Distribution of the durations of separate segments of records in which lingual EMG exhibited respiratory modulation (RM), and the relationship between the duration of respiratorymodulated segments and respiratory rate. A: most segments of records in which RM of lingual EMG was present, and especially all those longer than 15 s, occurred during slow-wave sleep (SWS). B: with the exception of some very short segments of records, including a few in which RM of lingual EMG occurred during states other than SWS, there was no distinct relationship between RM segment duration and respiratory rate. For segments longer than 15 s, there was no relationship between the duration of the segment and respiratory rate, but data points diverged into two distinct levels due to a generally slower respiratory rate during SWS in Wistar rats than in Sprague-Dawley rats.