# Effect of Exposure Time on Thermal Behaviour: A Psychophysiological Approach
## 2 Physiology of Thermal Stress  
The decision-making process regarding heat, or its lack thereof, originates from the human body's homeostasis that maintains its core temperature in a very tight range. In humans, the temperature difference between sweating to shivering is estimated to be around 0.68 \({}^{\circ}\)C [14], or more specifically 1.4 \(\pm\) 0.6 \({}^{\circ}\)C for males and 1.2 \(\pm\) 0.5 \({}^{\circ}\)C [15]. It is suggested that this quality was amongst the key events that had helped mammals (and birds) across the globe, in a vast range of temperatures from poles to deserts, to proliferate--which is why it is one of the central mechanisms of our physiology. Based on [PERSON] & [PERSON] [16], thermal satisfaction can be used as a reward in mammals and can motivate them to learn and perform new tasks. This means thermal homeostasis is as strong and driven by the same motivational systems as some other basic functions, like eating and drinking. Thermoregulation can be achieved through behavioural and/or physiological responses [17, 18]. Behavioural responses are conscious and include seeking a more thermally neutral place, changing posture, altering clothing, or making changes in the immediate environment [19]. The thermoregulatory physiological responses of the body's autonomic nervous system mechanisms include regulation of the skin blood flow (vasoconstriction or vasodilation), shivering and sweating (sudomotor activity) [20, 21, 22]. These physiological functions employ a series of body parts, from outer surfaces to the inner core and, in a sense, compose a layered defence system. This system includes specialised warm and cold thermoreceptor sensors that provide feedback and feedforward to the spinal cord [23], which by their afferent activity drives the relevant regulatory system. An interesting difference between the feedback and feedforward sensing system is that feedback receptors are mainly located throughout the body core, including the brain, viscera and spinal cord and evaluate the internal temperature, while the peripheral receptors on the skin act as feedforward mechanisms by sensing the air temperature around them and anticipate the change in the thermal balance It needs to be noted that there is also a debate whether skin should be classified as a feedforward mechanism. For further discussion, please refer to [24]. Finally, it is worth noting that the stimuli do not always originate from the external sources (i.e., climate), but the body itself might be generating excessive heat due to reasons such as high metabolic rate [25], fighting an infectious or viral disease [26] or regular digestion. Behavioural adaptation mechanisms can take on a large portion of the thermoregulatory burden, leaving ideally less work for physiological alterations [27, 28]. This means that the body is subjected to less stress, and can successfully avoid large internal fluctuations in vital organs [29]. While the stress placed on the body to maintain a stable core temperature is crucial, this does not equal subjecting the human body to a constant ambient temperature. While this may feel \"comfortable\", several studies link continuously being in a thermoneutral environment to likeliness of developing obesity, or being susceptible to developing type 2 diabetes [30]. In other words, neither too much stress nor too much comfort is good for human health. Autonomous thermoregulation is mostly part of the Sympathetic Nervous System (SNS) [31], apart from skeletal muscle shivering, which is controlled by the Central Nervous System (CNS) [32] (see Figure 1). The skin, while being the largest sensing organ, is also the medium in which first regulation responses happen, i.e., vasomotor or sudomotor activity. This means the skin is also a good indicator to observe the thermoregulation activity in the body. Electrodermal activity (EDA), referring to the changes in electrical conductance of the skin, is a popular biosignal to observe and quantify exocrine sweat activity controlled by excrine sweat glands [33, 34].