Figure 2. Changes in muscle tone and heart rate during experimental arousal for trials without RMMA. (A) An increase in EMG activity in suprahyoid (SH) and masseter (MAS) muscles for sleep stage 2 (St2) and rapid eye movement sleep (REM). No group difference was found (p > 0.05 for all, ANOVA). EMG was averaged for periods of -2 to 0 sec (-1), 0 to 2 (1), 2 to 4 (3), and 4 to 6 (5) after stimulus onset (time 0). (B) A heart rate increase reached its peak at four to five beats after the onset of the stimulus (arrowhead) and was then followed by a clear deceleration. No group difference was found (p > 0.05 for both stages, ANOVA). Filled circles, SB patients (n = 8); open circles, normal subjects (n = 8). Data were presented as mean ± SEM.