Decrease in nasal temperature of rhesus monkeys (Macaca mulatta) in negative emotional state

Oral administration of ethinyl estradiol and the brain-selective estrogen prodrug DHED in a female common marmoset model of menopause: Effects on cognition, thermoregulation, and sleep

Menopausal symptoms of sleep disturbances, cognitive deficits, and hot flashes are understudied, in part due to the lack of animal models in which they co-occur. Common marmosets (Callithrix jacchus) are valuable nonhuman primates for studying these symptoms, and we examined changes in cognition (reversal learning), sleep (48 h/wk of sleep recorded by telemetry), and thermoregulation (nose temperature in response to mild external warming) in middle-aged, surgically-induced menopausal marmosets studied at baseline, during 3-week phases of ethinyl estradiol (EE2, 4 μg/kg/day, p.o.) treatment and after EE2 withdrawal. We also assessed a brain-selective hormonal therapy devoid of estrogenic effects in peripheral tissues on the same measures (cognition, sleep, thermoregulation) after treatment with the estrogen prodrug 10β,17β-dihydroxyestra-1,4-dien-3-one (DHED, 100 μg/kg/day, p.o) and DHED withdrawal. Reversal learning performance was improved with EE2 or DHED treatment relative to phases without hormone administration, as indicated by a faster reversal of the stimulus/reward contingencies. Both EE2 and DHED increased non-REM sleep and reduced nighttime awakenings relative to baseline, but to the detriment of REM sleep which was highest at baseline. Nasal temperature in response to mild external warming was highest, and overnight core body temperature lowest, in the DHED treatment phase compared to both the EE2 and baseline phases. These results suggest that low dose estradiol, delivered either peripherally or centrally via DHED, benefits selective aspects of cognition and sleep in a marmoset menopause model. DHED appears a promising therapeutic candidate for alleviating the cognitive and sleep disruptions associated with estrogen deficiency in primates.

Pasture access and eye temperature in dairy cows

Pasture access can benefit dairy cows' behavior, health, and welfare, but herds are increasingly housed indoors full-time. Recent infrared thermal-imaging (thermography) studies suggest that higher eye temperatures may be a physiological indicator of chronic stress. We, therefore, hypothesized that, compared to cows with pasture access, cows housed indoors full-time would have higher eye temperatures. In a two-phase crossover experiment, 29 Holstein-Friesian dairy cows experienced 18 days of overnight pasture access and 18 days of full-time indoor housing. We measured each animal's eye temperature 16 times (eight/phase). During Phase One, cows with pasture access had higher eye temperatures than cows housed indoors full-time (contrary to our hypothesis). However, during Phase Two, cows with pasture access had lower eye temperatures than cows housed indoors full-time. It is, therefore, unclear whether eye temperature reflected disparities in dairy cow welfare between different housing treatments.

Your blush gives you away: detecting hidden mental states with remote photoplethysmography and thermal imaging

Multimodal emotion recognition techniques are increasingly essential for assessing mental states. Image-based methods, however, tend to focus predominantly on overt visual cues and often overlook subtler mental state changes. Psychophysiological research has demonstrated that heart rate (HR) and skin temperature are effective in detecting autonomic nervous system (ANS) activities, thereby revealing these subtle changes. However, traditional HR tools are generally more costly and less portable, while skin temperature analysis usually necessitates extensive manual processing. Advances in remote photoplethysmography (r-PPG) and automatic thermal region of interest (ROI) detection algorithms have been developed to address these issues, yet their accuracy in practical applications remains limited. This study aims to bridge this gap by integrating r-PPG with thermal imaging to enhance prediction performance. Ninety participants completed a 20-min questionnaire to induce cognitive stress, followed by watching a film aimed at eliciting moral elevation. The results demonstrate that the combination of r-PPG and thermal imaging effectively detects emotional shifts. Using r-PPG alone, the prediction accuracy was 77% for cognitive stress and 61% for moral elevation, as determined by a support vector machine (SVM). Thermal imaging alone achieved 79% accuracy for cognitive stress and 78% for moral elevation, utilizing a random forest (RF) algorithm. An early fusion strategy of these modalities significantly improved accuracies, achieving 87% for cognitive stress and 83% for moral elevation using RF. Further analysis, which utilized statistical metrics and explainable machine learning methods including SHapley Additive exPlanations (SHAP), highlighted key features and clarified the relationship between cardiac responses and facial temperature variations. Notably, it was observed that cardiovascular features derived from r-PPG models had a more pronounced influence in data fusion, despite thermal imaging's higher predictive accuracy in unimodal analysis.

Use of infrared thermography to detect reactions to stressful events: does animal personality matter?

The study of the relationship between animal stress and personality for free-ranging animals is limited and provides contrasting results. The perception of stressors by an individual may vary due to its personality, and certain personality traits may help individuals to better cope with them. Using non-invasive infrared thermography (IRT), we investigated the link between physiological and behavioral components expressed during an acute stress event by free-ranging Fremont's squirrels (Tamiasciurus fremonti). We expected that, during the acute stress event of being approached by the researcher, individuals that showed a fast pace-of-life syndrome (bolder, more active, and less social/more aggressive) based on an arena test would exhibit stronger sympathetic-adrenal-medullary system reactivity showing a more intense stress-induced hyperthermia (high core body temperature and low peripheral temperature) than individuals with a slow pace of life (shy, less active, and more social). We successfully employed IRT technology to images of Fremont's squirrels with identification of the individuals' body parts (eye, nose, ear, hind foot). However, we found no support for our hypothesis. Squirrels' body surface temperatures told us more about a squirrel's external environment and less about the thermal state of the body in that environment following a stressful event. Further studies need to assess how to make IRT effective and efficient in the field and improve its performance in studying the relationships between physiology and personality in wildlife.

Behavioral, physiological, and genetic drivers of coping in a non-human primate

Animals experience stressful situations, from predation to social conflicts, but mostly deal with them successfully. This adaptive mechanism, coping, reduces the adverse effects of stressors, and its failure may result in reduced fitness. Substantial inter-individual variation in coping is observed, yet little is known about how behavioral, physiological and genetic drivers regulate coping holistically and contribute to such variations. We assessed behavioral coping styles (n=30), emotional arousal (n=12), and personalities (n=32) of long-tailed macaques (Macaca fascicularis) and also investigated the association of coping with a valine/methionine polymorphism encoded by a critical human stress regulatory gene, catechol-O-methyltransferase (COMT) (n=26). Personality and the human equivalent COMT Val/Met polymorphism were associated with "nonaggression-based" and "aggression-based" coping styles. Compared to nonaggression-based, aggression-based copers maintained higher average facial temperatures, indicating potentially lower emotional arousal, as measured using infrared thermography. These findings demonstrate a complex interplay of various proximate mechanisms governing coping in a non-human primate.

Evaluation of Non-Contact Device to Measure Body Temperature in Sheep

Non-contact devices have been used in the measurement of body temperature in livestock production as a tool for testing disease in different species. However, there are few studies about the variation and correlations in body temperature between rectal temperature (RT) and non-contact devices such as non-contact infrared thermometers (NCIT) and thermal imaging/infrared thermography (IRT). The objective of this work was to evaluate the accuracy of non-contact devices to measure the body temperature in sheep, considering six body regions and the possibility of implementing these systems in herd management. The experiment was carried out at the experimental farm of the Catholic University of Valencia, located in the municipality of Massanassa in July of 2021, with 72 dry manchega ewes, and we compared the rectal temperature with two types of non-contact infrared devices for the assessment of body temperature in healthy sheep. Except for the temperature taken by NCIT at the muzzle, the correlation between RT vs. NCIT or IRT showed a low significance or was difficult to use for practical flock management purposes. In addition, the variability between devices was high, which implies that measurements should be interpreted with caution in warm climates and open pens, such as most sheep farms in the Spanish Mediterranean area. The use of infrared cameras devices to assess body temperature may have a promising future, but in order to be widely applied as a routine management method on farms, the system needs to become cheaper, simpler in terms of measurements and quicker in terms of analyzing results.

