<p>In normal adults, a cycle of sleep stages repeats throughout the night, about every 90 minutes. This is referred to as “sleep architecture.”<br></p><p style="text-align: center;"><img src="@@PLUGINFILE@@/sleep-architecture-evening.png" alt="Figure : Sleep Architecture over the Course of an Evening of Sleep" width="660" height="383" class="img-responsive atto_image_button_text-bottom"><br></p><p style="text-align: center;">Figure : Sleep Architecture over the Course of an Evening of Sleep<br></p><p style="text-align: center;"><br></p><p><b>NREM1 </b>= Alpha begins to slow and intermittently drop out of the record and we see a suppression of EEG amplitude, overall.&nbsp;</p><p><b>NREM2 </b>= The presence of Vertex Sharp Waves, K-Complexes, and Sleep Spindles</p><p><b>NREM3</b> = The movement towards complete slow waves (Delta and some low frequency theta)</p><p><b>NREM4</b>&nbsp; = Deep dreamless sleep, aka “Slow Wave Sleep (SWS)</p><p><b>REM </b>= Rapid Eye Movement Sleep</p><p>Some schools of thought now combine Stage 3 and Stage 4 of sleep.</p>