A Continuously Worn Dual Temperature Sensor System for Accurate Monitoring of Core Body Temperature from the Ear Canal.

The objective of this work was to develop a temperature sensor system that accurately measures core body temperature from an ear-worn device. Two digital temperature sensors were embedded in a hearing aid shell along the thermal gradient of the ear canal to form a linear heat balance relationship. This relationship was used to determine best fit parameters for estimating body temperature. The predicted body temperatures resulted in intersubject limits of agreement (LOA) of ±0.49 °C over a range of physiologic and ambient temperatures without calibration. The newly developed hearing aid-based temperature sensor system can estimate core body temperature at an accuracy level equal to or better than many devices currently on the market. An accurate, continuously worn, temperature monitoring and tracking device may help provide early detection of illnesses, which could prove especially beneficial during pandemics and in the elderly demographic of hearing aid wearers.

Risk factors for intraoperative hypothermia in infants during general anesthesia: A retrospective study.

This study aimed to determine the incidence and evaluate the risk factors and outcomes of intraoperative hypothermia (IH) during general anesthesia in infants. Retrospective analysis of prospectively collected data. A total of 754 infants younger than 1 year old who underwent surgery under general anesthesia were included. Intraoperative body temperature fluctuations, surgical and anesthetic data, postoperative complications, and infant outcomes were recorded. Logistic regression algorithms were used to evaluate potential risk factors. Among the 754 infants, 47.88% developed IH (<36 °C) and 15.4% of them experienced severe hypothermia (<35 °C). The average lowest temperature in hypothermia patients was 35.06 ± 0.69°C with a duration of 82.23 ± 50.59 minutes. Neonates tended to experience hypothermia (37.7% vs 7.6%, P < .001) and prematurity was more common in patients with IH (29.4% vs 16.8%, P < .001). Infants with hypothermia experienced a longer length of stay in the post anesthesia care units and intensive care units, postoperative hospitalizations, and tracheal extubation as well as a higher rate of postoperative hemorrhage than those with normothermia (all P < .05). Several factors were proved to be associated with an increased risk of IH after multivariate analysis: neonate (odds ratio [OR] = 3.685, 95% CI 1.839-7.382), weight (OR = 0.599, 95% CI 0.525-0.683), American society of anesthesiologists (OR = 3.418, 95% CI 2.259-5.170), fluid > 20 mL/kg (OR = 2.380, 95% CI 1.389-4.076), surgery time >60 minutes (OR = 1.785, 95% CI 1.030-3.093), and pre-warming (OR = 0.027, 95% CI 0.014-0.052). This retrospective study found that neonates, lower weight, longer surgery times, more fluid received, higher American society of anesthesiologists stage, and no pre-warming were all significant risk factors for IH during general anesthesia in infants.

Reduction in the duration of postoperative fever following NUSS surgery during the COVID-19 pandemic.

BACKGROUND: Our study aimed to compare the prevalence of postoperative fever during the COVID-19 pandemic period with that of the preceding non-pandemic period. METHODS: A retrospective analysis was conducted on patients with pectus excavatum (PE) undergoing minimally invasive repair (also called NUSS procedure) at Nanjing Children's Hospital from January 1, 2017 to March 1, 2019 (Group 2019), and from January 1, 2020 to March 1, 2021 (Group 2021). Data from a total of 284 patients, consisting of 200 (70.4%) males and 84 (29.6%) females with an average age of 9.73 ± 3.41 (range, 4 to 17) years, were collected. The presence of post-operative fever (defined as a forehead temperature of 37.5℃ or above within 72 h post-surgery), as well as the time of operation, duration of postoperative mechanical ventilator and urinary catheter use, and length of hospitalization were all assessed in admitted patients from Group 2019 (n = 144) and Group 2021 (n = 140). Postoperative white blood cell (WBC), C-reactive protein (CRP) levels, and prevalence of postoperative complications (i.e., pneumothorax, pulmonary atelectasis, pneumonia, wound infection, and dehiscence) were also determined. RESULT: Our results showed a statistically significant decrease in the incidence of postoperative fever within 24 to 72 h of surgery in patients admitted from Group 2019 as compared to Group 2021 (p < 0.001), as well as a decrease in peak body temperature within 72 h (p < 0.05). Meanwhile, no significant differences were observed in age and body mass index (BMI), time of operation, or duration of postoperative mechanical ventilator and urinary catheter use between the two groups (p > 0.05). The average hospitalization length of Group 2021 was significantly shorter than Group 2019 (12.49 ± 2.57 vs. 11.85 ± 2.19 days, p < 0.05). Furthermore, while the WBC count between the two groups 24 h after surgery showed a statistical difference (p < 0.05), no differences in CRP levels or the incidence of postoperative complications were observed (p > 0.05). CONCLUSION: The prevalence of postoperative fever within 72 h of surgery and the length of hospital stay for patients with PE undergoing NUSS surgery were both decreased in Group 2021. We propose that the above phenomenon may be related to increased used of personal protection equipment (such as surgical masks and filtering facepiece respirators (FFRs)) by physicians, nurses, and the patients themselves.