Non-invasive, real-time stress measurement: Vocalization compared with thermal imaging in kittens of the domestic cat in response to social separation

Finding tools to assess the stress response which can be easily applied, are non-invasive, reliable and measured in real time is still a relevant topic in many areas of biology. Vocal characteristics and temperature of certain body areas have been suggested to reflect HPA axis and ANS activation. We hypothesized that changes in vocalizations and peripheral body temperature will show the magnitude of the stress response, and that the change in these will covary. Our aim was to measure the change in vocal characteristics and eye and nasal temperature of kittens (n = 43 from nine litters of seven mixed-breed mothers) during a potentially stressful event and to test how these correlated. We found change in several vocal and thermal parameters during a short social separation. Our findings indicate that arousal due to ANS activation in kittens of the domestic cat resulted in an increasing number of vocalisations of longer duration and higher intensity, and in lower and a wider range in fundamental frequency. Calls also became less tonal with more jitter. Change in temperature was generally negative in the lacrimal caruncle as well as in the rhinarium, but with great variance across individuals. Change in eye temperature positively correlated with the intensity of the calls and the change in nose temperature positively correlated with the change in call length. The results suggest the continued difficulty in interpreting both physiological and behavioural data to assess an individual´s stress response.

It's cool to be stressed: body surface temperatures track sympathetic nervous system activation during acute stress

The acute stress response can be considered the primary evolutionary adaptation to maximise fitness in the face of unpredictable environmental challenges. However, the difficulties of assessing physiology in natural environments mean that comparatively little is known about how response variation influences fitness in free-living animals. Currently, determining acute stress physiology typically involves blood sampling or cardiac monitoring. Both require trapping and handling, interrupting natural behaviour, and potentially biasing our understanding toward trappable species/individuals. Importantly, limits on repeated sampling also restrict response phenotype characterisation, vital for linking stress with fitness. Surface temperature dynamics resulting from peripheral vasomotor activity during acute stress are increasingly promoted as alternative physiological stress indicators, which can be measured non-invasively using infrared thermal imaging, overcoming many limitations of current methods. Nonetheless, which aspects of stress physiology they represent remains unclear, as the underlying mechanisms are unknown. To date, validations have primarily targeted the hypothalamic-pituitary-adrenal axis, when the sympathetic-adrenal-medullary (SAM) system is likely the primary driver of vasomotor activity during acute stress. To address this deficit, we compared eye and bill region surface temperatures (measured using thermal imaging) with SAM system activity (measured as heart rate variability via electrocardiogram telemetry) in wild-caught captive house sparrows (Passer domesticus) during capture and handling. We found that lower body surface temperatures were associated with increased sympathetic nervous system activation. Consequently, our data confirm that body surface temperatures can act as a proxy for sympathetic activation during acute stress, providing potentially transformative opportunities for linking the acute stress response with fitness in the wild.

Non-invasive assessment of positive affective state using infra-red thermography in rats

With recent increased focus on positive welfare in animal welfare science, there is demand for objective positive welfare indicators. It is unclear whether changes in body surface temperature can be used to non-invasively identify and quantify positive states in mammals. We recorded continuous measurements of tail surface temperature using infra-red thermography (IRT) and concurrent behavioural observations in male and female Wistar rats (Rattus norvegicus). If tail surface temperature can differentiate between positive and negative experiences, we expect a qualitatively different response compared to negative experiences. Three groups of rats were presented with increasing magnitudes of food rewards (neutral/none, one and three rewards). The rats were placed in an arena to which they were habituated and filmed for 30 s before and 30 min after exposure to different rewards. Tail temperature initially decreased from the pre-reward baseline and subsequently returned towards baseline temperature. The overall pattern of the change was the same as for rats subjected to negative stimuli in previous studies. Nevertheless, dynamic changes in tail temperature, specifically the rate of recovery and the behavioural response (exploration), differed between neutral and rewarded rats but failed to distinguish reward magnitude. Sex differences were found in both thermal and behavioural responses, unrelated to reward magnitudes. Female rats exhibited a greater initial response with a slower recovery than male rats, emphasising the value of using of both sexes in animal welfare research. This study improves our understanding of the effects of positive emotions induced by food reward on peripheral body temperature and behaviour.

Body surface temperature of rats reveals both magnitude and sex differences in the acute stress response

Understanding how biological markers of stress relate to stressor magnitude is much needed and can be used in welfare assessment. Changes in body surface temperature can be measured using infrared thermography (IRT) as a marker of a physiological response to acute stress. While an avian study has shown that changes in body surface temperature can reflect the intensity of acute stress, little is known about surface temperature responses to stressors of different magnitudes and its sex-specificity in mammals, and how they correlate with hormonal and behavioural responses. We used IRT to collect continuous surface temperature measurements of tail and eye of adult male and female rats (Rattus norvegicus), for 30 minutes after exposure to one of three stressors (small cage, encircling handling or rodent restraint cone) for one minute, and cross-validated the thermal response with plasma corticosterone (CORT) and behavioural assessment. To obtain individual baseline temperatures and thermal responses to stress, rats were imaged in a test arena (to which they were habituated) for 30 seconds before and 30 minutes after being exposed to the stressor. In response to the three stressors, tail temperature initially decreased and then recovered to, or overshot the baseline temperature. Tail temperature dynamics differed between stressors; being restrained in the small cage was associated with the smallest drop in temperature, in male rats, and the fastest thermal recovery, in both sexes. Increases in eye temperature only distinguished between stressors early in the response and only in females. The post stressor increase in eye temperature was greater in the right eye of males and the left eye of females. In both sexes encircling may have been associated with the fastest increase in CORT. These results were in line with observed behavioural changes, with greater movement in rats exposed to the small cage and higher immobility after encircling. The female tail and eye temperature, as well as the CORT concentrations did not return to pre-stressor levels in the observation period, in conjunction with the greater occurrence of escape-related behaviours in female rats. These results suggest that female rats are more vulnerable to acute restraint stress compared to male rats and emphasise the importance of using both sexes in future investigations of stressor magnitude. This study demonstrates that acute stress induced changes in mammalian surface temperature measured with IRT relate to the magnitude of restraint stress, indicate sex differences and correlate with hormonal and behavioural responses. Thus, IRT has the potential to become a non-invasive method of continuous welfare assessment in unrestrained mammals.

Effect of packing (load carrying) on body temperatures and their circadian rhythms in donkeys (Equus asinus) during the hot-dry season

