• Subjects with a primary complaint of insomnia (N = 124) were evaluated with Minnesota Multiphasic Personality Inventories (MMPIs). A high percentage of subjects (85%) had one or more MMPI scales elevated to a pathological degree. The scales most elevated were, in order, 2 (depression), 7 (psychasthenia), and 3 (conversion hysteria). A striking finding was the preponderance of depression. This was indicated by the frequency in which scale 2 was elevated above 70, the frequency in which this scale had the highest elevation, and the frequency of MMPI code types that included scale 2. Four common MMPI code types representing various types of depression were noted, indicating considerable homogeneity for code types in this sample.

The predominant personality styles in this sample were characterized by the internalization of psychological disturbances rather than by acting out or aggression. We propose that this internalization produces a state of constant emotional arousal and resultant physiological activation and that this process is a psychophysiological mechanism underlying insomnia.