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 heatstressed younger adults. In a randomized, crossover design, 15 older (age: 69 Ϯ 5 yr) and 14 younger (age: 30 Ϯ 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 Ϯ 0.2°C or after a time control period. For tests that measured attention, reaction time during RVP and CRT was slower (P Յ 0.01) in the older group. During heat stress, RVP reaction time improved (P Ͻ 0.01) in both groups. Heat stress had no effect (P Ն 0.09) on RVP or CRT accuracy in either group. For tests that measured memory, accuracy on SSP and PRM was lower (P Ͻ 0.01) in the older group, but there was no effect of heat stress (P Ն 0.14). For tests that measured executive function, overall, accuracy on OTS was lower, and reaction time was slower in the older group (P Յ 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. cognitive function; aging; hyperthermia; thermal comfort ADULTS OVER THE AGE OF ϳ65 YR are at an increased risk of illness, injury, hospitalization, and death during heat waves (23, 29, 33-36, 63, 64). Age-related impairments in physiological responses to heat stress undoubtedly contribute to this increased risk (32). Heat-stressed older adults have attenuated increases in skin blood flow (30, 31) and sweating (26, 27), as well as impaired cardiovascular adjustments (42, 43). However, both physiological and psychological states influence health and safety (52, 53). Thus, a variety of factors may mediate the deleterious outcomes observed in the older population during heat waves.Healthy aging is associated with a general cognitive decline (49). Aspects of memory (4, 10, 12), attention (1, 12, 40), executive functioning (12,58,60), and processing speed (59) are typically [but not always (37, 48)] impaired with advancing age. This chronological cognitive decline may contribute to the risk of deleterious outcomes during heat waves in older adults by, for instance, leading to poor decision-making. Interestingly, perhaps because of the deleterious impact of heat stress on cerebral blood flow (46, 61) and/or disruptions in cerebral functional connectivity (66), many cognitive processes are impaired in heat-stressed younger adults [e.g., aspects of attention (19, 22, 65), memory (6, 19, 28, 41, 54), an...

Peer Review #3 of "Obesity, but not hypohydration, mediates changes in mental task load during passive heating in females (v0.1)"

“…These visual and verbal memory impairments are similar to those observed in previous studies (Gaoua, Racinais et al 2011b;Schlader et al 2013). Cognitive function involving greater neuronal resources are impaired to a greater extent during heat stress than less demanding tasks (Hocking et al 2001;Simmons et al 2008;Gaoua et al 2011a;Gaoua, Racinais et al 2011b;Schlader et al 2015) and memory is a more complex task than attention tasks. Baddedly's working memory theory states verbal memory is controlled by the phonological loop, while the "visuospatial sketchpad" controls visual memory (Baddeley et al 1974).…”

Cognitive function and short-term exposure to residential air temperature: A repeated measures study based on spatiotemporal estimates of temperature

“…For example, Schlader et al (2015) observed age-related differences in processing speed, memory, and executive function when comparing elderly subjects to middle-aged subjects. In the sensitivity analysis, we restricted to subjects aged ≥ 70 years and found that the temperature-cognition relationship remained significant and showed a similar shape in those subjects.…”

“…Compared to those in the control condition, people in the hot condition had significant declines in performance on working memory tests, but not on attention tests. In a randomized crossover study that included 15 elderly and 14 middle-aged healthy individuals, passive heat stress, induced by perfusing 48 degrees C water through the suit for 40–60 minutes and sufficient to increase subjects’ internal temperature by 1.0–1.6 degrees C, did not affect performance of cognitive tests on attention, memory, and execution function in either group (Schlader et al, 2015). However, Leavitt et al (2012) reported that warmer outdoor temperature was linked to worse cognitive status (i.e., slowed processing speed and learning/memory problems) in persons with multiple sclerosis in a cross-sectional analysis (No.…”

“…Researchers have examined the relationship between cognitive function and temperature, but the findings are mixed: some found worse cognition related to cold or heat, while others did not observe any change (Leavitt et al, 2012; Muller et al, 2012; O’Brien et al, 2007; Pilcher et al, 2002; Racinais et al, 2008; Schlader et al, 2015). In addition, most of the published work consisted of experimental studies in which the sample size was small and/or only a few specific values of temperature were inspected (Makinen et al, 2006; Muller et al, 2012; Racinais et al, 2008).…”

Motor performance is preserved in healthy aged adults following severe whole-body hyperthermia

“…water bath) or indirect (e.g. water-perfused suit) external heating of older subjects and have focused on the direct effects of mild-tosevere whole-body hyperthermia (WBH) on the kinetics of physiological responses including body temperature [2], sweating efficiency [10], cardiovascular parameters [11,12], metabolic rate [2], heat gain [2,10], subjective sensation [13], and cognition [14]. To our knowledge, the functional consequences of severe WBH (rectal temperature increase from normal !1.5 C; Bain, Nybo [15]) on neurophysiological functions in healthy aged men have not been fully investigated.…”