Recent human infant studies have underscored the importance of temperature as a possible trigger for Sudden Infant Death Syndrome (SIDS). However, the specific mechanisms by which temperature may lead to SIDS are unknown. Our hypothesis is that temperature plays an integral role control of breathing. The use of the rat pup as an animal model offers an opportunity to examine the interaction of temperature with sleep and breathing in the early postnatal period. The amount and pattern (sleep architecture) of sleep and arousal depend significantly on ambient temperature. Our analysis of sleep architecture at neutral and warm environmental temperatures will focus on the influence of ambient temperature on the temporal organization of sleep and wakefulness at several stages of early postnatal development. Core temperature has also been shown to have a strong influence on the timing and distribution of arousal states in adults. Significant modifications in the total amount and distribution of specific sleep states in infants could result from hyperthermia induced either exogenous (high room temperature or overbundling) or endogenous (fevers induced by DTP immunization) sources. Additionally, small elevations of skin temperature can dramatically modulate respiratory pattern, but it is unknown if this effect is due primarily to a direct influence of respiration by temperature or, instead, to changes in sleep architecture. Moreover, hyperthermia has been shown to decrease upper airway patency. In adults, body temperature is regulated at a lower level in quiet sleep compared to wakefulness, and thermal and respiratory control is severely inhibited in active sleep. However, little information exists on thermoregulatory and respiratory reflexes are inhibited during this sleep state, and to measure the interaction of thermal and respiratory stimuli on arousal thresholds during sleep. Because of the recent correlation between prone sleeping position, heat loss, and SIDS risk, we will investigate how changes in temperature of infants sleeping prone vs supine modify sleep architecture and arousal. Both preterm and term infant groups will be studied longitudinally to quantify hypercarbia challenges during different sleep states. The overall goal of this project is to determine how systems controlling sleep structure, arousal, and thermal homeostasis interact and are modulated by temperature in the infant.