While the amount of sleep a person truly needs remains up for debate, the effects of not getting enough, both on the mind and the body, are clear to see. Although, it seems we still have a lot to learn on the subject, a message hammered home by a startling new study. People who have been deprived of sleep are much more likely to sign a false confession than those who have had an undisturbed night of rest.

Alongside bolstering the idea that people in a sleep-deprived state might be more susceptible to the influence of suggestion, the study has obvious and perhaps worrying implications for police interrogation of crime suspects. In addition, the work helps in the painting of a more comprehensive picture of sleep deprivation’s effects on cognitive skills and therefore brain function.

“A number of studies have consistently found that there are dramatic changes in the brain with sleep deprivation,” lead researcher Kimberly Fenn from Michigan State University (MSU) told IFLScience. “One of the strongest effects seems to be a reduction in the activity of the frontal lobes, which are important for complex cognition and decision making. I think these changes are possibly mediating the effects that we see with sleep deprivation.”

Implicated in as many as 25 percent of cases, false confessions – an innocent person admitting guilt – are a serious and complex subject. With interrogations often occurring during sleep hours, and some officers even using sleep deprivation to assist interrogation, studies examining the effects this could be having on suspects are justified. 

For this particular investigation, published in PNAS, Fenn and MSU colleagues recruited 88 volunteers and had them complete computer-based tasks and questionnaires during three laboratory sessions, spread over a week. Participants were monitored and repeatedly told not to press the “escape” button on the keyboard as that would lose all of their data.

The night before the last day, half the participants slept for eight hours in lab bedrooms while the others were kept awake. Although that may not reflect most situations during interrogation, Fenn justified this approach.

“In the real world it’s rare that people stay awake for a full night,” she said. “However, it’s common for people to get insufficient sleep over multiple nights.

“The important thing is that pretty much every physiological and cognitive effect seen after one night of sleep deprivation is also seen after a couple of nights of sleep restriction.”

^{Sleep deprivation has been linked with distorted memories of past events. Photographee.eu/Shutterstock}

Before participants were allowed to leave at the end of the study, they were given a form that summarized their activities and falsely accused them of hitting the escape key, which they were asked to confirm for accuracy and sign. Startlingly, while only 18 percent of the rested participants signed the false allegation, half of those who were sleep deprived did. When asked a second time, the figures bumped up to 39 and 68 percent, respectively. In addition, those who scored high on a widely used sleepiness scale were significantly more likely to sign the document.

Another intriguing find was that those with the lowest scores on the Cognitive Reflection Test, which assesses the ability to suppress intuition and respond in a reflective way, were also more likely to falsely confess. Why exactly this is remains unclear, although Fenn predicts that those with lower cognitive abilities may be more susceptible to the effects of sleep deprivation.

Whether or not this study will have an impact on the criminal justice system remains to be seen. Nevertheless, in light of the findings the authors recommend that assessments of sleepiness should be made before interrogations.