Sleep-Wake and Temperature Rhythms in Preterm Babies
Maintained in a Neonatal Care Unit
Clarissa Bueno, Luis Diambra and Luiz Menna-Barreto

Twenty healthy preterm babies with gestational ages between 31^3/7 and 35^3/7 weeks were studied in a low-risk neonatal care unit. Sleep-wake cycle data were collected by the nursery staff through behavioral observation every 10 min as well as the spontaneous or induced nature of awakenings. The data were divided into 10-min epochs, grouped in a series of seven consecutive days, and submitted to spectral analysis. Awakenings were analyzed through a method which calculates the duration of the intervals between the spontaneous or induced awakenings. Oral temperature data, collected every four hours (three consecutive days) were analyzed with the Cosinor technique. An average of 26% of the sleep behavior can be explained by rhythmicity, which is composed by several ultradian frequencies. Three-hour oscillation was the most potent component of the spectrum. Six children expressed a 24-h rhythm. Spontaneous awakenings showed several ultradian rhythms of low potency, whereas induced awakenings expressed a more potent overall rhythmicity. Only one baby expressed a temperature rhythm in the circadian range during the second week of life. These results support the idea that at least part of the sleep-wake rhythmicity identified in babies maintained in a neonatal care unit is generated by external influences.

EEG Power Associated with Early Sleep Onset
Images Differing in Sensory Content
Anne Germain and Tore A. Nielsen

Relationships between known EEG changes occurring at sleep onset (SO) and processes of SO imagery formation are still poorly understood. In the present study, 24 healthy subjects signaled and reported spontaneous SO imagery while in a seated, head-unsupported position. Two judges rated the sensory content of all images. EEG samples immediately preceding the imagery signals as well as from preceding wakefulness were also recorded from a 19-channel montage. EEG samples were categorized by two judges into one of nine SO stages proposed by Hori et al. (1994). Unimodal kinesthetic images (apparent self-movement) and unimodal visual images accompanied only by SO-stage 4 were further subject to spectral analysis, topographically mapped and statistically compared. These SO images were characterized by significant decreases in all frequency bands except delta, for which significant increases were observed over several electrode sites. Kinesthetic and visual images were accompanied by different topographic patterns of delta power: kinesthetic, by prefrontal and frontal delta activation, and visual, by delta activation in more left-central and temporal regions. Results suggest that the documented spread of anterior to posterior delta power occurring for a brief window early in SO may be associated with sense-specific imagery processes unfolding over time. The results are also consistent with a novel explanation for the phenomenon of the "sleep start" which is commonly accompanied by vivid kinesthetic images of falling at the point of sleep onset.

Volitional Lifestyle and Nocturnal Sleep
in the Healthy Elderly
Ai Shirota, Munehisa Tamaki, Hiroshi Nittono, Mitsuo Hayashi and Tadao Hori

The role of lifestyle in nocturnal sleep was examined in the healthy elderly. The Philadelphia Geriatric Center morale scale and the self-confidence scale were used to select high- and low-volitional elderly individuals (n=10 each, mean age=73.2 years). Their activity levels were monitored by a wrist actigraph for 10 consecutive days. On the fourth and eighth nights, polysomnograms were recorded at their homes using an ambulatory monitoring system. Although the daytime activity level did not differ between the groups, high-volitional individuals had better nocturnal sleep than low-volitional individuals: nocturnal awakening was shorter, slow wave sleep was longer, EEG delta power in the first sleep cycle was higher, and the feeling after rising was better. Daily logs revealed that high-volitional individuals spent more time in mental activities during the daytime than low-volitional individuals. These results suggest that a high-volitional lifestyle may contribute to maintaining good nocturnal sleep in the elderly.

Sleep Research Online