The study aimed to evaluate the effects of packing (load carrying) on rectal and body surface temperatures and their circadian rhythmicity in donkeys during the hot-dry season. Twenty pack donkeys of both sexes (15 males and 5 non-pregnant females), aged 2-3 years, with average weight of 93 ± 2.7 kg and divided into two groups randomly, served as experimental subjects. Group 1 donkeys (packing + trekking) were subjected to packing in addition to trekking, while group 2 (trekking only) did not carry any load. All the donkeys were trekked, covering a distance of 20 km. The procedure was repeated three times within the week, one day apart. During the experiment, dry-bulb temperature (DBT), relative humidity (RH) and temperature-humidity index (THI), wind speed and topsoil temperature were recorded; and rectal temperature (RT) and body surface temperature (BST) were measured before and immediately after packing. Starting from 16 h after the last packing, circadian rhythms of RT and BST were recorded at 3-h intervals for 27-h period. The RT and BST were measured by digital thermometer and non-contact infrared thermometer, respectively. The DBT and RH, especially after packing (35.83 ± 0.2 °C and 20.00 ± 0.0%, respectively), were outside the thermoneutral zone for donkeys. The RT value (38.63 ± 0.1 °C) in packing + trekking donkeys recorded immediately (15 min) after packing was higher (P < 0.05) than the value obtained in trekking only donkeys (37.27 ± 0.1 °C). The overall mean RT recorded during the continuous 27-h period of measurement, starting from 16 h after the last packing procedure was higher (P < 0.05) in packing + trekking donkeys (36.93 ± 0.2 °C) compared with trekking only donkeys (36.29 ± 0.3 °C). The BSTs recorded in both groups were higher (P < 0.05) immediately after packing when compared with pre-packing values, but insignificant 16-h post-packing. The RT and BST values were generally higher in the photophase and lower during the scotophase in both groups of donkeys during the continuous recordings. The eye temperature was the closest to the RT, followed by scapular temperature, while the coronary band temperature was the farthest. The mesor of RT in packing + trekking donkeys (37.06 ± 0.2 °C) was significantly higher than in donkeys that were trekked only (36.46 ± 0.1 °C). The amplitude of RT in trekking only donkeys (1.20 ± 0.1 °C) was wider (P < 0.05) than that obtained in packing + trekking donkeys (0.80 ± 0.1 °C). The acrophase and bathyphase occurred later in packing + trekking donkeys (18:10 ± 0.3 h and 6:10 ± 0.3 h, respectively), compared to the trekking only donkeys (16:50 ± 0.2 h and 4:50 ± 0.2 h, respectively). In conclusion, exposure to thermally stressful prevailing environmental conditions during packing increased the body temperature responses, especially in packing + trekking donkeys. Packing significantly influenced the circadian rhythms of body temperatures in working donkeys, as evidenced by differences in circadian rhythm parameters in packing + trekking group, compared with trekking only donkeys during the hot-dry season.

Thermal Imaging to Assess the Health Status in Wildlife Animals under Human Care: Limitations and Perspectives

Promoting animal welfare in wildlife species under human care requires the implementation of techniques for continuously monitoring their health. Infrared thermography is a non-invasive tool that uses the radiation emitted from the skin of animals to assess their thermal state. However, there are no established thermal windows in wildlife species because factors such as the thickness or color of the skin, type/length of coat, or presence of fur can influence the readings taken to obtain objective, sensitive values. Therefore, this review aims to discuss the usefulness and application of the ocular, nasal, thoracic, abdominal, and podal anatomical regions as thermal windows for evaluating zoo animals' thermal response and health status. A literature search of the Web of Science, Science Direct, and PubMed databases was performed to identify relevant studies that used IRT with wild species as a complementary diagnostic tool. Implementing IRT in zoos or conservation centers could also serve as a method for determining and monitoring optimal habitat designs to meet the needs of specific animals. In addition, we analyze the limitations of using IRT with various wildlife species under human care to understand better the differences among animals and the factors that must be considered when using infrared thermography.

Thermal imaging reveals social monitoring during social feeding in wild chimpanzees

Understanding the affective lives of animals has been a long-standing challenge in science. Recent technological progress in infrared thermal imaging has enabled researchers to monitor animals' physiological states in real-time when exposed to ecologically relevant situations, such as feeding in the company of others. During social feeding, an individual's physiological states are likely to vary with the nature of the resource and perceptions of competition. Previous findings in chimpanzees have indicated that events perceived as competitive cause decreases in nasal temperatures, whereas the opposite was observed for cooperative interactions. Here, we tested how food resources and audience structure impacted on how social feeding events were perceived by wild chimpanzees. Overall, we found that nasal temperatures were lower when meat was consumed as compared to figs, consistent with the idea that social feeding on more contested resources is perceived as more dangerous and stressful. Nasal temperatures were significant affected by interactions between food type and audience composition, in particular the number of males, their dominance status, and their social bond status relative to the subject, while no effects for the presence of females were observed. Our findings suggest that male chimpanzees closely monitor and assess their social environment during competitive situations, and that infrared imaging provides an important complement to access psychological processes beyond observable social behaviours. This article is part of the theme issue 'Cognition, communication and social bonds in primates'.

My Fear Is Not, and Never Will Be, Your Fear: On Emotions and Feelings in Animals

Do nonhuman animals (henceforth, animals) have emotions, and if so, are these similar to ours? This opinion piece aims to add to the recent debate about this question and provides a critical re-evaluation of what can be concluded about animal and human emotions. Emotions, and their cognitive interpretation, i.e., feelings, serve important survival functions. Emotions, we believe, can exist without feelings and are unconsciously influencing our behavior more than we think, and possibly more so than feelings do. Given that emotions are expressed in body and brain, they can be inferred from these measures. We view feelings primarily as private states, which may be similar across closely related species but remain mostly inaccessible to science. Still, combining data acquired through behavioral observation with data obtained from noninvasive techniques (e.g., eyetracking, thermography, hormonal samples) and from cognitive tasks (e.g., decision-making paradigms, cognitive bias, attentional bias) provides new information about the inner states of animals, and possibly about their feelings as well. Given that many other species show behavioral, neurophysiological, hormonal, and cognitive responses to valenced stimuli equivalent to human responses, it seems logical to speak of animal emotions and sometimes even of animal feelings. At the very least, the contemporary multi-method approach allows us to get closer than ever before. We conclude with recommendations on how the field should move forward.

Facial temperature and pupil size as indicators of internal state in primates

Studies in human subjects have revealed that autonomic responses provide objective and biologically relevant information about cognitive and affective states. Measures of autonomic responses can also be applied to studies of non-human primates, which are neuro-anatomically and physically similar to humans. Facial temperature and pupil size are measured remotely and can be applied to physiological experiments in primates, preferably in a head-fixed condition. However, detailed guidelines for the use of these measures in non-human primates is lacking. Here, we review the neuronal circuits and methodological considerations necessary for measuring and analyzing facial temperature and pupil size in non-human primates. Previous studies have shown that the modulation of these measures primarily reflects sympathetic reactions to cognitive and emotional processes, including alertness, attention, and mental effort, over different time scales. Integrated analyses of autonomic, behavioral, and neurophysiological data in primates are promising methods that reflect multiple dimensions of emotion and could potentially provide tools for understanding the mechanisms underlying neuropsychiatric disorders and vulnerabilities characterized by cognitive and affective disturbances.

An evaluation of thermal imaging as a welfare monitoring tool for captive chimpanzees

Among the growing list of novel tools with which to assess animal welfare is the use of thermal (infrared) imaging. The technology has already been utilized to identify emotional arousal in several nonhuman primate species, though most of these approaches have necessitated the use of relatively controlled settings. Here, we were interested to determine the feasibility of such techniques in a sanctuary setting in which chimpanzees were unrestrained and able to move freely around their enclosures. Furthermore, we sought to evaluate how such thermal images could be paired with corresponding long-term behavioral data and contribute to a multifactorial welfare monitoring system. Over a 6-month period, we simultaneously collected both behavioral and thermographic data on 29 chimpanzees living in four social groups. While we took a thermal image with every behavioral data point, we found that only a small proportion (6.38%) of the thermal images we captured were of sufficient quality to analyze. Most of these usable thermal images (55%) corresponded with a behavioral observation scored as "inactive," and thus other, less frequent behaviors are not so well represented in our final data set. From our data set, we were able to determine that nasal temperatures were relatively lower when chimpanzees were categorized in active behaviors compared to inactive behaviors, providing some validity measures to our approach. While there are other potential applications for thermal imaging in the behavioral management of chimpanzees, managers should consider the practical limitations of developing long-term welfare monitoring programs that rely on thermographic data.

Infrared Thermography in the Study of Animals' Emotional Responses: A Critical Review

Simple Summary

Assessing animal welfare has proven to be a challenging task with important consequences for their management. In the last few years, infrared thermography has gained increasing scientific consensus as a method to analyze emotional reactions to different stimuli in different taxa. This review aims to explore particularly the use of infrared thermography in the assessment of animals’ emotions, mainly focusing on pets, laboratory, and husbandry animals. If properly used, this technique has proven to be a noninvasive, reliable method to identify emotional activations.

