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

Abstract

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°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.

Keywords: aging; cognitive function; hyperthermia; thermal comfort.

Copyright © 2015 the American Physiological Society.

Figures

Fig. 1.

Internal temperature during cognitive testing in younger (n = 14) and older (n = 15) subjects during heat stress and time control trials at baseline (left) and during heat stress (i.e., heat) and following a time control period (i.e., control; right). Top: temporal changes in internal temperature across the six cognitive tests independent of the test being undertaken. Bottom: internal temperature during each cognitive test. Data are presented as means ± SD. VAS, visual analog scales; CRT, choice reaction time test; RVP, rapid visual processing test; PRM, pattern recognition memory test, SSP, spatial span test; OTS, one touch stockings of Cambridge test. ∝Significantly different from time control trial (P < 0.001). ϕSignificant increase over time (P < 0.001).

Fig. 2.

Performance on tests evaluating aspects of attention in younger (n = 14) and older (n = 15) subjects during heat stress and time control trials at baseline and during heat stress (i.e., heat) and following a time control period (i.e., control). Left: rapid visual processing test (RVP). Right: choice reaction time test (CRT). Data are presented as means ± SD. *Significantly different from younger within trial(s) at same time point(s) (P ≤ 0.003). †Significantly different from baseline within trial and age group (P ≤ 0.001).

Fig. 3.

Performance on tests evaluating aspects of memory in younger (n = 14) and older (n = 15) subjects during heat stress and time control trials at baseline and during heat stress (i.e., heat) and following a time control period (i.e., control). Top: spatial span test (SSP). Bottom: pattern recognition memory test (PRM). Data are presented as means ± SD. *Significantly different from younger within trial(s) at same time point(s) (P < 0.001).

Fig. 4.

Perceptual indices in younger (n = 14) and older (n = 15) subjects during heat stress and time control trials at baseline and during heat stress (i.e., heat) and following a time control period (i.e., control). Data are presented as means ± SD. *Significantly different from younger within trial at same time point (P = 0.049). †Significantly different from baseline within trial and age group (P ≤ 0.028). ∝Signifcantly different from time control trial at same time point (P ≤ 0.027).