Incident experience predicts freezing-like responses in firefighters

Freezing is a defensive response to acute stress that is associated with coping and alterations in attentional processing. However, it remains unclear whether individuals in high risk professions, who are skilled at making rapid decisions in emergency situations, show altered threat-induced freezing. Here we investigated the effect of incident experience in a high risk profession on freezing. Additionally, we explored whether any effect of incident experience on freezing would be different for profession-related and -unrelated threat. Forty experienced and inexperienced firefighters were presented neutral, pleasant, related-unpleasant, and unrelated-unpleasant pictures in a passive viewing task. Postural sway and heart rate were assessed to determine freezing. Both postural and heart rate data evidenced reduced freezing upon unpleasant pictures in the experienced versus the inexperienced group. Relatedness of the unpleasant pictures did not modulate these effects. These findings indicate that higher incident experience relates to decreased threat-induced freezing, at least in a passive task context. This might suggest that primary defense responses are malleable through experience. Finally, these findings demonstrate the potential of using animal to human translational approaches to investigate defensive behaviors in relation to incident experience in high risk professions and stimulate future research on the role of freezing in resilience and coping

Time perception and timed decision task performance during passive heat stress

This study investigates the hypotheses that during passive heat stress, the change in perception of time and change in accuracy of a timed decision task relate to changes in thermophysiological variables gastrointestinal temperature and heart rate (HR), as well as subjective measures of cognitive load and thermal perception. Young adult males (N = 29) participated in two 60-min head-out water immersion conditions (36.5°C-neutral and 38.0°C-warm). Cognitive task measurements included accuracy (judgment task), response time (judgment ask), and time estimation (interval timing task). Physiological measurements included gastrointestinal temperature and heart rate. Subjective measurements included cognitive task load (NASA-TLX), rate of perceived exertion, thermal sensation, and thermal comfort. Gastrointestinal temperature and HR were significantly higher in warm versus neutral condition (gastrointestinal temperature: 38.4 ± 0.2°C vs. 37.2 ± 0.2°C, p < 0.01; HR: 105 ± 8 BPM vs. 83 ± 9 BPM, p < 0.01). The change in accuracy was significantly associated with the change in gastrointestinal temperature, and attenuated by change in thermal sensation and change in HR (r2=0.40, p< 0.01). Change in response time was significantly associated with the change in gastrointestinal temperature (r2=0.26, p< 0.002), and change in time estimation was best explained by a change in thermal discomfort (r2=0.18, p< 0.01). Changes in cognitive performance during passive thermal stress are significantly associated with changes in thermophysiological variables and thermal perception. Although explained variance is low (<50%), decreased accuracy is attributed to increased gastrointestinal temperature, yet is attenuated by increased arousal (expressed as increased HR and warmth thermal sensation)

Time perception and timed decision task performance during passive heat stress

This study investigates the hypotheses that during passive heat stress, the change in perception of time and change in accuracy of a timed decision task relate to changes in thermophysiological variables gastrointestinal temperature and heart rate (HR), as well as subjective measures of cognitive load and thermal perception. Young adult males (N = 29) participated in two 60-min head-out water immersion conditions (36.5°C-neutral and 38.0°C-warm). Cognitive task measurements included accuracy (judgment task), response time (judgment ask), and time estimation (interval timing task). Physiological measurements included gastrointestinal temperature and heart rate. Subjective measurements included cognitive task load (NASA-TLX), rate of perceived exertion, thermal sensation, and thermal comfort. Gastrointestinal temperature and HR were significantly higher in warm versus neutral condition (gastrointestinal temperature: 38.4 ± 0.2°C vs. 37.2 ± 0.2°C, p < 0.01; HR: 105 ± 8 BPM vs. 83 ± 9 BPM, p < 0.01). The change in accuracy was significantly associated with the change in gastrointestinal temperature, and attenuated by change in thermal sensation and change in HR (r2=0.40, p< 0.01). Change in response time was significantly associated with the change in gastrointestinal temperature (r2=0.26, p< 0.002), and change in time estimation was best explained by a change in thermal discomfort (r2=0.18, p< 0.01). Changes in cognitive performance during passive thermal stress are significantly associated with changes in thermophysiological variables and thermal perception. Although explained variance is low (<50%), decreased accuracy is attributed to increased gastrointestinal temperature, yet is attenuated by increased arousal (expressed as increased HR and warmth thermal sensation)

Grand average alpha modulation.

<p>Average alpha modulation over all conditions (easy near, easy far, difficult near, difficult far) and subjects (N = 14) in the period between 1 s and 2.5 s after cue onset. Crosses indicate sensors with an alpha modulation that deviate significantly from zero (p<0.05). These highlighted sensors define the ROIs (one in each hemisphere) used in the alpha power and alpha time-power analyses. Note that the small gap in the left ROI is due to sensor dropout.</p

Mean and standard error of mean per stimulus category of the freezing measures and the subjective ratings presented for the experienced (<i>n</i> = 19) and inexperienced (<i>n</i> = 16) group separately.

<p>Mean and standard error of mean per stimulus category of the freezing measures and the subjective ratings presented for the experienced (<i>n</i> = 19) and inexperienced (<i>n</i> = 16) group separately.</p

Classification rate of alpha power.

<p>Single-trial classification rate of alpha power in task-relevant sensors for each condition (easy near, easy far, difficult near, difficult far). Markers indicate individual subject classification rates whereby each unique marker (combination of colour and shape) represents the same subject. Bold markers indicate a classification performance significantly above chance level (p<0.05). On average a classification rate of 63.5% was reached (chance level is 50%). A significant difference was found between task difficulty levels; Classification rate was on average 61.1% in the easy condition and 65.9% in the difficult condition (p<0.05).</p

Behavioural accuracy (A) and response time (B) in the discrimination task.

<p>Bars show grand average behavioural accuracy as percentage correct (A) and grand average response time in seconds (B) within each condition (easy near, easy far, difficult near, difficult far). Markers indicate individual subject averages where each unique marker (combination of colour and shape) represents the same subject. On average subjects were less accurate with longer response times in the difficult conditions than in the easy conditions. No significant differences were found between behavioural accuracy or response time in the near and far spatial attention conditions for equal difficulty level.</p