Overnight Sleep Loss and “Executive” Decision Making—Subtle Findings

Whereas much has been published about the effect of sleep loss on relatively simple tasks highly sensitive to sleepiness, especially under monotonous situations,^1,2 less is known about more complex aspects of behavior, especially decision making and “risky” behaviors concerning “executive thinking” that largely involve the prefrontal cortex (PFC).^3,4 Such skills are likely to be required by managers, physicians, control room operators, the military and emergency services, often early morning during the daily circadian trough, after having being awake for around 20 h during the first night shift.⁴ Especially relevant to those working in international financial markets, often necessitating working through the night, are the latest findings by Libedinsky and colleagues,⁵ described in the current issue of SLEEP, following a series of earlier studies by this group into executive functioning during sleep loss.^6–9 Previously they had noted that, “even a single night of total sleep deprivation can have dramatic effects on economic decision making.”⁹

This latest report by Libedinsky et al. involved a series of rather complex but unique experiments concerning decisions to be made either at 06:00 following 22 h of wakefulness, or at around 08:00 after normal sleep. The unusual feature about this study was that these decisions concerned a future event. Under one scenario, participants could opt for a relatively small financial reward obtainable soon, or choose between larger rewards increasing over a duration of months, but not available until then (i.e., “delay discounting”). The second scenario (i.e., “effort discounting”) involved participants choosing between levels requiring increasing effort (typing increasing numbers of words backwards) but having greater financial rewards. Thus, delay discounting assessed the willingness to have a smaller sum sooner, rather than a larger sum later, whereas effort discounting was the willingness to accept smaller rewards for less effort. A real world analogy, offered by the authors, was the sleep deprived surgeon having to decide on one of two surgical techniques to be adopted for a future operation (when the surgeon would be in a fit and alert state); these being a difficult procedure having a good outcome versus a simper procedure with reasonable outcome.

Although Libedinsky et al.⁵ hypothesized that sleep loss would affect delay discounting, with participants more likely to opt for a “quick buck,” this was not the outcome of their study. Nonetheless, it should be noted that the delays incurred could be very long (months), rather than just a few hours. On the other hand, effort discounting was significantly impaired, which might seem unsurprising at first glance but, again, it must be remembered that it applied to a future event when the participants would be refreshed. The authors reasoned that sleep loss reduced their participants' capability to decide, because they had projected this impairment into the future. However, I suggest that this outcome also involves changes to risk perception, as other evidence indicates that if sleep deprived people believe that they are likely to succeed, then they take greater risks,^6,10,11 or, if they perceive a likely failure, then they become risk averse.^3,10,12,13 Clearly, the perceived uncertainty and the surrounding physical and social circumstances do have a major influence during sleep loss, with decisions becoming more influenced by emotions rather than by rational thought.¹⁴ Also, apart from a loss of insight into one's deteriorating executive skills,¹⁵ there are individual differences in coping with extended wakefulness, especially in terms of personality and cognitive styles.^16,17 Interestingly, people with clock gene polymorphism (PER3 -5/5) associated with extreme morningness, display poorer executive functioning during early morning extended wakefulness.^18,19

Whereas there is some contention over whether executive functions are impaired by sleep loss,²⁰ many such tests only assess limited aspects of the complex range of executive function, often excluding behaviors classed operationally as “higher” or “supervisory” executive functions.²¹ These involve dealing with: novelty, unexpected change, uncertainty, ignoring of conflicting and irrelevant information, tracking of and remembering very recent developments, maintaining focus on key issues, foreseeing and weighing up potential outcomes, and the need to be innovative in planning appropriate responses.

Ideally, to be applicable to the real world, executive tests need to be “ecological” as reflected by Libedinsky's team; albeit an approach adopted by only a few other sleep loss studies.^e.g.,22 More commonly used “non-supervisory” executive tests (e.g., Sternberg working memory, Stroop tests, digit-symbol substitution) incorporate little inherent novelty,²³ especially when presented repeatedly, when the test becomes “routine”^23–25 and “executiveness” is lost. Here, participants often adopt new strategies resulting in faster, more correct responses, thus nullifying ostensible declines from seep loss.²⁵ Another confound is that tests are often of fairly short duration, albeit lasting 10 minutes or so. However, in reality, overnight critical situations can be protracted over longer periods, to the extent that shorter experimental periods may underrate a potential worsening of executive function. This is even more likely to occur in the presence of additional stressors, as studies outside sleep deprivation certainly point to adverse stress effects on executive decisions.²⁶

Even in situations involving frustrating, protracted and delicate discussions during the early morning hours, typically timed for sleep, when, for example sleepless politicians attempt to resolve deadlocks and negotiate terms—other aspects of executive function can be affected,^4,13 with people becoming irritable, obdurate, losing track of when and what was recently said, having difficulty in finding the appropriate (and diplomatic) words,^27,28 being more wary of possible exploitation,¹⁵ and failing to detect subtle facial expressions and otherwise useful nonverbal cues.²⁹

Whereas a short nap,³⁰ caffeine,³¹ and even monetary incentives³² are effective countermeasures to “sleepiness,” such methods as a means for rectifying impaired executive function are less clear,^3,33 especially when there are emotional changes.⁴ Finally, an often overlooked aspect to sleep-related impaired (supervisory) executive thinking, concerns being suddenly and unexpectedly awoken early morning (especially from deep sleep) and confronted with a crisis. At least 20 min seems to be required to overcome inertial effects on the PFC³⁴ and to enable effective supervisory executive decision making.³⁵

CITATION

Horne J. Overnight sleep loss and “executive” decision making—subtle findings. SLEEP 2013;36(6):823-824.

DISCLOSURE STATEMENT

Dr. Horne has indicated no financial conflicts of interest.