ORGANIZATION OF SLEEP-WAKING STATES IN CONJOINED TWIN NEONATES

Developmentally normal twins, joined from the mid-sternum to the umbil icus in a face-to-face position, were observed in 90-minute sessions t wice daily from postnatal days 12 to 16. Sleep-waking states were code d in 10-second epochs. Within-twin data were analyzed for bout lengths , interbout intervals, transition probabilities and 60-minute autocorr elation patterns. Between-twin data were studied for simultaneous occu rrences of sleep-waking states and 60-minute cross-correlation pattern s. Epochs per bout and interbout intervals for quiet and active sleep, active sleep epochs with rapid eye movements (REMs) and quiet and act ive waking states showed little difference between the twins over the study days. Probabilities of transition between quiet and active sleep and active wakefulness also showed the same patterns for each twin. H owever, the organization of temporal states differed markedly. Simulta neous occurrences of the same states were at or barely above chance le vels, autocorrelation patterns of all states except epochs with REMs w ere not the same and cross-correlations indicated little influence of one twin's current state on the subsequent probability of that state's occurrence in the other twin. Thus, neither shared environment, ident ical genotype nor shared stimulation from co-twin motor activity appea red to synchronize the temporal organization of behavioral states in t hese twins. We concluded that the overall distributions of neonatal sl eep-waking states seem to be determined primarily by age, whereas the temporal organization of states expresses the neonate's individuality.