PT  - JOURNAL ARTICLE
AU  - Siegel, J. M.
AU  - Manger, P. R.
AU  - Nienhuis, R.
AU  - Fahringer, H. M.
AU  - Pettigrew, J. D.
TI  - 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
AID  - 10.1523/JNEUROSCI.16-10-03500.1996
DP  - 1996 May 15
TA  - The Journal of Neuroscience
PG  - 3500--3506
VI  - 16
IP  - 10
4099  - http://www.jneurosci.org/content/16/10/3500.short
4100  - http://www.jneurosci.org/content/16/10/3500.full
SO  - J. Neurosci.1996 May 15; 16
AB  - 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.