demonstrated that it is possible to distinguish between eustress and distress by sAA levels because the sAA level rapidly increases while participants perform a stress-inducing task. Another study found the brain’s electrical activity in the frontal and central lobes in identifying eustress and distress, but this was not proven.īiomarkers, such as salivary alpha-amylase (sAA), are widely used and have been fully proven in the field compared to neuroimaging. One study classified common stress and eustress by heart rate and survey data, showing an accuracy of up to 71% using correlation and principal component analysis. However, some studies have recently attempted to subdivide stress. According to the inverted U-shaped Yerkes–Dodson model, eustress can yield high task accuracy and fast reaction times, whereas distress can not do so.ĭespite the opposite characteristics of both types of stresses, most stress-related neuroimaging studies have not distinguished between eustress and distress. Moreover, it is difficult to divide stress into two different categories: positive-type stress, named as “eustress,” which has a low-stress level/a high behavioral result, and negative-type stress, called “distress,” which has a high-stress level/a relatively low behavioral result. ĭespite the existence of neuroimaging technologies to quantify stress, evaluating stress still remains a challenge because of the lack of evidence for brain hemodynamic activities in stressful people. By taking advantage of these characteristics, the stress level can be easily quantified by the concentration changes of oxygenated hemoglobin (ΔHbO), reduced oxygenated hemoglobin (ΔHbR), and total hemoglobin (ΔHbT) from hemodynamic oscillations. Additionally, brain hemodynamic responses acquired by fNIRS not only exhibit apparent differences between stressful tasks and rest states but also facilitate stress detection and diagnosis. Physically, fNIRS has the advantage of being more accessible and convenient than other devices. įunctional near-infrared spectroscopy (fNIRS) is a state-of-the-art optical neuroimaging technique based on near-infrared biosensors that are used to identify stress levels. The target effect has already been fully demonstrated in many neuroimaging studies. Specifically, the target effect refers to the increase in the intensity of biosignals while looking for intermittently given TS. This phenomenon is known as the target effect. Some studies have often reported high amplitudes of positive or negative hemodynamic signals in stressed people using target images. The process of finding positive or negative images of TS not only increases people’s attention but also elicits momentary mental stress responses. A stimuli-response task is a representative stress protocol in which one responds to warning stimuli (WS) followed by target stimuli (TS) using emotional international affective picture system (IAPS) images. Traditional stress protocols are used to evaluate stress precisely. Brain neurologists focusing on mental stress follow stress protocols to obtain distinct brain images. The number of studies on stress, including diagnosis, detection, and rehabilitation, has gradually increased and thus attracted attention from many researchers. Stress is rapidly becoming one of the most common mental disorders in modern society. We built a foundation for subdividing stress groups into eustress and distress groups using fNIRS. LIS values were larger in the order of the eustress, control, and distress groups this indicates that the stress group can be divided into eustress and distress groups. Specifically, the eustress group exhibited the largest brain activity, whereas the distress group exhibited recessive brain activity, regardless of positive or negative stimuli. Both the stress groups exhibited brain activity in the right frontal cortex. We calculated the laterality index for stress (LIS) from the measured signals to identify the dominantly activated cortex in both the subgroups. We compared the two stress subgroups categorized by sAA using a newly designed emotional stimulus-response paradigm with an international affective picture system (IAPS) to enhance hemodynamic signals induced by the target effect. The stress group was screened by salivary alpha-amylase (sAA) and then, the brain’s hemodynamic reactions were measured by functional near-infrared spectroscopy (fNIRS) based on the near-infrared biosensor. We aimed to ascertain the necessity of subdividing the stress groups. However, it is challenging because of the inconsistent pattern in brain activation. A stress group should be subdivided into eustress (low-stress) and distress (high-stress) groups to better evaluate personal cognitive abilities and mental/physical health.
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