Effects of passive heat stress and recovery on human cognitive function: An ERP study

Emerging effects of temperature on human cognition, affect, and behaviour

Human body core temperature is tightly regulated within approximately 37 °C. Global near surface temperature has increased by over 1.2 °C between 1850 and 2020. In light of the challenge this poses to human thermoregulation, the present perspective article sought to provide an overview on the effects of varying ambient and body temperature on cognitive, affective, and behavioural domains of functioning. To this end, an overview of observational and experimental studies in healthy individuals and individuals with mental disorders was provided. Within body core temperature at approximately 37 °C, relatively lower ambient and skin temperatures appear to evoke a need for social connection, whereas comparably higher temperatures appear to facilitate notions of other as closer and more sociable. Above-average ambient temperatures are associated with increased conflicts as well as incident psychotic and depressive symptoms, mental disorders, and suicide. With mild hypo- and hyperthermia, paradoxical effects are observed: whereas the acute states are generally characterised by impairments in cognitive performance, anxiety, and irritability, individuals with depression experience longer-term symptom improvements with treatments deliberately inducing these states for brief amounts of time. When taken together, it has thus become clear that temperature is inexorably associated with human cognition, affect, and (potentially) behaviour. Given the projected increase in global warming, further research into the affective and behavioural sequelae of heat and the mechanisms translating it into mental health outcomes is urgently warranted.

Co-administration of Nanowired Oxiracetam and Neprilysin with Monoclonal Antibodies to Amyloid Beta Peptide and p-Tau Thwarted Exacerbation of Brain Pathology in Concussive Head Injury at Hot Environment

Environmental temperature adversely affects the outcome of concussive head injury (CHI)-induced brain pathology. Studies from our laboratory showed that animals reared at either cold environment or at hot environment exacerbate brain pathology following CHI. Our previous experiments showed that nanowired delivery of oxiracetam significantly attenuated CHI-induced brain pathology and associated neurovascular changes. Military personnel are the most susceptible to CHI caused by explosion, blasts, missile or blunt head trauma leading to lifetime functional and cognitive impairments affecting the quality of life. Severe CHI leads to instant death and/or lifetime paralysis. Military personnel engaged in combat operations are often subjected to extreme high or low environmental temperature zones across the globe. Thus, further exploration of novel therapeutic agents at cold or hot ambient temperatures following CHI are the need of the hour. CHI is also a major risk factor for developing Alzheimer's disease by enhancing amyloid beta peptide deposits in the brain. In this review, effect of hot environment on CHI-induced brain pathology is discussed. In addition, whether nanodelivery of oxiracetam together with neprilysin and monoclonal antibodies (mAb) to amyloid beta peptide and p-tau could lead to superior neuroprotection in CHI is explored. Our results show that co-administration of oxiracetam with neprilysin and mAb to AβP and p-tau significantly induced superior neuroprotection following CHI in hot environment, not reported earlier.

Accuracy of an estimated core temperature algorithm for agricultural workers

There is a substantial burden of occupational health effects from heat exposure. We sought to assess the accuracy of estimated core body temperature (CBT_est) derived from an algorithm that uses sequential heart rate and initializing CBT,¹ compared with gastrointestinal temperature measured using more invasive ingestible sensors (CBT_gi), among outdoor agricultural workers. We analyzed CBT_est and CBT_gi data from Washington State, USA, pear and apple harvesters collected across one work shift in 2015 (13,413 observations, 35 participants) using Bland Altman methods. The mean (standard deviation, range) CBT_gi was 37.7 (0.4, 36.5-39.4)°C. Overall CBT bias (limits of agreement) was -0.14 (±0.76)°C. Biases ranged from -0.006 to -0.75 °C. The algorithm, which does not require the use of ingestible sensors, may be a practical tool in research among groups of workers for evaluating the effectiveness of interventions to prevent adverse occupational heat health effects.

Psychological, Physical, and Heat Stress Indicators Prior to and after a 15-Minute Structural Firefighting Task

Firefighters work in strenuous conditions for prolonged periods wearing up to 20 kg of personal protective equipment. This often contributes to significant heat and cardiovascular strain. This study examined the relationships between psychological and physical measures taken prior to undertaking a 15 min firefighting task, and the occurrence of heat stress and high levels of fatigue following the task. Nine qualified firefighters completed a 15 min “live burn” scenario designed to mimic a fire started by a two-seater couch in a lounge room and completed simulated tasks throughout the duration. Logical reasoning, speed and accuracy, general motivation and fatigue, and physical and mental effort were recorded pre-scenario, and at 0- and 20-min post-scenario. General motivation and fatigue scores at 0- and 20-min post-scenario were highly correlated with each other (rs = 0.90; p = 0.001). The general motivation and fatigue scores, at 0- and 20-min post-scenario, were also strongly related to pre-task logic/reasoning test scores (Post 0 rs = −0.77, p = 0.016; Post 20 rs = −0.87, p = 0.002). Firefighters with lower logical reasoning and speed and accuracy scores were more susceptible to fatigue and impaired cognition when exposed to rises in core temperature and heat stress.