Effects of heat stress on visual attention network: a functional MRI study

Objective: To investigate the effect of passive hyperthermia on attention network with the event-related functional magnetic resonance imaging (fMRI). Methods: Thirty participants were randomly divided into 2 groups (hyperthermia group and control group). They performed the attention network test (ANT) with event-related IMRI in a hot (50 ℃ and 40% relative humidity) or neutral (20 ℃ and 40% relative humidity) environment, respectively. The network scores were analyzed using a multivariate analysis (MANOVA) within the GLM package, with group as the fixed factor. Univariate post-hoc tests with Tukey corrections for multiple comparisons were used to investigate group differences on each of the three networks. The fMRI data were realigned, normalized and then smoothed with 6 mm FWHM kernel. The fMRI results of the three attention networks were compared between the hyperthermia and the control groups using a two-sample t-test respectively with SPM8. The statistical maps were generated with an integrated threshold at a corrected level of P < 0.05. Results: The behavioral results showed that heat stress enlarged the scores of the executive network [(82.56 ± 20.89) ms vs (58.55 ± 8.96) ms, F = 16.683 < 0.01], but showed no effect on the alerting and orienting networks (P > 0.05). The fMRI results showed that: (i) heat stress enhanced the activity in the right superior frontal gyrus (voxel number =39, t = 3.02, P < 0.01) and depressed the activity in the right middle occipital gyrus, left inferior parietal lobule and left culmen (voxel number = 49, 86, 97; t = -2.86, -3.69, -2.72; and P < 0.01, respectively) in the alerting network, (ii) heat stress enhanced the activity in the temporal lobe (voxel number =29, 58; t = 5.00, 4.57; and P < 0.01, respectively) and depressed the activity in the frontal lobe, parietal lobe and occipital lobe (voxel number = 29-85; t = -5.4--2.61; and P < 0.01, respectively) in the orienting network, and (iii) heat stress enhanced the activity in the dorsolateral prefrontal cortex (voxel number = 35, 58; t = 2.99, 3.10; and P < 0. 01 for the left or right dorsolateral prefrontal cortex, respectively) but not affected the activity in the anterior cingulate. Conclusions: Heat stress impaired the executive function, especially the efficiency of resolving conflict. The negative effects of heat stress on alerting and orienting were overcome by variant regional brain activation. (authors)