Cognitive and perceptual responses during passive heat stress in younger and older adults

We tested the hypothesis that attention, memory, and executive function are impaired to a greater extent in passively heat-stressed older adults than in passively heat-stressed younger adults. In a randomized, crossover design, 15 older (age: 69 +/- 5 yr) and 14 younger (age: 30 +/- 4 yr) healthy subjects underwent passive heat stress and time control trials. Cognitive tests (outcomes: accuracy and reaction time) from the CANTAB battery evaluated attention [rapid visual processing (RVP), choice reaction time (CRT)], memory [spatial span (SSP), pattern recognition memory (PRM)], and executive function [one touch stockings of Cambridge (OTS)]. Testing was undertaken on two occasions during each trial, at baseline and after internal temperature had increased by 1.0 +/- 0.2 degrees C or after a time control period. For tests that measured attention, reaction time during RVP and CRT was slower (P <= 0.01) in the older group. During heat stress, RVP reaction time improved (P <= 0.01) in both groups. Heat stress had no effect (P >= 0.09) on RVP or CRT accuracy in either group. For tests that measured memory, accuracy on SSP and PRM was lower (P <= 0.01) in the older group, but there was no effect of heat stress (P >= 0.14). For tests that measured executive function, overall, accuracy on OTS was lower, and reaction time was slower in the older group (P <= 0.05). Reaction time generally improved during heat stress, but there was no effect of heat stress on accuracy in either group. These data indicate that moderate increases in body temperature during passive heat stress do not differentially compromise cognitive function in younger and older adults.