Many elderly people complain of significant sleep disturbance. Complaints of multiple and prolonged awakenings and fragmented nocturnal sleep indicate that elderly individuals have difficulties in maintaining, rather than initiating sleep. Age-related changes in the circadian system underlie, at least in part, sleep disturbance. Timed exposure to bright light can alleviate such symptoms, although compliance to long-term treatments is poor. As such, alternatives and/or supplements to bright light are needed to relieve sleep disturbance. In humans, light phase shifts circadian rhythms according to a phase response curve. Nonphotic stimuli, such as social interaction, and sensory stimuli including auditory and olfactory cues, can also phase shift circadian rhythms in mammals and birds. Few studies have investigated rigorously whether nonphotic stimuli can affect human circadian rhythms. This study will determine whether an auditory stimulus, with an arousing component, can phase shift circadian rhythms in a sample of healthy male and female elderly (60+ yr old) subjects. An ancillary question will assess gender differences in response to auditory stimuli in the elderly. Subjects will spend two 4-day sessions in a sleep laboratory under constant dim light (less than 20 lux), receiving either a 2-h auditory stimulus or a control stimulus (absence of auditory cue) from 0100 h-0300 h on the second and third nights. Subjects will participate in both sessions, with presentation order counterbalanced among individuals. Polysomnographical sleep and core body temperature will be collected continuously and salivary melatonin samples will be obtained once each hour from 1800 h to 2400 h on Night 1 (baseline night) and Night 4 (post-stimulus night). To measure putative phase shifts, circadian phase of core body temperature minimum and the dim light melatonin onset (DLMO), before and after sensory stimulation, will be assessed in the control and experimental sessions. This study serves as the first essential step toward describing rigorously the effects of sensory stimuli on circadian rhythms in males and females. Completion of this project will allow for further exploration regarding the significance of nonphotic entrainers for the human circadian system, in particular as alternatives for relieving sleep disturbance in older subjects.
| Goel, Namni (2006) An arousing, musically enhanced bird song stimulus mediates circadian rhythm phase advances in dim light. Am J Physiol Regul Integr Comp Physiol 291:R822-7 |
| Goel, Namni (2005) Late-night presentation of an auditory stimulus phase delays human circadian rhythms. Am J Physiol Regul Integr Comp Physiol 289:R209-16 |
