Polygraphic sleep study in craniopagus twins (where is the sleep transmitter?)

By means of polygraphic recordings complete independence of the sequence of sleeping and waking and of the two sleep states (REM and NREM) could be demonstrated in twins extensively conjoined at the skulls. Functionally important connections in the circulation of the two babies were found during subsequent preoperative investigations. These observations are at variance with the hypothesis of an extraneuronal humoral sleep-inducing factor based on crossed-circulation experiments in animals; moreover they raise a new question about the transportation of the sleepregulating biogenic amines.