Physiological and psychological factors in sleep-onset insomnia.

A group of insomniacs whose only sleep-stage abnormality was prolonged sleep latency was identified. Prior to sleep onset, these subjects had significantly higher levels of physiological activity than did normal sleepers. With the approach of sleep onset, these differences diminished. No group differences in presleep cognitive activity were found. Insomniacs had significantly higher Minnesota Multiphasic Personality Inventory (MMPI) scores than normal on scales indicating neuroticism, anxiety, and worry (derived from the Hysteria, Psychasthenia, and Schizophrenia scales). Although sleep-onset insomnia is accompanied by psychological disturbance and heightened physiological activity, it is unlikely that either factor alone is sufficient to cause it. Excessive rumination may be an epiphenomenon of sleeplessness. Chronic insomnia is a distressing complaint that affects millions of persons (Solomon, 1979). Three general types of insomnia have been described: initial, or sleep-onset; intermittent, or sleep-maintenance; and terminal, or early morning awakening (Kleitman, 1963). The present investigation is concerned with primary idiopathic sleep-onset insomnia: the inability to fall asleep in the absence of identifiable physiological or psychological determinants. Many theories have been advanced to explain idiopathic insomnia (Rechtschaffen & Monroe, 1969). Two of the most popular suggest that insomniacs are either physiologically or cognitively hyperaroused relative to normal (Association of Sleep Disorders Centers, 1979; Borkovec, 1979). Support for the first hypothesis has rested largely on a study by Monroe (1967), demonstrating that self-defined poor sleepers had higher levels of physiological activity than good