Much more could be said about the history of our ideas concerning consciousness, and the theoretical problems with regard to its definition. There has been an ongoing polemic among philosophers of mind as to whether it will ever be possible to understand mind and consciousness in terms of reductionist physical entities, such as cellular and molecular neural systems. Although it serves little practical purpose to review these subjects here, we note that contemporary investigations indicate that one constructive approach is to define the neurobiologic correlates of those elements of clinical consciousness that are subject to observation by behavioral, electrical, and particularly imaging methods. Importantly, these controversies are informed in neurology by analyses of those neurologic disorders that disturb perception and consciousness of perception (phantom limb, “blindsight,” etc.). The interested reader is referred to the discussions of consciousness by Crick and Koch, Plum and Posner, Young, and Zeman listed in the references.
The following definitions are of service to clinicians and provide a convenient terminology for describing the states of awareness and responsiveness of patients.
This is the condition of the normal person when awake. In this state the individual is fully responsive to a thought or perception and indicates by his behavior and speech the same awareness of self and environment as that of the examiner. There is attention to, and interaction with, the immediate surroundings. This normal state may fluctuate during the day from one of keen alertness or deep concentration with a marked constriction of the field of attention to one of mild general inattentiveness, but even in the latter circumstances, the normal individual can be brought immediately to a state of full alertness and function.
The term confusion admittedly lacks precision, but in operational terms it denotes an inability to think with customary speed, clarity, and coherence. Almost all states of confusion are marked by some degree of inattentiveness and disorientation and for some investigators, these two qualities define the state. In this condition the patient does not take into account all elements of his immediate environment. This state also implies a degree of imperceptiveness and distractibility, referred to in the past as “clouding of the sensorium.” Here, one difficulty is to define thinking, a term that refers variably to problem solving or to coherence of ideas. Confusion results most often from a process that influences the brain globally, such as a toxic or metabolic disturbance or a dementia. In addition, any condition that causes drowsiness or stupor, including the natural state that comes from sleep deprivation, results in some degradation of mental performance and the emergence of inattentiveness and a state of confusion. In this way, confusion, which exists along the axis of content of consciousness, is linked to alertness and the level of consciousness.
A confusional state can also accompany focal cerebral disease, particularly in the right hemisphere, or result from focal disorders that disturb mainly language, memory, or visuospatial orientation, but a distinction is made between these isolated disruptions in mental function and the global confusional state. They represent special states that are analyzed differently, matters discussed further in Chaps. 19 and 21.
The mildest degree of confusion may be so slight that it can be overlooked unless the examiner searches for deviations from the patient’s normal behavior and ability to carry on a coherent conversation. The patient may even be roughly oriented as to time and place, with only occasional irrelevant remarks betraying a lack of clarity and slowness of thinking. Their responses are inconsistent, attention span is reduced, and they are unable to stay on one topic, together suggesting a fundamental flaw in attention.
As mentioned this is usually accompanied by disorientation and distractibility, leaving the patient at the mercy of every stimulus. In parallel, sequences of movement reveal impersistence and poor planning.