(A) Top: For all ECN recordings, P8-10 rats were instrumented with forelimb (blue) and nuchal (red) EMGs (n = 22). A subset of these rats also had a hindlimb (green) EMG (n = 9). The torso was supported by a platform and the limbs dangled freely. Bottom left: Coronal brain section depicting the anatomical location of the ECN in the hindbrain (inset; red dashed line depicts AP position of the coronal section). Bottom right: Sample record of a burst of ECN reafference in response to forelimb twitches. (B) Left: Event correlations for unit activity in relation to forelimb (blue, n = 8146 twitches), nuchal (red, n = 9603 twitches), and hindlimb (green, n = 1243 twitches) twitches. The colored dashed lines denote upper acceptance bands (p<0.01) for the event correlations. Right: Pairwise comparisons of mean (+SEM) peaks in unit activity (Hz) in response to forelimb, nuchal, and hindlimb twitches. Comparisons are between forelimb and nuchal muscles (top), forelimb and hindlimb muscles (middle), and nuchal and hindlimb muscles (bottom). (C) Left: Representative data depicting sleep and wake behavior, MUA, and forelimb and nuchal EMG during spontaneous sleep-wake cycling. Red tick marks denote forelimb twitches, and red horizontal bars denote forelimb wake movements as scored by the experimenter. Right: Mean (+SEM) unit activity (n = 16) during wake and active sleep (AS) periods. * significant difference from active sleep, p<0.05. (D) Left: Event correlations for evoked unit activity in response to forelimb stimulations performed during active sleep (n = 188 stimulations) and wake (n = 238 stimulations) across 6 ECN units in six pups. Right: Mean (+SEM) peak unit activity (n = 6) derived from event correlations during wake and active sleep. ECN, External cuneate nucleus; MUA, Multiunit activity.