Copulatory courtship, body temperature and infection in Tenebrio molitor.

Ectothermic animals can raise their body temperature under varying circumstances. Two such situations occur during sexual activity (as metabolic rate rises during copulatory movements) and during infection (to control pathogens more effectively). We have investigated these two situations using Tenebrio molitor males. We recorded the copulatory courtship behavior of sick (= infected with Metharizium robertsii fungus) vs healthy males and its link with body temperature. We predicted a positive relation between copulatory courtship (measured as antennal and leg contact behavior) and body temperature, especially in sick males. We found that the intensity of contacts correlated with increased body temperature in sick males. Previous studies in this species indicated that partner females laid fewer eggs after mating with sick males above a certain male body temperature threshold. Thus, our present findings suggest that females may detect male infection via intensity of antennal-mediated courtship, body temperature or their combination. If this is the case, females may assess male cues directly related to health status such as body temperature.

Pre-analytical variables influence zinc measurement in blood samples.

Zinc deficiency continues to be a major concern for global public health. The zinc status of a target population is typically estimated by measuring circulating zinc levels, but the sampling procedures are not standardized and thus may result in analytical discrepancies. To examine this, we designed a study that controlled most of the technical parameters in order to focus on five pre-analytical variables reported to influence the measurement of zinc in blood samples, including (1) blood draw site (capillary or venous), (2) blood sample matrix (plasma or serum), (3) blood collection tube manufacturer (Becton, Dickinson and Company or Sarstedt AG & Co), (4) blood processing time (0, 4, or 24 hours), and (5) blood holding temperatures (4°C, 20°C, or 37°C). A diverse cohort of 60 healthy adults were recruited to provide sequential capillary and venous blood samples, which were carefully processed under a single chain of custody and measured for zinc content using inductively coupled plasma optical emission spectrometry. When comparing blood draw sites, the mean zinc content of capillary samples was 0.054 mg/L (8%; p<0.0001) higher than venous blood from the same donors. When comparing blood sample matrices, the mean zinc content of serum samples was 0.029 mg/L (5%; p<0.0001) higher than plasma samples from the same donors. When comparing blood collection tube manufacturer, the mean zinc content from venous blood samples did not differ between venders, but the mean zinc content from BD capillary plasma was 0.036 mg/L (6%; p<0.0001) higher than Sarstedt capillary plasma from the same donors. When comparing processing times, the mean zinc content of plasma and serum samples was 5-12% higher (p<0.0001) in samples processed 4-24 hour after collection. When comparing holding temperatures, the mean zinc content of plasma and serum samples was 0.5-7% higher (p = 0.0007 or p = 0.0061, respectively) in samples temporarily held at 20°C or 37°C after collection. Thus even with the same donors and blood draws, significant differences in zinc content were observed with different draw sites, tube types, and processing procedures, demonstrating that key pre-analytic variables can have an impact on zinc measurement, and subsequent classification of zinc status. Minimizing these pre-analytical variables is important for generating best practice guidelines for assessment of zinc status.

Predictive models for short-term mortality and length of hospital stay among adults with community-onset bacteraemia before and during the COVID-19 pandemic: application of early data dynamics.

