Page 120 - 《运动与健康科学》(英文)2024年第2期

TaggedAPTARAEnd242 X.R. Tan et al.
after passive hyperthermia. This could be a physiological due to the efficient thermoregulatory responses in humans and
defense mechanism where perfusion is redistributed to critical the cold temperature of the scanner room. The observed func-
brain areas involved in thermoregulatory behavior, such as the tional deficits would likely be exacerbated if T re was further
52
thalamus, insula, and cingulate cortex. TaggedAPTARAEnd elevated. Second, the participants lost modest amounts of
TaggedAPTARAPCognition was also altered by hyperthermia, specifically the body fluids due to sweating (<3% body mass loss) during the
domains of selective attention and executive function. Execu- scan. Ingestion of water during MRI scan is complicated to
tive function here refers to a set of cognitive processes and execute as the drinking action would introduce unnecessary
mental skills crucial for the cognitive control of behavior such noise; hence, no fluids were provided. Nonetheless, the post-
as (but not limited to) working memory, cognitive flexibility, scan serum osmolality was only marginally above
attentional control, and inhibitory control. 53 The latter 2 295 mOsmol/kg, indicating a minor contribution (if any) of
components were assessed with the Stroop task in this study. dehydration to the results. In this study, only male participants
During the Stroop task, reaction times were quicker with were recruited, and thus it is pertinent to consider that there
induced hyperthermia. Higher muscle temperatures can could be sex differences in brain properties and function 60,61
improve muscle contractility due to its thermal dependence, 54 that may modulate differential brain responses to heating.
thus facilitating faster response times. A hyperthermic state Last, the difficulty of replicating dynamic exercise within
could also have contributed to anxiety and discomfort, which the scanner restricts our ability to investigate neural
may have prompted quicker responses. Despite faster reaction changes at the “point of fatigue” in a realistic exercise
times, task accuracy was not compromised in EX and CL setting.TaggedAPTARAEnd
trials, indicating that executive control was well-preserved
under exertional hyperthermia. The absence of cognitive defi-
TaggedAPTARAH15. ConclusionTaggedAPTARAEnd
cits in exertional trials could be attributed to the elevated
arousal brought about by exercise, which benefits cognition. 55 TaggedAPTARAPOur study demonstrated for the first time that resting T br is
In contrast, the faster reaction time in PA trials was coupled regulated in a narrower homeostatic range than T re , which was
with a lowered task accuracy specific to incongruent stimuli. disrupted by hyperthermia. Importantly, we also showed that
Given that the task accuracy for congruent stimuli was main- this led to the suppression of motor cortical activity and
tained, attentional capacity was likely preserved, but the ability impaired inhibitory control in humans. This emphasizes the
to resolve conflict related to Stroop interference was compro- vulnerability of the human brain to heat stress and highlights
mised. Moreover, the response times were quicker, suggesting the importance of future strategies to lower or maintain T br
an absence of speedaccuracy trade off (i.e., slower response within an optimal range for the preservation of neural function.
times to ensure accuracy). This could be due to aberrant deci- Furthermore, the identified brain regions with neural changes
sion-making or a deficit in response inhibition. Shibasaki may be exploited for early detection of over-exertion under
et al. 56 reported similar findings where passive heat exposure heat (e.g., detecting heat-deficit signatures with wearable
62
led to an increased error rate in a Go/No-go task, suggesting devices using functional near-infrared spectroscopy ). Poorer
an impairment in executive function. In real-world settings, executive function under passive heat exposure is particularly
this reduced inhibitory control could result in a greater likeli- relevant to occupational settings where heat strain may impair
hood of work-related errors or unsafe work behavior when decision making, thereby causing occupational hazards.
workers experience high heat strain from excessive heat expo- Limiting the increase in body temperature with a preemptive
sure. In contrast, it could be possible that manual workers who cooling measure (ice ingestion) is a viable strategy for
carry out exertional work under heat may be less affected preventing heat-related deficits. This study enhances our
cognitively and, instead, may benefit from enhanced reaction understanding of cerebral responses to heat stress, paving the
way for the development of novel heat mitigation strategies
time.TaggedAPTARAEnd
TaggedAPTARAPThe Stroop task-activated brain regions (e.g., medial frontal and better heat management in sporting and occupational
gyrus, inferior prefrontal areas, parietal cortex) were similar to settings.TaggedAPTARAEnd
those found in other MRI studies. 57,58 Increased bilateral supe-
rior-temporal sulcus activity during the post scans in CL trials
TaggedAPTARAH1AcknowledgmentsTaggedAPTARAEnd
could be due to the heightened arousal induced by exercise
that was less counteracted by heat strain. Nonetheless, there TaggedAPTARAPWe would like to thank the participants for their efforts and
was no functional gain from the increase in BOLD activity, as commitment to the study and the radiographers and nurses for
indicated by the unaltered Stroop task performance. When their rendered assistance in MRI scans. We thank Ivan Teng
comparing PA to CT post scans (incongruent vs. congruent Po Wen for his invaluable help with the design and conduct of
stimuli), the left hemispheric lateral occipital cortex was less Stroop Test during the fMRI scans. We express our sincere
active in PA trials. This region corresponds to Brodmann Area gratitude to the students (Lemuel Teo Wei En, Yuen Wing
19 (V3/V3a), which is thought to be linked with visual Yee, and Tan Shi Pei) who helped with the conduct of trials
fatigue. 59 Thus, a possible deficit in visual processing of and the collection of data. This research was supported by
Defence Innovative Research Program (DIRP) Grant (PA No.
stimuli could partially account for the reduced task accuracy.TaggedAPTARAEnd
TaggedAPTARAPSeveral limitations in this study should be noted. Firstly, a 9015102335) from Defence Research & Technology Office,
higher T re (>38.5˚C) could not be maintained during the scans Ministry of Defence, Singapore.TaggedAPTARAEnd