Abstract

Whether animals have emotions was historically a long-lasting question but, today, nobody disputes that they do. However, how to assess them and how to guarantee animals their welfare have become important research topics in the last 20 years. Infrared thermography (IRT) is a method to record the electromagnetic radiation emitted by bodies. It can indirectly assess sympathetic and parasympathetic activity via the modification of temperature of different body areas, caused by different phenomena such as stress-induced hyperthermia or variation in blood flow. Compared to other emotional activation assessment methods, IRT has the advantage of being noninvasive, allowing use without the risk of influencing animals’ behavior or physiological responses. This review describes general principles of IRT functioning, as well as its applications in studies regarding emotional reactions of domestic animals, with a brief section dedicated to the experiments on wildlife; it analyzes potentialities and possible flaws, confronting the results obtained in different taxa, and discusses further opportunities for IRT in studies about animal emotions.

The Rapid Rise of Next-Generation Natural History

Many ecologists have lamented the demise of natural history and have attributed this decline to a misguided view that natural history is outdated and unscientific. Although there is a perception that the focus in ecology and conservation have shifted away from descriptive natural history research and training toward hypothetico-deductive research, we argue that natural history has entered a new phase that we call “next-generation natural history.” This renaissance of natural history is characterized by technological and statistical advances that aid in collecting detailed observations systematically over broad spatial and temporal extents. The technological advances that have increased exponentially in the last decade include electronic sensors such as camera-traps and acoustic recorders, aircraft- and satellite-based remote sensing, animal-borne biologgers, genetics and genomics methods, and community science programs. Advances in statistics and computation have aided in analyzing a growing quantity of observations to reveal patterns in nature. These robust next-generation natural history datasets have transformed the anecdotal perception of natural history observations into systematically collected observations that collectively constitute the foundation for hypothetico-deductive research and can be leveraged and applied to conservation and management. These advances are encouraging scientists to conduct and embrace detailed descriptions of nature that remain a critically important component of the scientific endeavor. Finally, these next-generation natural history observations are engaging scientists and non-scientists alike with new documentations of the wonders of nature. Thus, we celebrate next-generation natural history for encouraging people to experience nature directly.

Influence of Stress Assessed through Infrared Thermography and Environmental Parameters on the Performance of Fattening Rabbits

Simple Summary

The aim of this study was to evaluate the impact of stress due to heat (temperature-humidity index; THI) or handling (human restraining), assessed using infrared thermography, on the performance parameters of rabbits of a Spanish Common breed. Thirty-nine rabbits weaned at the age of 28 days were analyzed during a 38-d fattening period at two times of the year: a cold period and a warm period. The rabbits’ stress due to handling was assessed by the temperature difference taken by infrared thermography in the inner ear of the animals, before and after being handled. In general, the productive results were low, since it was an unimproved rustic breed. The animals were more productive in the cold season as the values obtained for daily feed intake (DFI), average daily gain (ADG), total body weight (TBW), total feed intake (TFI) and total weight gain (TWG) were higher then, while the feed conversion ratio (FCR) was higher in the warm season. The greater the stress due to handling, the less efficient the animals were. It was therefore concluded that changes in animal welfare caused by the rabbits’ reactivity to both climatic and individual factors affect animal productivity.

Abstract

Rabbits often experience stress when they perceive certain stimuli, such as handling. The physiological response of animals to stress and temperament is associated with feeding efficiency, with those with the least capacity to react to stress showing the highest performance. The aim of this study was to evaluate the impact of stress due to heat (temperature-humidity index; THI) or handling, assessed using infrared thermography, on the performance parameters of rabbits of a Spanish Common breed. Thirty-nine rabbits were analyzed during a 38-d fattening period at two times of the year: a cold period and a warm period. The rabbits’ stress due to handling was assessed by the temperature difference taken in the inner ear, before and after being handled. The animals were more productive in the cold season. Temperature-humidity index significantly influenced average daily gain (ADG) and daily feed intake (DFI). Rabbits with higher levels of stress showed higher ADG, DFI and feed conversion ratio (FCR) values. The greater the stress due to handling, the less efficient the animals were. FCR increased with higher THI. It was concluded that changes in animal welfare caused by the rabbits’ reactivity to both climatic and individual factors affect animal productivity.

Under the skin: Exploring 2-month-olds' thermal reactions in different social interactions with mother and stranger

Physiological adaptations to external stressors can reveal socio-cognitive health in infancy. With the use of thermal imaging and behavioural analyses, the current study examined the arousal markers accompanying infants' interactions with a familiar and an unfamiliar person. To address the current research question, the mother and a complete stranger interacted with 2 to 3 month-old infants (N= 10, 2 boys)in three different conditions: Neutral, Play, and Compliment. Behavioral analyses showed that overall gaze was longer to the Stranger compared to the Mother independent of condition. Physiological findings showed that skin temperature was significantly higher with the stranger independent of condition. The regions of the face that passed the significance threshold included the maxillary area, the nose, and the forehead. Both behavioral and physiological findings emphasize the ability of the infant to distinguish between a familiar and an unfamiliar person. Most importantly, however thermal imaging has proven to be a promising tool in physiologically differentiating between variable social conditions in very young infants opening up a new experimental portal for identifying healthy physiological development.

Do marmosets understand others' conversations? A thermography approach

What information animals derive from eavesdropping on interactions between conspecifics, and whether they assign value to it, is difficult to assess because overt behavioral reactions are often lacking. An inside perspective of how observers perceive and process such interactions is thus paramount. Here, we investigate what happens in the mind of marmoset monkeys when they hear playbacks of positive or negative third-party vocal interactions, by combining thermography to assess physiological reactions and behavioral preference measures. The physiological reactions show that playbacks were perceived and processed holistically as interactions rather than as the sum of the separate elements. Subsequently, the animals preferred those individuals who had been simulated to engage in positive, cooperative vocal interactions during the playbacks. By using thermography to disentangle the mechanics of marmoset sociality, we thus find that marmosets eavesdrop on and socially evaluate vocal exchanges and use this information to distinguish between cooperative and noncooperative conspecifics.

Emotion recognition in nonhuman primates: How experimental research can contribute to a better understanding of underlying mechanisms

Recognising conspecifics' emotional expressions is important for nonhuman primates to navigate their physical and social environment. We address two possible mechanisms underlying emotion recognition: emotional contagion, the automatic matching of the observer's emotions to the emotional state of the observed individual, and cognitive empathy, the ability to understand the meaning and cause of emotional expressions while maintaining a distinction between own and others' emotions. We review experimental research in nonhuman primates to gain insight into the evolution of emotion recognition. Importantly, we focus on how emotional contagion and cognitive empathy can be studied experimentally. Evidence for aspects of cognitive empathy in different nonhuman primate lineages suggests that a wider range of primates than commonly assumed can infer emotional meaning from emotional expressions. Possibly, analogous rather than homologous evolution underlies emotion recognition. However, conclusions regarding its exact evolutionary course require more research in different modalities and species.

Infrared thermography cannot be used to approximate core body temperature in wild primates

Understanding the physiological processes that underpin primate performance is key if we are to assess how a primate might respond when navigating new and changing environments. Given the connection between a mammal's ability to thermoregulate and the changing demands of its thermal environment, increasing attention is being devoted to the study of thermoregulatory processes as a means to assess primate performance. Infrared thermography can be used to record the body surface temperatures of free-ranging animals. However, some uncertainty remains as to how these measurements can be used to approximate core body temperature. Here, we use data collected from wild vervet monkeys (Chlorocebus pygerythrus) to examine the relationship between infrared body surface temperature, core body (intra-abdominal) temperature, and local climate, to determine to what extent surface temperatures reflect core body temperature. While we report a positive association between surface and core body temperature-a finding that has previously been used to justify the use of surface temperature measurements as a proxy for core temperature regulation-when we controlled for the effect of the local climate in our analyses, this relationship was no longer observed. That is, body surface temperatures were solely predicted by local climate, and not core body temperatures, suggesting that surface temperatures tell us more about the environment a primate is in, and less about the thermal status of its body core in that environment. Despite the advantages of a noninvasive means to detect and record animal temperatures, infrared thermography alone cannot be used to approximate core body temperature in wild primates.

