LAUSR

The interaction between the circadian clock and sleep drive generates a rhythm of deterioration and recovery in cognition over wake and sleep, respectively. In modern society, our sleep is often disrupted due to long and unsociable work hours. Emerging evidence suggests that this negatively impacts our social interactions, but the physiological mechanisms remain unclear. Our perceptions of other people’s mental states dominate interpersonal interactions, and profoundly impact our lives. This study examined how sleep deprivation impacts our perceptions of another’s mental state (a cognitive domain known as Theory of Mind: ToM). 21 young healthy adults completed the study (11 females: mean age +/-SD =22.09 +/- 3.59, 10 males: mean age +/- SD =23 + 4.13). Over a 12-hour overnight wakefulness period, we examined changes in ToM every two hours with the Reading in the Mind’s Eye (RMIE) task. It consists of 36 images, each a pair of eyes representing an emotion, categorized as Easy or Difficult and as positive, negative, and neutral (valence). We measured accuracy based on a 4-forced alternative response. Subjective sleepiness was measured every two hours with the Karolinska Sleepiness Scale (KSS). Our analysis revealed a significant effect of wakefulness on accuracy (p < 0.0001), such that it declined precipitously 4 hours into the protocol (coinciding with midnight). Accuracy was significantly better (p< 0.01) for Easy stimuli than on Difficult stimuli, but accuracy on both declined significantly with wakefulness. A similar result was seen with valence (p< 0.0001), with Positive stimuli (74.5% +/- 1.8%) showing a better accuracy (mean +/- 1SE) than negative (57.4% +/- 1.9%) and neutral (58.2% +/- 1.7%) ones. But accuracy on all three declined with wakefulness (Positive: 84% -72.4%; Negative:61.2% - 58.5; Neutral: 64.2% - 59.9%). Sleepiness increased significantly overnight (p< 0.0001). Furthermore, there was a significant correlation (correlation: 0.5; Fisher’s z test: p = 0.03) between the change sleepiness and RMIE task accuracy. These findings are one of first descriptions of the circadian and sleep regulation in Theory of Mind, our ability to empathize. They have significant scientific and clinical implications. British Academy/Leverhume Small Research Grant to Nayantara Santhi.