Effects of sleep restriction and light intensity on mental effort during cognitive challenge

We investigated the effects of sleep duration and light intensity on effort-related cardiovascular response. We predicted that due to reduced alertness after shortened sleep duration perceived task demand should increase which should lead to higher mental effort. Similarly, lower light intensity should also lead to lower alertness, and therefore to higher perceived task demand and therefore higher effort. Effort was operationalized as sympathetic beta-adrenergic impact on the heart and assessed through reactivity of the cardiac pre-ejection period (PEP) and systolic blood pressure (SBP). Twenty-four healthy volunteers underwent two experimental sessions, one after 5 and one after 8 h of sleep opportunity in a counterbalanced order (within-person). Experimental lighting conditions (100 lx vs. 500 lx, within-person) were applied for 15 min, and for following 5-min modified auditory Sternberg task. In line with our hypothesis, results showed a stronger SBP (and DBP) reactivity after sleep restriction (ps < 0.001), indicating higher effort exertion. Contrary to our prediction, 500 lx light led to higher PEP reactivity compared to 100 lx (p = 0.032). Overall, our results provide the first experimental evidence that shorter sleep duration leads to higher mental effort.