The REM cycle, combining rules, and age.

Standardized scoring of the EEG records of older subjects (50 years or older) revealed frequent brief interruptions of the REM periods. In the absence of rules that would permit incorporation of these transient interruptions, there is a marked increase in the number of REM episodes and a significant change in average period length and REM cycle measures. This paper explores the use of rules that combined the interruptions of different lengths (5 min and 15 min) in the ongoing REM period. Populations of 40 males and 40 females who were 50-60 years old were compared with samples of 15 males and 15 females between 19 and 31 years of age. The use of combining rules had little effect on the younger samples and a limited effect on the older females. For the males the use of combining rules reduced the number of periods by one-half and doubled the average REM period length and the REM cycle. While these measures approximate the normative figures of the other samples, they remain significantly different from them. Scoring of all records by a 5-min combining rule is recommended, as is also the use of no-rule scoring as a measure of REM period stability.