Sleep deprivation in pigeons and rats using motion detection.

SIGNIFICANT ATTENTION HAS BEEN GIVEN TO THE EFFECTS OF SLEEP LOSS ON PHYSIOLOGY,1 GENE EXPRESSION,2 IMMUNE FUNCTION,3–5 THE STRESS RESPONSE,6,7 and various behavior measures of motivation,8,9 learning,10,11 and performance.12 The most thoroughly examined animal model for studies of sleep deprivation or restriction is the rat. When subjected to long-term sleep deprivation, rats exhibit a well-defined physiologic sleep deprivation syndrome (SDS), the most prominent features of which are increased food intake with progressive weight loss, thermoregulatory changes, debilitated appearance, and lesions on the tail and plantar surfaces. Death can result if sleep deprivation is continued for several weeks.1,13–15 These experiments using the disk-over-water (DOW) method have provided valuable insights into the effects of sleep deprivation, but whether the observed effects are specific to rats is uncertain. Similar consequences of sleep deprivation might be seen in other mammals or even other taxa, but species other than the rat have not been extensively studied. We have tried to replicate the rat SDS in pigeons using the DOW,16 and the results of this work illustrate how difficulties in implementation complicate the interpretation of sleep-deprivation results. These pigeons showed none of the features of the rat SDS. They appeared normal and healthy even after up to 29 days of sleep deprivation, although, like rats, they showed compensatory rebound sleep, composed primarily of rapid eye movement (REM) sleep. Nonetheless, it was not possible to conclude from these data that pigeons were more resistant to the effects of long-term sleep deprivation than were rats because the DOW was not as effective at inducing sleep loss in the birds as in the rats. Total sleep time was reduced by only 54%, much less than the 91% reduction originally reported in the rat literature17 or even the 82% reduction seen when rat sleep-wake state is scored using 4-second epochs.2 The birds may indeed have been more resistant than rats to the effects of sleep loss, or they may not have been sufficiently deprived of sleep to produce the symptoms of the SDS. To see whether the effect of sleep loss in pigeons is similar to the effect of sleep loss in rats, it is necessary to reduce sleep by a similar proportion in the 2 species, preferably using the same apparatus. To this end, we modified the DOW to achieve a more thorough sleep deprivation in the pigeon. We observed 2 major problems with using the DOW in pigeons: (1) the pigeons were much more adept than the rats at “riding” the disk and sleeping against a wall as the disk rotated beneath them and (2) the match between the physiologic state and the onset of disk rotation was worse in the pigeons than in the rats, largely because the electromyography (EMG) and electroencephalography (EEG) signals alone do not reliably differentiate sleep from quiet wakefulness in most birds, including pigeons.18–20 We addressed the first problem of disk riding by changing the DOW to a conveyor-over-water (COW) in which the floor always moved the animal toward the water, thus making it impossible to ride the belt. We addressed the second problem of physiologic state response by replacing the EEG or EMG triggering of the arousing stimulus with triggering by detection of inactivity. Behavioral quiescence proved to be an accurate indicator of sleep onset in the pigeons during the DOW experiments, perhaps more reliable than EEG signals. Furthermore, relying on quiescence detection alone eliminates the issue of distinguishing between mixed states in the EEG to induce belt rotation. With this remodeled apparatus, we subjected both rats and pigeons to total sleep deprivation by the same method, using short (4-second) epochs and recording EEG and EMG for verification of vigilance state. The primary goals of the study were to determine whether similar physical stimuli could produce equivalent sleep loss in a bird and a mammal and to see whether sleep loss resulted in the same systemic and electrophysiologic effects.