Where Do We Stand in the Domestic Dog ( Canis familiaris ) Positive-Emotion Assessment: A State-of-the-Art Review and Future Directions

Although there have been a growing number of studies focusing on dog welfare, the research field concerning dog positive-emotion assessment remains mostly unexplored. This paper aims to provide a state-of-the-art review and summary of the scattered and disperse research on dog positive-emotion assessment. The review notably details the current advancement in dog positive-emotion research, what approaches, measures, methods, and techniques have been implemented so far in emotion perception, processing, and response assessment. Moreover, we propose possible future research directions for short-term emotion as well as longer-term emotional states assessment in dogs. The review ends by identifying and addressing some methodological limitations and by pointing out further methodological research needs.

Does Osteopathic Manipulative Treatment Induce Autonomic Changes in Healthy Participants? A Thermal Imaging Study

Osteopathic manipulative treatment (OMT) has been demonstrated to be an effective therapy in several clinical conditions and age groups. Despite the clinical effectiveness, lack of robust data in terms of neurobiological, specifically autonomic, mechanisms of action is observed. Preliminary studies showed a parasympathetic effect leading to a trophotropic effect of OMT. However, these data are limited to heart rate variability (HRV) analysis. In order to study further the role of OMT on the autonomic nervous system, a cross-over randomized controlled trial RCT has been designed to test the effect of osteopathic treatment compared to sham therapy on a range of autonomic parameters. Thermal images, HRV and skin conductance data were collected on a sample of healthy adults. The study design consisted of two sessions (OMT and SHAM), 1 treatment per week, lasting 35 min each, composed of 5 min of baseline, 25 min of treatment, and 5 min of post-touch. During the baseline and the post-treatment, participants received no touch. Thirty-seven participants (aged 27 ± 5 years old, male ratio 40%) completed the study. Multivariate analysis showed a significant parasympathetic effect of group as well as of epoch on thermographic data of the nose (estimate 0.38; 95% CI 0.12–0.63; p < 0.01), left (0.17; 0.06–0.27; <0.001) and right (0.16; 0.07–0.24; <0.001) perioral as well as on the forehead (0.07; 0.01–0.12; <0.01) regions but not for the chin (0.08; −0.02 to 0.18; 0.13). Consistent with a parasympathetic effect, analyses demonstrated a difference between OMT and sham groups on the nuHF (p < 0.001) and DFA-a1 (p < 0.01) as well as on skin conductance (<0.01). The present research supports the hypothesis that a single session of OMT as compared to sham induces autonomic consequences in healthy non-symptomatic adults. Clinicaltrial.gov identifier: NCT03888456, https://clinicaltrials.gov/ct2/show/NCT03888456.

Evaluation of infrared thermography as a non-invasive method of measuring the autonomic nervous response in sheep

Eye temperature measured using infrared thermography (IRT) can be used as a non-invasive measure of autonomic nervous system (ANS) activity in cattle. The objective of this study was to evaluate if changes in eye temperature (measured using IRT) can be used to non-invasively measure ANS activity in sheep. Twenty, 2 to 4-year-old, Romney ewes were randomly assigned to receive either epinephrine (EPI) or physiological saline (SAL) for 5 min administered via jugular catheter (n = 10 ewes/treatment). Eye temperature (°C) was recorded continuously using IRT for approximately 25 min before and 20 min after the start of infusion. Heart rate and heart rate variability, measured using the root mean square of successive differences (RMSSD) and the standard deviation of all inter-beat intervals (SDNN), were recorded for 5 min before and up to 10 min after the start of infusion. Blood samples were taken before and after the infusion period to measure plasma epinephrine, norepinephrine, cortisol and packed cell volume (PCV) concentrations. During the infusion period, maximum eye temperature was on average higher (P<0.05) in sheep that received epinephrine than those that received saline. On average, heart rate was higher (SAL: 87.5 beats/min, EPI: 123.2 beats/min, SED = 7.07 beats/min; P<0.05), and RMSSD (SAL: 55.3 ms, EPI: 17.3 ms, SED = 14.18 ms) and SDNN (SAL: 54.3 ms, EPI: 21.5 ms, SED = 10.00 ms) lower (P<0.05) in ewes during the 5 min post-infusion period compared with ewes that received saline. An infusion of epinephrine resulted in higher geometric mean epinephrine (P<0.05) and cortisol (P<0.05) but not norepinephrine (P>0.05) concentrations in ewes compared to an infusion of saline. PCV concentrations were higher (P<0.001) by 7 ± 1.0% (mean±SED) in ewes after an epinephrine infusion. These results suggest that heart rate variability is a sensitive, non-invasive method that can be used to measure ANS activity in sheep, whereas change in eye temperature measured using IRT is a less sensitive method.

Challenges in the comparative study of empathy and related phenomena in animals

The aim of this review is to discuss recent arguments and findings in the comparative study of empathy. Based on a multidisciplinary approach including psychology and ethology, we review the non-human animal literature concerning theoretical frameworks, methodology, and research outcomes. One specific objective is to highlight discrepancies between theory and empirical findings, and to discuss ambiguities present in current data and their interpretation. In particular, we focus on emotional contagion and its experimental investigation, and on consolation and targeted helping as measures for sympathy. Additionally, we address the feasibility of comparing across species with behavioural data alone. One main conclusion of our review is that animal research on empathy still faces the challenge of closing the gap between theoretical concepts and empirical evidence. To advance our knowledge, we propose to focus more on the emotional basis of empathy, rather than on possibly ambiguous behavioural indicators, and we provide suggestions to overcome the limitations of previous research .

Communicative roots of complex sociality and cognition

Mammals living in more complex social groups typically have large brains for their body size and many researchers have proposed that the primary driver of the increase in brain size through primate and hominin evolution was the selection pressures associated with sociality. Many mammals, and especially primates, use flexible signals that show a high degree of voluntary control and these signals may play an important role in forming and maintaining social relationships between group members. However, the specific role that cognitive skills play in this complex communication, and how in turn this relates to sociality, is still unclear. The hypothesis for the communicative roots of complex sociality and cognition posits that cognitive demands behind the communication needed to form and maintain bonded social relationships in complex social settings drives the link between brain size and sociality. We review the evidence in support of this hypothesis and why key features of cognitively complex communication such as intentionality and referentiality should be more effective in forming and maintaining bonded relationships as compared with less cognitively complex communication. Exploring the link between cognition, communication and sociality provides insights into how increasing flexibility in communication can facilitate the emergence of social systems characterised by bonded social relationships, such as those found in non-human primates and humans. To move the field forward and carry out both within- and among-species comparisons, we advocate the use of social network analysis, which provides a novel way to describe and compare social structure. Using this approach can lead to a new, systematic way of examining social and communicative complexity across species, something that is lacking in current comparative studies of social structure.

