Individual variations in awakening times, daytime alertness and somnograms as a function of ad libitum extended sleep

Individual variations in timing of polysomnograms, vigilance, alertness ratings, and wakeful electrocorticograms were investigated after being potentiated by extended sleep. The entire (N = 16) constituency of healthy young adults was dichotomized into subgroups (Ns = 8) whose delayed awakenings occurred before 1045 (0930-1036) and at 1105 (1105-1430) or later. Statistical analyses were applied to determine whether selected dependent variables during ad libitum delayed sleep covaried as a function of the substantial (5-hr) range observed for awakening times. Relative to the rigidly scheduled 8-hr control condition, statistically significant average increases occurred in stage 2, REM sleep and REM cycle length as a function of delayed afternoon awakening times, whereas this proved true for stage 3 during the morning. For all indexes of sleep physiology, there were statistically significant interactions of the ad-libitum extended treatment with arising times. Average elevations in stage 2, REM sleep and REM cycle length were associated with ad libitum sleep which terminated at 1105 or later. By contrast, increases of stage 3 coincided with extended sleep wherein awakenings occurred between 0930 and 1036 in the morning. The average integrated amplitude (microV) of 8-13 Hz alpha rhythm was greater (less cortical alertness), whereas psychometric alertness ratings were significantly less in conjunction with ad libitum delayed morning sleep and among individuals whose awakenings occurred greater than 1100. Finally, sublingual temperature was significantly more elevated within the vicinity of 1105-1430, and this proved true with respect to d', the signal detection index, from 0930 until 1036. Accumulated evidence does indicate that acute variations in sleep patterns contribute to a disturbance in the diurnal cycle most conspicuously during either: (1) morning or (2) when postdormital evaluations of alertness are initially completed. The clinical relevance of these findings for neuropsychiatric states such as idiopathic hypersomnias, bipolar affective illness and depression is explicated.