Relationships in sleep characteristics of identical and fraternal twins.

We recorded EEGs for 14 identical and 14 fraternal young adult twin pairs during one night of sleep in our laboratory. They were instructed to sleep as long as possible. The extended sleep of the identical and fraternal twins was correlated. The structural measures of sleep of the fraternal twins were not correlated. The onset latencies, awakening measures, stage changes, and rapid eye movement amounts were significantly correlated in the identical twins. The nature of the measures used supports an interpretation of hereditary aspects of sleep length and certain structural components of sleep.