Nasal skin temperature reveals changes in arousal levels due to time on task: An experimental thermal infrared imaging study

Infrared thermography, thanks to technological developments and lowering prices, is now getting considerable attention as a potential arousal monitor in the safety industry. Nasal skin temperature might be a valid index to track physiological variations due to reduced arousal levels, and its use could prevent a drowsiness-related deterioration of performance. However, the few studies that have investigated nasal skin temperature in applied settings have had inconsistent results. Here, we assessed the validity of nasal skin temperature to monitor changes in arousal levels (from alertness to drowsiness). The participants performed a 2-h simulated driving task while we simultaneously recorded their nasal skin temperature, brain activity (we used frontal delta electroencephalographic [EEG] activity as the reference index of alertness), and driving performance (speeding time). For those variables, we calculated growth curve models. We also collected subjective ratings of alertness and fatigue before and after the driving session. We found that the nasal skin temperature showed a cubic trajectory (it increased for the first 75 min, and then it began to decrease, but such deceleration gradually diminished over time). As expected, frontal delta EEG activity showed an inverted U-shaped quadratic trend (EEG power increased for the first hour and half, and gradually decreased during the last thirty minutes). The speeding time exhibited a similar pattern of change. Subjective sleepiness and fatigue increased after the task. Overall, our results suggest that nasal skin temperature seems to be a valid measure of arousal variations while performing a complex and dynamic everyday task.

The use of infrared thermography to investigate emotions in common marmosets

Measuring body surface temperature changes with infrared thermography has recently been put forward as a non-invasive alternative measure of physiological correlates of emotional reactions. In particular, the nasal region seems to be highly sensitive to emotional reactions. Several studies suggest that nasal temperature is negatively correlated with the level of arousal in humans and other primates, but some studies provide inconsistent results. Our goal was to establish the use of infrared thermography to quantify emotional reactions in common marmosets (Callithrix jacchus), with a focus on the nasal region. To do so we exposed 17 common marmosets to a set of positive, negative and control stimuli (positive: preferred food, playback of food calls; negative: playback of aggressive vocalizations, teasing; control: no stimulus). We compared nasal temperature before and after the stimuli and expected that highly aroused emotional states would lead to a drop in nasal temperature. To validate the thermography measure, we coded piloerection of the tail as an independent measure of arousal and expected a negative correlation between the two measures. Finally, we coded physical activity to exclude its potential confounding impact on nasal temperature. Our results show that all predictions were met: the animals showed a strong decrease in nasal temperature after the presentation of negative arousing stimuli (teasing, playback of aggressive vocalizations). Furthermore, these changes in nasal temperature were correlated with piloerection of the tail and could not be explained by changes in physical activity. In the positive and the control conditions, we found systematic sex differences: in males, the preferred food, the playbacks of food calls, as well as the control stimulus led to an increase in nasal temperature, whereas in females the temperature remained stable (preferred food, control) or decreased (playback of food calls). Based on naturalistic observations that document higher food motivation and competition among female marmosets, as well as stronger reactions to separation from group members in male marmosets, these sex differences corroborate a negative correlation between arousal and nasal temperature. Overall, our results support that measuring nasal temperature by infrared thermography is a promising method to quantify emotional arousal in common marmosets in a fully non-invasive and highly objective way.

Exploratory Investigation of Infrared Thermography for Measuring Gorilla Emotional Responses to Interactions with Familiar Humans

Simple Summary

Interactions between zoo professionals and animals, such as positive reinforcement training, occur regularly and are thought to be enriching for animals. However, there is little empirical information on how animals perceive these interactions or on the interactions’ effects on animals’ emotional states. Our objective was to assess the effectiveness of infrared thermography for measuring the emotional responses of three western lowland gorillas at the Detroit Zoo to routine interactions (positive reinforcement training and cognitive tasks) with familiar humans. In addition to thermal images, we collected saliva samples for hormone analysis before and after human–animal interactions and a control condition, and we recorded behavioral data during all conditions. Nasal temperatures consistently decreased for two gorillas during interactions, while the third gorilla showed repeated increases. The behavior of all three gorillas suggested that they were engaged in the interactions, without exhibiting behaviors that could indicate negative welfare impacts. Oxytocin and cortisol both decreased following all conditions, including the control, and were thus equivocal for interpreting the meaning of the changes in nasal temperature. As mixed results in previous research show, infrared thermography may detect emotional arousal; however, additional indicators are necessary to determine the valence of the observed changes. The variability in responses we observed do not lend themselves to making firm conclusions about the validity of infrared thermography (IRT) for measuring emotion in this context or about how these gorillas responded to interactions. Challenges and suggestions for future studies using infrared thermography to examine interactions between humans and zoo animals are discussed.

Abstract

Interactions between zoo professionals and animals occur regularly and are believed to be enriching for animals. Little empirical information exists on how animals perceive these interactions, and particularly how the interactions affect the emotional states of animals. Infrared thermography (IRT) has shown some promise in the assessment of emotions in a variety of species, but further research is needed to determine if this method is useful in a zoo setting. We conducted a pilot study to determine if IRT is a valid measure of the emotional responses to routine interactions (positive reinforcement training and cognitive tasks, compared to a control condition) with familiar humans on three western lowland gorillas at the Detroit Zoo. We measured nasal temperatures associated with emotional change using IRT. To examine the validity of the IRT data, we collected saliva samples for hormone analysis before and after each condition, in addition to behavioral data during the interactions and control condition. Decreases in nasal temperatures for two gorillas and an increase in the third indicate that arousal changed consistently within individuals following the interactions but not the control condition. Pre-post cortisol levels and oxytocin concentrations decreased for all conditions, but the decreases seen did not differ among the conditions. The gorillas were highly engaged in the interactions, and two produced more grumble vocalizations during the human-animal interactions (HAIs) compared to the control condition. Additionally, the gorillas performed self-directed behaviors more often during the control condition, also suggesting HAIs were not a negative experience. In summary, we were able to measure changes in arousal using IRT, but we were unable to determine the emotional valence of these changes based on the additional indicators employed. Additionally, the inconsistency across these measures precluded firm conclusions about either the validity of IRT for measuring emotion in this context or how the interactions impacted these gorillas. These findings highlight the challenges of using IRT to measure emotional states in non-human animals, and we discuss further steps necessary to apply this method in future studies.

Infrared thermography of agonistic behaviour in pigs

Infrared thermography (IRT) or thermal imaging is increasingly being used as a non-invasive method to gain information on animals' physiological and emotional state. IRT has the potential to serve as a non-invasive quantitative assessment method but few studies have examined its utility in predicting welfare-relevant outcomes of dynamic scenarios relevant to commercial farming. This study used 1284 thermal images taken from 46 pigs in a controlled test environment while they engaged in an agonistic encounter (dyadic contest) at 13 wk. of age. Images were taken of the complete body from a dorsal perspective. A pilot study indicated that a rectangular thermal window on the back region was the most suitable and reliable area for obtaining temperature data in this situation. From this thermal window, the average, minimum and maximum temperature, standard deviation and coefficient of variation (CV) were obtained. These were analysed in relation to contest phase (from non-contact assessment, through escalated fighting to retreat), fight occurrence, contest duration, contest outcome (winner/loser status) and changes in blood glucose, blood lactate, and skin injuries. Variables showed a strong change in response to the moment of contest resolution (retreat of the loser); temperatures reduced sharply and CV increased, but did not differ between winners and losers. Contests that included a fight showed lower temperatures. Contest duration, body weight and sex only had minor influences on the temperatures. As the drop in temperature at contest resolution was irrespective of contest intensity, and the pattern was similar in winners and losers, this data potentially reflects vasoconstriction as a result of psychological stress rather than solely a physiological change. The study shows that peripheral temperature, as recorded by IRT, responds to the intensity and phases of a contest and may allow new insight into the physiological and welfare outcomes of aggressive behaviour.

Children with facial paralysis due to Moebius syndrome exhibit reduced autonomic modulation during emotion processing

BACKGROUND

Facial mimicry is crucial in the recognition of others' emotional state. Thus, the observation of others' facial expressions activates the same neural representation of that affective state in the observer, along with related autonomic and somatic responses. What happens, therefore, when someone cannot mimic others' facial expressions?

