Paradoxical sleep and coping with environmental change.

Long-term sleep recordings of mice from 3 inbred strains showed that the amount of time spent in sleep over successive 24-h periods varied as the subjects adapted to experimental conditions. A sinusoidal type variation, with a period of about 15 days, modulating the basic trends in sleep times is described; but the principal finding of this study relates to a monotonic decrease in Paradoxical Sleep (PS) as recording continued. Age, stimulus deprivation and fatigue effects do not appear to be causative factors for this decrement, indicating that the changes in PS might reflect a habituation process. On this basis it is hypothesized that an increase in PS time in the mouse is a specific response to a significant environmental stimulus and could, therefore, form part of the coping strategy. This hypothesis is generalized and discussed in terms of its implications, both for experimentation concerned with measuring PS times and with the possible functional significance of PS.