Fig. 8. Chronically instrumented rats: Relation between electroencephalogram power spectrum and genioglossus electromyogram in chronically instrumented rats. Five repetitive measurements from eight rats. Red symbols:  wakefulness; blue symbols:  nonrapid eye movement sleep; green symbols:  rapid eye movement sleep; turquoise symbols:  low-dose ketamine anesthesia (60 mg/kg); black symbols:  high-dose ketamine anesthesia (125 mg/kg). (A  and B ) Not anesthetized: genioglossus electromyogram positively correlates with δ activity (A ). There is a trend toward negative correlation with θ activity (B ). (C  and D ) During ketamine anesthesia: the relation between electroencephalogram and electromyogram is abolished, i.e ., sleep and genioglossus dysfunction are uncoupled. AU = arbitrary units; EEG = electroencephalogram; EMG = electromyogram; REM = rapid eye movement sleep.