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High resolution thermal infrared imaging is a pioneering method giving indices of sympathetic activity via the contact-free recording of facial tissues (thermal imprints). Compared to established stress markers, the great advantage of this method is its non-invasiveness. The goal of our study was to pilot the use of thermal infrared imaging in the classical setting of human stress research. Thermal imprints were compared to established stress markers (heart rate, heart rate variability, finger temperature, alpha-amylase and cortisol) in 15 participants undergoing anticipation, stress and recovery phases of two laboratory stress tests, the Cold Pressor Test and the Trier Social Stress Test. The majority of the thermal imprints proved to be change-sensitive in both tests. While correlations between the thermal imprints and established stress markers were mostly non-significant, the thermal imprints (but not the established stress makers) did correlate with stress-induced mood changes. Multivariate pattern analysis revealed that in contrast to the established stress markers the thermal imprints could not disambiguate anticipation, stress and recovery phases of both tests. Overall, these results suggest that thermal infrared imaging is a valuable method for the estimation of sympathetic activity in the stress laboratory setting. The use of this non-invasive method may be particularly beneficial for covert recordings, in the study of special populations showing difficulties in complying with the standard instruments of data collection and in the domain of psychophysiological covariance research. Meanwhile, the established stress markers seem to be superior when it comes to the characterization of complex physiological states during the different phases of the stress cycle.
Concepts originating from ancient Eastern texts are now being explored scientifically, leading to new insights into mind/brain function. Meditative practice, often viewed as an emotion regulation strategy, has been associated with pain reduction, low pain sensitivity, chronic pain improvement, and thickness of pain-related cortices. Zen meditation is unlike previously studied emotion regulation techniques; more akin to ‘no appraisal’ than ‘reappraisal’. This implies the cognitive evaluation of pain may be involved in the pain-related effects observed in meditators. Using functional magnetic resonance imaging and a thermal pain paradigm we show that practitioners of Zen, compared to controls, reduce activity in executive, evaluative and emotion areas during pain (prefrontal cortex, amygdala, hippocampus). Meditators with the most experience showed the largest activation reductions. Simultaneously, meditators more robustly activated primary pain processing regions (anterior cingulate cortex, thalamus, insula). Importantly, the lower pain sensitivity in meditators was strongly predicted by reductions in functional connectivity between executive and pain-related cortices. Results suggest a functional decoupling of the cognitive-evaluative and sensory-discriminative dimensions of pain, possibly allowing practitioners to view painful stimuli more neutrally. The activation pattern is remarkably consistent with the mindset described in Zen and the notion of mindfulness. Our findings contrast and challenge current concepts of pain and emotion regulation and cognitive control; commonly thought to manifest through increased activation of frontal executive areas. We suggest it is possible to self-regulate in a more ‘passive’ manner, by reducing higher-order evaluative processes, as demonstrated here by the disengagement of anterior brain systems in meditators.