BACKGROUND: The development of scoring systems to predict the short-term mortality and the length of hospital stay (LOS) in patients with bacteraemia is essential to improve the quality of care and reduce the occupancy variance in the hospital bed. METHODS: Adults hospitalised with community-onset bacteraemia in the coronavirus disease 2019 (COVID-19) and pre-COVID-19 eras were captured as the validation and derivation cohorts in the multicentre study, respectively. Model I incorporated all variables available on day 0, Model II incorporated all variables available on day 3, and Models III, IV, and V incorporated the variables that changed from day 0 to day 3. This study adopted the statistical and machine learning (ML) methods to jointly determine the prediction performance of these models in two study cohorts. RESULTS: A total of 3,639 (81.4%) and 834 (18.6%) patients were included in the derivation and validation cohorts, respectively. Model IV achieved the best performance in predicting 30-day mortality in both cohorts. The most frequently identified variables incorporated into Model IV were deteriorated consciousness from day 0 to day 3 and deteriorated respiration from day 0 to day 3. Model V achieved the best performance in predicting LOS in both cohorts. The most frequently identified variables in Model V were deteriorated consciousness from day 0 to day 3, a body temperature ≤ 36.0 °C or ≥ 39.0 °C on day 3, and a diagnosis of complicated bacteraemia. CONCLUSIONS: For hospitalised adults with community-onset bacteraemia, clinical variables that dynamically changed from day 0 to day 3 were crucial in predicting the short-term mortality and LOS.

Non-Contact Infrared Thermometers and Thermal Scanners for Human Body Temperature Monitoring: A Systematic Review.

In recent years, non-contact infrared thermometers (NCITs) and infrared thermography (IRT) have gained prominence as convenient, non-invasive tools for human body temperature measurement. Despite their widespread adoption in a range of settings, there remain questions about their accuracy under varying conditions. This systematic review sought to critically evaluate the performance of NCITs and IRT in body temperature monitoring, synthesizing evidence from a total of 72 unique settings from 32 studies. The studies incorporated in our review ranged from climate-controlled room investigations to clinical applications. Our primary findings showed that NCITs and IRT can provide accurate and reliable body temperature measurements in specific settings and conditions. We revealed that while both NCITs and IRT displayed a consistent positive correlation with conventional, contact-based temperature measurement tools, NCITs demonstrated slightly superior accuracy over IRT. A total of 29 of 50 settings from NCIT studies and 4 of 22 settings from IRT studies achieved accuracy levels within a range of ±0.3 °C. Furthermore, we found that several factors influenced the performance of these devices. These included the measurement location, the type of sensor, the reference and tool, individual physiological attributes, and the surrounding environmental conditions. Our research underscores the critical need for further studies in this area to refine our understanding of these influential factors and to develop standardized guidelines for the use of NCITs and IRT.

[Application of body temperature rinse in percutaneous transforaminal endoscopic lumbar discectomy through intervertebral approach].

OBJECTIVE: To investigate the effects of two types of temperature rinses on body temperature, inflammatory cytokine levels, and bleeding volume in percutaneous endoscopic lumbar discectomy. METHODS: Eighty patients underwent percutaneous endoscopic lumbar discectomy from January 2018 to December 2020 were selected and divided into experimental group (40 cases) and control group(40 cases). In experimental group, there were 19 males and 21 females, aged (38.8±9.8) years old;7patients on L4,5 and 33 patients on L5S1;Body msss index(BMI) was (27.8±7.2) kg·m-2. In contral group, there were 18 males and 22 females, aged (41.5±10.9) years old, 5 patients on L4,5 and 35 patients on L5S1;BMI was (26.4±6.2) kg·m-2. The patients in the control group were received normal saline rinse at room temperature, and the patients in the experimental group were received normal saline rinse heated to 37 ℃. Body temperature, chills, nausea, vomiting, and other adverse reactions were recorded. The levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-10 (IL-10) in two groups were recorded before and 2 hours after operation. Visual analogue scale (VAS) was used to evaluate the degree of lumbar pain in two groups before and 2 hours after surgery. Fibrinolytic-coagulation indexes with preoperative and 2 hours after surgery, including the D-dimer (DD), fibrinogen degradation products (FDP), activated partial thrombin time (APTT) and prothrombin time (PT) were recorder. Operation time and blood loss in two groups were recorded. RESULTS: The body temperature of both groups showed a downward trend, while the body temperature of the control group was lower than that of the experimental group. The levels of TNF-α, IL-6 and IL-10 in two groups were increased 2 hours after surgery compared with those before surgery(P<0.05), while the levels in experimental group were lower than those in control group(P<0.05). Postoperative VAS in experimental group 2.19±1.13 was significantly lower than that in the control group 3.38±1.35(P<0.05). The levels of DD and FDP at 2 hours after surgery in both groups were higher than those before surgery (P<0.05), while the levels of DD and FDP in the experimental group were higher than those in the control group (P<0.05). There was no significant difference in APTT and PT levels between two groups after operation (P>0.05). The blood loss in the experimental group of (45.2±14.1) ml was lower than that in the control group of (59.52±15.6) ml. The operation time of experimental group (46.7±13.8) min was less than that of control group (58.3±15.2) min(P<0.05). CONCLUSION: Body temperature rinse can reduce the incidence of adverse reactions, alleviate local inflammatory reactions, reduce intraoperative blood loss and shorten the operation time.

