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Habitual Sleep Duration
The number of hours of sleep a person gets each night contributes to how alert a person will feel when awake.  Over time, “chronic partial sleep deprivation” can impair performance as much as going a full 24 hours or more without any sleep at all.  In addition, habitual nightly sleep duration is directly correlated to one’s ability to learn new tasks.

Graph showing performance decrements on a simple reaction time task with sleep restricted to 4, 6, or 8 hr. performance is worst under the 4 hr condition

Figure taken from Van Dongen 2003

 The figure to the left shows the results of an experiment conducted by Van Dongen and colleagues. Subjects were restricted to 4, 6, or 8 hours of sleep per night over a two week period. Subjects completed regular testing batteries which included the psychomotor vigilance task (PVT) to assess reaction time in each of the conditions. The authors found a linear increase in performance lapses in all conditions. While sleep restriction of 4 hours per night was found to be the worst, after 14 days of restriction, both the 4 and 6 hour partial sleep deprivation conditions reached performance

decrements equivalent to 44-62 hours of total sleep deprivation (TSD) (Van Dongen 2003).

While sleep restriction of 4 hours per night was found to be the worst, after 14 days of restriction, both the 4 and 6 hour partial sleep deprivation conditions reached performance decrements equivalent to 44-62 hours of total sleep deprivation (TSD) (Van Dongen 2003).

In a study conducted by Stickgold and colleagues (Figure to the right), subjects were tested using a visual discrimination task to assess learning and memory consolidation.

Figure showing lack of retention of a memory task with sleep loss
Figure taken from Stickgold 2000
 

The control group (shown in the black bars) was tested at baseline and then each subsequent day. The control subjects steadily improved on performance of the task over the course of four days. The experimental group of subjects were tested at baseline, but were not allowed to sleep until 9:00 PM on the day following the initial training. This group was tested again on day 3 (the white bar). The sleep deprived group performed significantly worse on the task compared to the control group, suggesting that even a single night of sleep loss can impair learning days later (Stickgold 2000).

Memory consolidation and learning is a critical component to the mission of all teaching hospitals.  Demanding schedules coupled with the demands of life often drastically reduce the number of hours of sleep housestaff can get on a regular basis.  This chronic sleep deprivation can take an enormous toll in the ability of young residents to learn while on duty. Modified schedules can often increase the number of hours available for sleep each night as well as the number of hours available for recovery of sleep following acute sleep deprivation.