The medical literature is replete with references to illnesses based on emotional disorders. Careful examination of clinical material discloses that diverse phenomena are being so classified: anxiety states, cycles of depression and mania, reactions to distressing life situations, psychosomatic diseases, and illnesses of obscure nature. Obviously, great license is being taken with the term emotional. Such ambiguity renders neurologic analysis difficult. Nevertheless, in certain clinical states patients appear to be excessively apathetic or elated under conditions that are not normally conducive to such displays of emotion. It is to these disturbances that the following remarks pertain. Emotion may be defined as any feeling state—for example, fear, anger, excitement, love, or hate—associated with certain types of bodily changes (mainly visceral and under control of the autonomic nervous system) and leading usually to an impulse to action or to a certain type of behavior. If the emotion is intense, there may ensue a disturbance of intellectual functions, that is, a disorganization of rational thought and a tendency toward a more automatic behavior of unmodulated, stereotyped character.
In its most easily recognized human form, emotion is initiated by a stimulus, real or imagined, the perception of which involves recognition, memory, and specific associations. The emotional state that is engendered is mirrored in a psychic experience, i.e., a feeling, which is purely subjective and known to others only through the patient's verbal expressions or by judging his behavioral reactions. This behavioral aspect, which is in part autonomous (hormonal–visceral) and in part somatic, shows itself in the patient's facial expression, bodily attitude, vocalizations, or directed voluntary activity, an observable display for which we use the term affect. In other words, the components of emotion appear to consist of (1) the perception of a stimulus, which may be internal (an idea) or external, (2) the feeling, (3) the autonomic–visceral changes, (4) the outward display (affect), and (5) the impulse to a certain type of activity. In many cases of neurologic disease, it is not possible to separate these components from one another, and to emphasize one of them does no more than indicate the particular bias of the examiner. Obviously, neural networks of both affective response and cognition are involved.
The occurrence of abnormal emotional reactions in the course of disease is associated with lesions that preferentially involve certain parts of the nervous system. These structures are grouped under the term limbic and are among the most complex and least understood parts of the nervous system. The Latin word limbus means "border" or "margin." Credit for introducing the term limbic to neurology is usually given to Broca, who used it to describe the ring of gray matter formed primarily by the cingulate and parahippocampal gyri that encircles the corpus callosum and underlying upper brainstem. Actually, Thomas Willis had pictured this region of the brain and referred to it as the limbus in 1664. Broca preferred his term, ...