Another first for our lab was the discovery of an ultra slow and rhythmic alternation of state in the forebrain of urethane-anaesthetized rats (Clement et al, 2006). Individual states resemble REM and nonREM stages of sleep and the period of their alternations overlaps with the sleep cycle expressed in naturally sleeping animals. Based on these finding and the correspondence of alternations with other physiological measures (EMG, heart rate, and respiration rate) in addition to their dependence upon central cholinergic neuromodulation we have hypothesized that they are a model for the sleep cycle itself. We are currently investigating the similarities and differences observed across anaesthesia using other commonly used agents. We are also testing the effects in our urethane-anaesthetized animals of common sleeping aids which are known to disrupt REM-nonREM cycling in natural sleep. We are also investigating the influence of metabolically important stimuli such as oxygen and temperature on state alternations.