Dopamine activity can modulate physical performance in the heat, but less is known about its effects on cognition during thermal stress. Twelves males completed a randomized, double-blinded protocol consisting of oral ingestion of 20 mg of methylphenidate (MPH) or placebo (lactose pill) during passive heating using a water-perfused suit (water temperature ~49°C). To identify the impact of peripheral versus central thermal strain, a cognitive test battery was completed at four different thermal states: baseline (BASE; 37.2±0.6˚C core, 32.9±0.7˚C skin), neutral core-hot skin (NC-HS; 37.2±0.3˚C, 37.4±0.3˚C), hyperthermic core-hot skin (HC-HS; 38.7±0.4˚C, 38.7±0.2˚C), and hyperthermic core-cooled skin (HC-CS; 38.5±0.4˚C, 35.1±0.8˚C). The cognitive test battery consisted of the 2-back task (i.e. working memory), set-shifting (i.e. executive function), Groton Maze Learning Task (i.e. executive function) and detection task (i.e. psychomotor processing). MPH led to significantly higher heart rates (~5-15 b·min-1) at BASE, NC-HS, and HC-HS (all p<0.05). There were no significant differences in the number of errors made on each task (all p<0.05). Participants were significantly faster (p<0.05) on the set-shifting task in the HC-HS timepoint, irrespective of drug condition (p>0.05). In summary, we demonstrated that 20 mg of MPH did not significantly alter cognitive function during either normothermia or moderate hyperthermia.
Novelty:
● 20 mg of MPH did not significantly alter cognitive function during passive heat stress
● MPH led to significant higher heart rates (~5-15 bmin-1) in thermoneutral and during passive heat stress
● Future studies are needed to determine the mechanisms of why MPH improves physical but not cognitive performance during heat stress
