primary disorders of memory, executive, or visuospatial function. Indeed, retentive memory may be severely reduced in confusional states. Furthermore, the ability to carry out a series of actions or mental operations wherein one is required to hold in memory the result of the previous operation (“working memory”) is intimately tied to attention and is particularly prone to disruption in confusional states.
The general ability to persist in a motor or mental task emphasizes an executive side of attention, but here one encounters a problem because the term attention has been applied to a number of seemingly different mental activities. One can view attention as a separate and unique cerebral function or simply a way of referring to the persistence or impersistence of any activity. We would argue that the entire cerebrum participates in attentiveness and the frontal and perhaps the parietal lobes are responsible for directing its content, but that the thalamocortical system is in a special way responsible for its raw maintenance. Mesulam, who has written substantially about this problem, considers the frontal and parietal lobes to be at the nexus of an “attentional matrix”; in his model, the prefrontal, parietal association, and limbic cortices direct and modulate attention in an executive manner. Certainly, the temporal lobes and other regions are involved as well.