Patricia J. Murphy

Effects of a Nap on Nighttime Sleep and Waking Function in Older Subjects

Objectives: To examine, in older subjects, the effect on waking function of increasing 24‐hour sleep amounts by providing a nap opportunity; to assess what effects an afternoon nap may have on subsequent nighttime sleep quality and composition.

Physiology of the circadian system in animals and humans.

Virtually all organisms have developed an internal timing system capable of reacting to and anticipating environmental stimuli with a program of appropriately timed metabolic, physiologic, and behavioral events. The predominant biological rhythms coincide with the geophysical cycle of day and night-the circadian rhythms. The suprachiasmatic nuclei comprise the primary pace-maker in mammals, exhibiting the properties fundamental to a rhythm-generating structure. This article summarizes recent research that has elucidated mechanisms of signal transduction within the circadian system. The roles of various neurochemicals and hormones in transmitting the circadian timing signal are described. Properties of the circadian system, including photic and nonphotic entrainment, phase response curves, masking, and the intrinsic variability in the system are discussed.

Enhanced performance in elderly subjects following bright light treatment of sleep maintenance insomnia

Sixteen older individuals with sleep maintenance insomnia were treated with night‐time bright‐light exposure (BL) while living at home. Twelve consecutive days of acute light treatment were followed by a 3‐mo maintenance light‐treatment period. Subjects completed laboratory evaluation sessions on five separate occasions (prior to and following the acute light‐treatment period, and once per month during the maintenance period). During each laboratory session, performance levels, sleep, and core body temperature were measured. The performance battery consisted of four computerized tasks (Logical Reasoning, Stroop Congruency, Two Letter Visual Search, and Wilkinson Four‐Choice Reaction Time) and was administered every 2 h between 10.00 and 18.00 hours. Subjects improved significantly on three of the four tasks from pre‐BL to post‐BL. During the maintenance period, subjects who received active BL treatment maintained significantly higher performance levels than a control BL group. Light treatment improved sleep efficiency and delayed the phase of the body temperature rhythm. Performance improvements were significantly related only to sleep and not to circadian phase. The implications for non‐circadian treatments of sleep maintenance insomnia and cognitive functioning in the elderly are discussed.

Etiology and treatment of intrinsic circadian rhythm sleep disorders

Some individuals experience an acute or chronic sleep disturbance, associated with a misalignment between the timing of their sleep and the sleep-wake cycle that is desired, or considered normal by society. It is estimated that 5-10% of insomniacs seeking treatment have this type of disorder, collectively called circadian rhythm sleep disorders. This paper reviews circadian rhythm sleep disorders of the intrinsic type, which include delayed sleep phase syndrome, advanced sleep phase syndrome, non-24-hour sleep-wake syndrome, and irregular sleep-wake pattern. For each disorder, we present data addressing its pathophysiology and potential treatments, including the use of behavioral measures and chronotherapy, bright light treatment and pharmacological treatments such as melatonin. We conclude by addressing some of the limitations and drawbacks of the various treatments.

Relationships Between Sleep and Body Temperature in Middle-Aged and Older Subjects

OBJECTIVES: Although changes in the circadian timing system are thought to be a major factor in the decline of sleep quality that often accompanies aging, few reports have actually examined this relationship in detail. Because some treatments for age‐related insomnia are based on putative circadian changes, it is important to expand the limited database that specifically addresses this issue. This study examined age‐related changes in sleep, and relationships between those sleep changes and alterations in the circadian timing system, in a group of middle‐aged and older subjects.

Failure of Timed Bright Light Exposure to Alleviate Age‐Related Sleep Maintenance Insomnia

To determine whether a twice‐weekly maintenance schedule of evening bright light exposure is effective in alleviating sleep maintenance insomnia on a long‐term basis, after the establishment of a more favorable phase relationship between the core body temperature (CBT) rhythm and sleep.

The nature of spontaneous sleep across adulthood

The decline in sleep quality that often accompanies aging is thought to be the consequence of alterations in both circadian and homeostatic processes widely assumed to be responsible for sleep/wake regulation. A number of experimental approaches have been used to examine various aspects of age‐related sleep changes, but none has examined spontaneous sleep across the entire 24‐h day. Using the ‘disentrainment’ protocol, we studied such sleep in young, middle‐aged and older adults. All subjects exhibited polyphasic sleep patterns, characterized by relatively short intervals of both sleep and waking. Whereas, the average duration of major nighttime sleep was significantly shorter in middle‐aged and older subjects than in young adults, daytime napping was essentially unaffected by age. Comparisons of sleep and circadian variables between age groups suggest differential effects on sleep of the two regulatory processes, with changes in homeostatic drive preceding those of the circadian component. These findings add to a surprisingly scant literature on the longitudinal decline in sleep quality associated with aging.

EXTRAOCULAR PHOTOTRANSDUCTION AND CIRCADIAN TIMING SYSTEMS IN VERTEBRATES

It is widely accepted that, for organisms with eyes, the daily regulation of circadian rhythms is made possible by light transduction through those organs. Yet, it has been demonstrated repeatedly in recent years that ocular light receptors that mediate vision, at least in mammals, are not the same photoreceptors involved in circadian regulation. Moreover, it has been recognized for many years that circadian regulation can occur in organisms without eyes. In fact, extraocular circadian phototransduction (EOCP) appears to be a phylogenetic rule for the vast majority of species. EOCP has been reported in every nonmammalian species studied to date. In mammals, however, the story is very different. This paper presents findings from studies that have examined specifically the capacity for EOCP in vertebrate species. In addition, the literature addressing noncircadian aspects of extraocular phototransduction is briefly discussed. Finally, possible mechanisms underlying EOCP are discussed, as are some of the implications of the presence, or absence, of EOCP across phylogeny. (Chronobiology International, 18(2), 137–172, 2001)

Long-term time estimation is influenced by circadian phase

The adaptive significance of a putative time sense in humans remains unclear as do the factors that underlie the capacity to gauge the passage of time. Here we show that the subjective assessment of relatively long durations varies systematically as a function of time of day. Specifically, the subjective clock ran relatively faster when the circadian oscillation of body temperature was on the rise and relatively slower on the declining portion of the temperature curve. The overall result was a rather labile clock that, on average, ran slow relative to physical time. The results provide a glimpse into an underexplored aspect of how humans use their endogenous clocks in the most fundamental way--to gauge the passage of time.

Effects of a Month-Long Napping Regimen in Older Individuals

OBJECTIVES: To examine the effects of a month‐long nap regimen using one of two durations (45 minutes or 2 hours) on nighttime sleep and waking function in a group of healthy older participants and to assess the degree to which healthy older individuals are willing and able to adhere to such napping regimens.