METHODS

We investigated whether psychophysiological emotional responses to others' facial expressions were impaired in 13 children (9 years) with Moebius syndrome (MBS), an extremely rare neurological disorder (1/250,000 live births) characterized by congenital facial paralysis. We inspected autonomic responses and vagal regulation through facial cutaneous thermal variations and by the computation of respiratory sinus arrhythmia (RSA). These parameters provide measures of emotional arousal and show the autonomic adaptation to others' social cues. Physiological responses in children with MBS were recorded during dynamic facial expression observation and were compared to those of a control group (16 non-affected children, 9 years).

RESULTS

There were significant group effects on thermal patterns and RSA, with lower values in children with MBS. We also observed a mild deficit in emotion recognition in these patients.

CONCLUSION

Results support "embodied" theory, whereby the congenital inability to produce facial expressions induces alterations in the processing of facial expression of emotions. Such alterations may constitute a risk for emotion dysregulation.

Spontaneous attention and psycho-physiological responses to others' injury in chimpanzees

Previous studies have shown that humans experience negative emotions when seeing contextual cues of others' pain, such as injury (i.e., empathic pain), even without observing behavioral expressions of distress. However, this phenomenon has not been examined in nonhuman primates. We tested six chimpanzees (Pan troglodytes) to experimentally examine their reactions to others' injury. First, we measured viewing responses using eye-tracking. Chimpanzees spontaneously attended to injured conspecifics more than non-injured conspecifics, but did not do so in a control condition in which images of injuries were scrambled while maintaining color information. Chimpanzees did not avoid viewing injuries at any point during stimulus presentation. Second, we used thermal imaging to investigate chimpanzees' physiological responses to others' injury. Previous studies reported that reduced nasal temperature is a characteristic of arousal, particularly arousal associated with negative valence. We presented chimpanzees with a realistic injury: a familiar human experimenter with a prosthetic wound and artificial running blood. Chimpanzees exhibited a greater nasal temperature reduction in response to injury compared with the control stimulus. Finally, chimpanzees were presented with a familiar experimenter who stabbed their (fake) thumb with a needle, with no running blood, a situation that may be more challenging in terms of understanding the cause of distress. Chimpanzees did not physiologically distinguish this condition from the control condition. These results suggest that chimpanzees inspect others' injuries and become aroused by seeing injuries even without observing behavioral cues, but have difficulty doing so without explicit (or familiar) cues (i.e., open wound and blood).

Autonomic Responses to Emotional Stimuli in Children Affected by Facial Palsy: The Case of Moebius Syndrome

According to embodied simulation theories, others' emotions are recognized by the unconscious mimicking of observed facial expressions, which requires the implicit activation of the motor programs that produce a specific expression. Motor responses performed during the expression of a given emotion are hypothesized to be directly linked to autonomic responses associated with that emotional behavior. We tested this hypothesis in 9 children (M_age = 5.66) affected by Moebius syndrome (MBS) and 15 control children (M_age = 6.6). MBS is a neurological congenital disorder characterized by underdevelopment of the VI and VII cranial nerves, which results in paralysis of the face. Moebius patients' inability to produce facial expressions impairs their capacity to communicate emotions through the face. We therefore assessed Moebius children's autonomic response to emotional stimuli (video cartoons) by means of functional infrared thermal (fIRT) imaging. Patients showed weaker temperature changes compared to controls, suggesting impaired autonomic activity. They also showed difficulties in recognizing facial emotions from static illustrations. These findings reveal that the impairment of facial movement attenuates the intensity of emotional experience, probably through the diminished activation of autonomic responses associated with emotional stimuli. The current study is the first to investigate emotional responses in MBS children, providing important insights into the role of facial expressions in emotional processing during early development.

Congenital facial palsy and emotion processing: The case of Moebius syndrome

According to the Darwinian perspective, facial expressions of emotions evolved to quickly communicate emotional states and would serve adaptive functions that promote social interactions. Embodied cognition theories suggest that we understand others' emotions by reproducing the perceived expression in our own facial musculature (facial mimicry) and the mere observation of a facial expression can evoke the corresponding emotion in the perceivers. Consequently, the inability to form facial expressions would affect the experience of emotional understanding. In this review, we aimed at providing account on the link between the lack of emotion production and the mechanisms of emotion processing. We address this issue by taking into account Moebius syndrome, a rare neurological disorder that primarily affects the muscles controlling facial expressions. Individuals with Moebius syndrome are born with facial paralysis and inability to form facial expressions. This makes them the ideal population to study whether facial mimicry is necessary for emotion understanding. Here, we discuss behavioral ambiguous/mixed results on emotion recognition deficits in Moebius syndrome suggesting the need to investigate further aspects of emotional processing such as the physiological responses associated with the emotional experience during developmental age.

Emotion analysis in children through facial emissivity of infrared thermal imaging

Physiological signals may be used as objective markers to identify emotions, which play relevant roles in social and daily life. To measure these signals, the use of contact-free techniques, such as Infrared Thermal Imaging (IRTI), is indispensable to individuals who have sensory sensitivity. The goal of this study is to propose an experimental design to analyze five emotions (disgust, fear, happiness, sadness and surprise) from facial thermal images of typically developing (TD) children aged 7–11 years using emissivity variation, as recorded by IRTI. For the emotion analysis, a dataset considered emotional dimensions (valence and arousal), facial bilateral sides and emotion classification accuracy. The results evidence the efficiency of the experimental design with interesting findings, such as the correlation between the valence and the thermal decrement in nose; disgust and happiness as potent triggers of facial emissivity variations; and significant emissivity variations in nose, cheeks and periorbital regions associated with different emotions. Moreover, facial thermal asymmetry was revealed with a distinct thermal tendency in the cheeks, and classification accuracy reached a mean value greater than 85%. From the results, the emissivity variations were an efficient marker to analyze emotions in facial thermal images, and IRTI was confirmed to be an outstanding technique to study emotions. This study contributes a robust dataset to analyze the emotions of 7-11-year-old TD children, an age range for which there is a gap in the literature.

Detecting changes in facial temperature induced by a sudden auditory stimulus based on deep learning-assisted face tracking

Thermal Imaging (Infrared-Imaging-IRI) is a promising new technique for psychophysiological research and application. Unlike traditional physiological measures (like skin conductance and heart rate), it is uniquely contact-free, substantially enhancing its ecological validity. Investigating facial regions and subsequent reliable signal extraction from IRI data is challenging due to head motion artefacts. Exploiting its potential thus depends on advances in analytical methods. Here, we developed a novel semi-automated thermal signal extraction method employing deep learning algorithms for facial landmark identification. We applied this method to physiological responses elicited by a sudden auditory stimulus, to determine if facial temperature changes induced by a stimulus of a loud sound can be detected. We compared thermal responses with psycho-physiological sensor-based tools of galvanic skin response (GSR) and electrocardiography (ECG). We found that the temperatures of selected facial regions, particularly the nose tip, significantly decreased after the auditory stimulus. Additionally, this response was quite rapid at around 4–5 seconds, starting less than 2 seconds following the GSR changes. These results demonstrate that our methodology offers a sensitive and robust tool to capture facial physiological changes with minimal manual intervention and manual pre-processing of signals. Newer methodological developments for reliable temperature extraction promise to boost IRI use as an ecologically-valid technique in social and affective neuroscience.

Regional differences in facial skin blood flow responses to thermal stimulation

PURPOSE

The facial skin blood flow (SkBF) shows regional differences in the responses to a given stimulation. The facial SkBFs, especially in the eyelid and nose exhibit unique response to physiological and psychological stimuli, but the mechanisms inducing those regional differences remain unclear. To investigate whether the regional differences in the local control of vasomotion in facial vessels correspond to the regional differences in facial SkBF response, we monitored the relative change of facial SkBF to regional thermal stimulation. We hypothesized that heat stimulation dilates the cutaneous vessels in the eyelid, while cold stimulation constricts those in the nose, which was based on previous findings METHODS: A thermal stimulator was used to apply temperature increase (from 20 to 40 °C at 2 °C/min) and decrease (from 40 to 20 °C at 2°C/min) in a randomized order to the right eyelid, nose, right cheek, and forehead of 14 healthy young males. The facial SkBF was measured for 10 s using laser-speckle flowgraphy when temperatures of 20 °C, 30 °C, and 40 °C had been applied for 30 s in both trials.

