Circular traveling waves known as sleep spindles occur during non-REM sleep intermediate transition states and last for 1-2 seconds.

“this is uh this is non-rm sleep this is a jargon this is uh during uh intermediate transition States the transition state okay our audience will probably keep they've they've heard a lot about slow wave sleep from me and Matt Walker from Rapid ey light slow a sleep yeah and so what do these traveling waves accomplish for us okay so in the case of the they're called sleep spindles they last the waves last for about u a second or two um and and they travel like I say in a circle around the cortex”