segmented sleep

a pattern in which two periods of nighttime sleep are separated by an extended period of wakefulness. It has been suggested that this pattern, called first sleep and second sleep and often involving a third period of light sleep during the day, may have been the norm for human beings before industrialization and the advent of electric lighting. See polyphasic sleep. [described by U.S. historian A. Roger Ekirch in 2001]

Browse dictionary by letter

a b c d e f g h i j k l m n o p q r s t u v w x y z

Psychology term of the day

February 17th 2025

sexually dimorphic nucleus

a nucleus of the central nervous system that differs in size between males and females. In humans, for example, a nucleus in the medial preoptic area of the hypothalamus that synthesizes gonadotropin-releasing hormone tends to be larger and more active in males than in females because gonadotropin release is continuous (it is cyclical in females). In songbirds whose males sing more than females, several brain nuclei associated with both song learning and song production are larger in males than in females.