RESULTS

The SkBF in the eyelid did not change significantly during any thermal stimulation, and the nasal SkBF did not decrease significantly during cold stimulation. The SkBFs in the cheek and forehead increased significantly with the applied temperature.

CONCLUSIONS

These findings indicate that a large regional variation exists in facial skin blood flow response to local heating or cooling and that the regional variation did not correspond to the unique SkBF responses in the previous studies.

Daily rhythms of rectal and body surface temperatures in donkeys during the cold-dry (harmattan) and hot-dry seasons in a tropical savannah

The aim of the study was to evaluate daily rhythms of rectal temperature (RT) and body surface temperature (BST) of adult, yearling and foal donkeys during the cold-dry (harmattan) and hot-dry seasons in a tropical savanna. The RTs and BSTs of 30 clinically healthy, free-ranging donkeys were recorded using digital and infrared thermometers. The RT and BST of each donkey and thermal environmental parameters inside the pen were measured bi-hourly from 0600 to 0600 hours (GM + 1) on each experimental day. Application of single cosinor procedure showed that RT and BST exhibited varying levels of daily rhythmicity in both seasons, with values usually higher during the afternoon periods of the photophase of the light/dark cycle. The oscillatory pattern differed with season, with greater amplitude recorded during the cold-dry season than the hot-dry season. The acrophases of the RT and BST were mostly restricted to the photophase of the light/dark cycle in both seasons. The mean values of RT in the adult (37.10 ± 0.10 °C), yearling (37.19 ± 0.10 °C) and foal (37.45 ± 0.11 °C) donkeys were higher (F = 93.41, P < 0.0001) during the hot-dry season than the cold-dry season (35.40 ± 0.05 °C, 35.50 ± 0.04 °C and 36.20 ± 0.05 °C, respectively). In conclusion, seasonal changes influenced significantly the daily rhythmicity of RT and BST in donkeys, kept under natural light/dark cycle.

The Impact of 'Selfie' Tourism on the Behaviour and Welfare of Brown-Throated Three-Toed Sloths

Simple Summary

The use of wild animals as photo props is a potential animal welfare concern that is prevalent across Latin America. The present study documents animal welfare concerns associated with the use of wild caught brown-throated three-toed sloths (Bradypus variegatus) for wildlife ‘selfies’ by tourists at three locations in Manaus, Brazil and Puerto Alegria and Iquitos in Peru. Between 4 October 2016 and 8 April 2017 researchers attended 34 tours, where 17 sloths were observed. The sloths were; (1) held on average by 5 people (during each observation); (2) frequently exposed to physical manipulation of the head and/or limbs; and (3) frequently held by their claws. During handling the sloth’s behaviour was also analysed; we found that the two behaviours performed for the longest average duration of time were surveillance (55.3%) and limb stretching (12.6%). Further validation is needed; however, it is possible that some of the behaviours displayed may be indicators of fear, stress and anxiety. Our results describe behaviours exhibited by sloths, which have previously never been documented in any published literature, the data therefore serves as a potential baseline for future study.

Abstract

The use of wild animals as photo props is prevalent across the globe and is widely recognised to represent a potential animal welfare concern. However, detailed information regarding the specific impacts of such activity on wild animal behaviour is currently lacking. Herein, we investigated how brown-throated three-toed sloths (Bradypus variegatus) were handled by tourists, and how sloths behaved during wildlife ‘selfies’ taken in Manaus, Brazil and Puerto Alegria and Iquitos in Peru. In total, we observed 17 sloths (during 70 focal observations) that were provided for use in wildlife selfies on 34 different tours. We found that an average number of 5 people held each sloth during each focal observation. For 48.6% of the time the sloths were handled in a way which involved physical manipulation of the sloths’ head and/or limbs and/or being held by the claws. From the eight different types of sloth behaviour observed, we found that the two types performed for the longest average duration of time were surveillance (55.3%) and limb stretching (12.6%). Our findings show that when being handled sloths were frequently held in ways that may compromise their welfare. Although to date the behaviour of sloths while being handled has not been reported in any published literature, in this study we document certain behaviours which may act as indicators of compromised welfare. We suggest that our data provides a potential baseline for future study into the behaviour and welfare of sloths.

Thermography as a Non-Invasive Measure of Stress and Fear of Humans in Sheep

Simple Summary

The ability to non-invasively measure fear is an essential component of animal welfare assessment. Infrared thermography (IRT) was used to obtain images from five Sarda breed ewes during restraint and immediately after two voluntary animal approach (VAA) tests. Our preliminary results suggest that IRT, combined with behavioral data, is a non-invasive technique that can be useful to assess stress and infer about negative emotions in sheep.

Abstract

No data have been published on the use of infrared thermography (IRT) to evaluate sheep emotions. We assessed whether this technique can be used as a non-invasive measure of negative emotions. Two voluntary animal approach (VAA) tests were conducted (and filmed) on five ewes before and after being restrained. The restraining process was performed by a handler for five minutes. IRT was used during restraint and the VAA tests. The lacrimal caruncle temperature was significantly higher during restraint and in the VAA test after the restraint compared with the VAA test before the restraint (Wilcoxon’s test; p = 0.04). The latency period until first contact was longer in the second VAA test (132 s) than in the first one (60 s). Our preliminary results suggest that IRT, combined with behavioral data, is a non-invasive technique that can be useful to assess stress and infer about negative emotions in sheep.

Infrared thermal imaging: Positive and negative emotions modify the skin temperatures of monkey and ape faces

Facial thermography has enabled researchers to noninvasively and continuously measure the changes of a range of emotional states in humans. The present work used this novel technology to study the effect of positive and negative emotions in nonhuman primates by focusing on four facial areas (the peri-orbital area, the nose bridge, the nose tip, and the upper lip). Monkeys and apes were examined for positive emotions (during interactions with toys and during tickling) and for negative emotions (during food delay and teasing). For the combined toy and tickling condition, the results indicated a drop in the nose tip temperature and a tendency of an increase in the peri-orbital temperature. For the combined food delay and teasing condition, the results also revealed a rise in the upper lip temperature of the subjects. These different effects on the facial temperatures in monkeys and apes most likely reflect distinctive physiological reactions of a primordial primate emotion system. We conclude that facial thermal imaging represents a promising physiologically grounded technology to noninvasively and continuously obtain reliable data on emotional states in nonhuman primates, which may help modernize research on emotions in nonhuman primates and enhance our understanding of the evolution of human emotions.

Thermal facial reactivity patterns predict social categorization bias triggered by unconscious and conscious emotional stimuli

Members of highly social species decode, interpret, and react to the emotion of a conspecific depending on whether the other belongs to the same (ingroup) or different (outgroup) social group. While studies indicate that consciously perceived emotional stimuli drive social categorization, information about how implicit emotional stimuli and specific physiological signatures affect social categorization is lacking. We addressed this issue by exploring whether subliminal and supraliminal affective priming can influence the categorization of neutral faces as ingroup versus outgroup. Functional infrared thermal imaging was used to investigate whether the effect of affective priming on the categorization decision was moderated by the activation of the sympathetic nervous system (SNS). During the subliminal condition, we found that stronger SNS activation after positive or negative affective primes induced ingroup and outgroup face categorization, respectively. The exact opposite pattern (i.e. outgroup after positive and ingroup after negative primes) was observed in the supraliminal condition. We also found that misattribution effects were stronger in people with low emotional awareness, suggesting that this trait moderates how one recognizes SNS signals and employs them for unrelated decisions. Our results allow the remarkable implication that low-level affective reactions coupled with sympathetic activation may bias social categorization.