Independence of sleep-wakefulness cycle in an implanted head 'encephale isole'

A quantitative study was carried out on the sleep-wakefulness cycle by means of EEG recordings taken simultaneously from a dog's implanted head and its host. During survival (108 h), neurological activities of the implanted head were similar to those of classic 'encéphale isolé' preparations. In spite of a common circulation, the sleep-wakefulness cycles of the implanted head and host animal were independent. Independence was manifested by: (1) differing percentages of respective phases of their cycles; (2) periods of coincident phases in both heads, only occasionally beginning and/or stopping simultaneously; and (3) the implanted 'encéphale isolé' showed a monotonous cycle with numerous periods of short duration throughout night or day. The host presented a nycthemeral rhythm.