Effects Of Environmental Sleeping Conditions And Next Day Cortisol And Copeptin On Cognition

PURPOSE: Elevated morning concentrations of cortisol and copeptin are associated with poor executive function, but the influence of these hormones on cognitive function (cognitive inhibition domain [i.e., response inhibition and interference control]) following sleep in a hot environment is not known. This study examined the influence of sleep environment on cortisol and copeptin and their effect on cognitive inhibition (CI). METHODS: Ten healthy adults (female, n = 1; age, 25 ± 4y; height, 177.9 ± 7.4 cm; body mass, 75.8 ± 13.8 kg; body fat, 13.5 ± 7.1%) completed two nights of in-laboratory assessments while sleeping in temperate (TTEMP, 25 °C, 30% RH) and hot (THOT, 30 °C, 30% RH) environmental conditions. Upon awakening, blood was collected to examine serum copeptin (SCOP), and salivary samples were collected at 0, 30, and 45 minutes post-awakening, and the greatest morning cortisol concentration (CPEAK) was used. CI was assessed via the Stroop Color Word Task with inhibitory control (measured by inverse incongruency and inverse congruency) reflecting participants’ ability to resist distractions and respond faster to stimuli, indicating better cognitive performance. Paired samples t-tests evaluated between-condition differences in hormones and environmental conditions on CI. Linear mixed models assessed the effect of hormones and environmental conditions on CI. RESULTS: Hormone concentrations did not differ between conditions (mean ± SD [collapsed across conditions]), SCOP, 8.77 ± 3.13 pmol/L (p = 0.90); CPEAK, 21.83 ± 5.62 ng/mL (p = 0.86). There were no differences in CI across conditions when measured by inverse incongruency (MD [95% CI], -27.73 ms [-107.88, 52.42], p = 0.45) or inverse congruency (8.29 ms [-38.18, 54.78], p = 0.69). When controlling for environmental conditions, higher CPEAK was associated with reduced CI (β = -8.68 [95%CI, -14.71, -2.54], p = 0.02) however, there was no significant effect of SCOP on CI (p = 0.91). CONCLUSIONS: Higher CPEAK following a bout of sleep in a hot environment were associated with better incongruency scores, or an ability to display interference control and resist distractions during a CI task. Changes in environmental sleeping conditions did not affect CI the next morning, however, the effect of CPEAK on this response requires further exploration.