Ultradian cognitive performance rhythms during sleep deprivation

Ultradian rhythms that modulate daytime human behavior and cognitive performance exist. However, their subtleness may make them susceptible to masking effects from heightened arousal, attention, and motivation. Experimental designs using sleep attenuation and total sleep-deprivation appear to unmask certain ultradian rhythms. This chapter reviews the few studies designed to evaluate rhythms in waking EEG and task performances during sleep deprivation. Some EEG studies demonstrate an approximate 90-min rhythm in arousal. No confirmation has been reached for an underlying common basic rest-Activity cycle (BRAC) that ties the phases of the nightly 90-min NREM-REM sleep cyclicity to those of any ensuing similar-period wake time alertness and performance rhythms. Studies have also found a slower 4-h rhythm. Other arousal and performance rhythms shorter than 90 min and longer than 4h have been suggested, but are not as well substantiated. The 90-min and 4-h rhythms seem to dominate the morning and early afternoon circadian rhythm portion during wakefulness, but are attenuated later by the rising circadian rhythm, or perhaps other slower ultradian cycles. Ultradian rhythm expression appears related to a greater susceptibility for reduced arousal and sleepiness. Impairment of cognitive-behavioral performance occurs at times of low circadian influences and increased ultradian fluctuations. These effects, in combination with any amount of sleep deprivation, raise concerns about naturally occurring potentially widespread performance decrements. Concern stems from the widespread increase in chronic partial-sleep loss in cultures deliberately abridging adequate nightly sleep in favor of attempting to maintain a 24/7 mode of existence.