Sleep in the harp seal (Pagophilus groenlandica). Peculiarities of sleep in pups during the first month of their lives.

Two white-coated (ten day-old) and two grey-spotted (one month-old) pups of the harp seal were implanted with electrodes for recording the electrocorticograms of the two hemispheres, electrocardiogram, electrooculogram and electromyogram of the neck muscles. In all individuals ECoG slow waves always developed synchronously in both hemispheres. When white and grey pups were recorded on the snow, the amount of active wakefulness was, respectively, 21.1% (s.e. 11.8%) and 29.9% (s.e. 0.2%) of total recording time, quiet wakefulness = 27.1% (s.e. 4.4%) and 38.2% (s.e. 6.6%), drowsiness = 7.7% (s.e. 0.5%) and 2.07% (s.e. 0.9%), light slow-wave sleep (SWS) = 15.1% (s.e. 3.2%) and 13.0% (s.e. 2.4%), deep SWS = 21.2% (s.e. 2.4%) and 13.8% (s.e. 3.8%), paradoxical sleep (PS) = 8.0% (s.e. 1.4%) and 7.4% (s.e. 1.1%). PS always followed SWS and was fragmented. Respiration was very rare and irregular in PS and a considerable part of PS episodes occurred within a single respiratory pause. During SWS all pups displayed respiratory pauses of up to three minutes, alternating with hyperventilation periods. Heart rate was lowest in PS. Peculiarities of sleep and the pace of sleep pattern development during the first month in seals may be adaptive to the cold environment and ice field drifting in their habitat.