TY - JOUR T1 - The Echidna <strong><em>Tachyglossus aculeatus</em></strong> Combines REM and Non-REM Aspects in a Single Sleep State: Implications for the Evolution of Sleep JF - The Journal of Neuroscience JO - J. Neurosci. SP - 3500 LP - 3506 DO - 10.1523/JNEUROSCI.16-10-03500.1996 VL - 16 IS - 10 AU - J. M. Siegel AU - P. R. Manger AU - R. Nienhuis AU - H. M. Fahringer AU - J. D. Pettigrew Y1 - 1996/05/15 UR - http://www.jneurosci.org/content/16/10/3500.abstract N2 - Placental and marsupial mammals exist in three states of consciousness: waking, non-REM sleep, and REM sleep. We now report that the echidna Tachyglossus aculeatus, a representative of the earliest branch of mammalian evolution (the monotremes), does not have the pattern of neuronal activity of either of the sleep states seen in nonmonotreme mammals. Echidna sleep was characterized by increased brainstem unit discharge variability, as in REM sleep. However, the discharge rate decreased and the EEG was synchronized, as in nonREM sleep. Our results suggest that REM and non-REM sleep evolved as a differentiation of a single, phylogenetically older sleep state. We hypothesize that the physiological changes that occur during postnatal sleep development parallel certain aspects of the changes that have occurred during the evolution of sleep–waking states in mammals. ER -