A circadian perspective of first night effect and its relationship to vigilance and short-term memory.

Abstract

Hospitalization, a significant environmental alteration, is hypothesized to produce first night effect (FNE), a transient phase shift in the timing of sleep-wake in a 24-hour context. The extent to which this effects circadian rhythms and subsequent cognitive performance is unknown. This quasi-experimental, interrupted time series study examined the circadian nature of FNE, vigilance, and short-term memory (STM). Sleep-wake activity and core body temperature were monitored for 96 hours in home and hospital settings in eleven healthy females (22-41 years). Vigilance and STM performance were assessed at six intervals. Two-tailed paired samples tests revealed that, in the hospital, subjects went to bed later, woke up earlier, and experienced a shorter nocturnal sleep period with less nocturnal sleep (p $\le$.05). Times of low nocturnal temperatures occurred significantly later in the sleep period (by 54 minutes) and peak diurnal temperatures occurred later (by approximately 7 hours) in the waking period (p $\le$.05). Vigilance and memory scores revealed greater vigilance at home $(t=2.424,$ p =.036), and improved memory performance in the hospital $(t={-}2.796,$ p =.019). In healthy women, environmental alteration did not evoke heightened vigilance; it provoked a significant transient phase shift in core body temperature curves and timing of sleep-wake extending beyond 24 hours. It is concluded that FNE is a circadian phenomenon and suggested that these effects may be intensified among vulnerable patient populations.