Fig. 2. Rat polysomnography. Experiment in a chronically instrumented rat (sleep experiment). Typical transition from non–rapid eye movement (REM) to REM sleep.  First arrow = point of conversion of theta/delta ratio to greater than 1.  Second arrow = start point of genioglossus activity measurements (low neck-muscle activity).  Third arrow = endpoint of genioglossus activity measurements (onset of tongue muscle twitches). EEG = electroencephalogram; EMG = electromyogram; GG = genioglossus; MTA = moving time average.