Dose-response relationship between sleep duration and human psychomotor vigilance and subjective alertness

Although it has been well documented that sleep is required for human perfo rmance and alertness to recover from low levels after prolonged periods of wakefulness, it remains unclear whether they increase in a linear or asympt otic manner during sleep. It has been postulated that there is a relation b etween the rate of improvement in neurobehavioral functioning and rate of d ecline of slow-wave sleep and/or slow-wave activity (SWS/SWA) during sleep, but this has not been verified. Thus, a cross-study comparison was conduct ed in which dose-response curves (DRCs) were constructed for Stanford Sleep iness Scale (SSS) and Psychomotor Vigilance Task (PVT) tests taken at 1000 hours by subjects who had been allowed to sleep 0 hours, 2 hours, 5 hours o r 8 hours the previous night. We found that the DRCs to each PVT metric imp roved in a saturating exponential manner, with recovery rates that were sim ilar [time constant (T) approximate to 2.14 hours] for all the metrics. Thi s recovery rate was slightly faster than, though not statistically signific antly different from, the reported rate of SWS/SWA decline (T approximate t o 2.7 hours). The DRC to the SSS improved much more slowly than psychomotor vigilance, so that it could be fit equally well by a linear function (slop e -0.26) or a saturating exponential function (T = 9.09 hours). We conclude that although SWS/SWA, subjective alertness, and a wide variety of psychom otor vigilance metrics may all change asymptotically during sleep, it remai ns to be determined whether the underlying physiologic processes governing their expression are different.