Effects of bathing-induced changes in body temperature on sleep.

BACKGROUND: Passive body heating before sleep is well known to lead to improved sleep. However, the effects of the degree of change in body temperature by bathing on sleep quality are unclear. The present study aimed to clarify the effects on sleep of bathing-induced changes in body temperature. METHODS: Twenty-three healthy males and females in their 20 s to 50 s bathed in their homes 1.5-2 h before bedtime under three bathing conditions: showering only; short bathing in a bathtub; and long bathing in a bathtub. Sublingual and skin temperatures and thermal sensation before and after bathing, sleep indices such as sleep onset latency, time in bed, sleep efficiency, and wake after sleep onset, all of which were evaluated using an actimeter, and subjective evaluations of sleep were compared among conditions. RESULTS: Sublingual temperature just after bathing was significantly higher with long bathing than with other conditions, and the fall in sublingual temperature from after bathing to before sleep was significantly larger with long bathing than with short bathing. Sleep onset latency by actimeter was significantly reduced with long bathing compared to showering. In addition, subjective evaluations of falling asleep and sleep quality were better with long bathing than with showering or short bathing. CONCLUSIONS: In conclusion, bathing conditions that produce a 0.9 °C increase in sublingual temperature appear effective for falling asleep and sleep quality, because core temperature shows a greater drop to before sleep than those producing an increase of about 0.3 °C increase in sublingual temperature.

Impact of Clinical Study Implementation on Data Quality Assessments - Using Contradictions within Interdependent Health Data Items as a Pilot Indicator.

INTRODUCTION: Contradiction is a relevant data quality indicator to evaluate the plausibility of interdependent health data items. However, while contradiction assessment is achieved using domain-established contradictory dependencies, recent studies have shown the necessity for additional requirements to reach conclusive contradiction findings. For example, the oral or rectal methods used in measuring the body temperature will influence the thresholds of fever definition. The availability of this required information as explicit data items must be guaranteed during study design. In this work, we investigate the impact of activities related to study database implementation on contradiction assessment from two perspectives including: 1) additionally required metadata and 2) implementation of checks within electronic case report forms to prevent contradictory data entries. METHODS: Relevant information (timestamps, measurement methods, units, and interdependency rules) required for contradiction checks are identified. Scores are assigned to these parameters and two different studies are evaluated based on the fulfillment of the requirements by two selected interdependent data item sets. RESULTS: None of the studies have fulfilled all requirements. While timestamps and measurement units are found, missing information about measurement methods may impede conclusive contradiction assessment. Implemented checks are only found if data are directly entered. DISCUSSION: Conclusive contradiction assessment typically requires metadata in the context of captured data items. Consideration during study design and implementation of data capture systems may support better data quality in studies and could be further adopted in primary health information systems to enhance clinical anamnestic documentation.

Towards substitution of invasive telemetry: An integrated home cage concept for unobtrusive monitoring of objective physiological parameters in rodents.

This study presents a novel concept for a smart home cage design, tools, and software used to monitor the physiological parameters of mice and rats in animal-based experiments. The proposed system focuses on monitoring key clinical parameters, including heart rate, respiratory rate, and body temperature, and can also assess activity and circadian rhythm. As the basis of the smart home cage system, an in-depth analysis of the requirements was performed, including camera positioning, imaging system types, resolution, frame rates, external illumination, video acquisition, data storage, and synchronization. Two different camera perspectives were considered, and specific camera models, including two near-infrared and two thermal cameras, were selected to meet the requirements. The developed specifications, hardware models, and software are freely available via GitHub. During the first testing phase, the system demonstrated the potential of extracting vital parameters such as respiratory and heart rate. This technology has the potential to reduce the need for implantable sensors while providing reliable and accurate physiological data, leading to refinement and improvement in laboratory animal care.

Recent advances in insect thermoregulation.

Ambient temperature (Ta) is a critical abiotic factor for insects that cannot maintain a constant body temperature (Tb). Interestingly, Ta varies during the day, between seasons and habitats; insects must constantly cope with these variations to avoid reaching the deleterious effects of thermal stress. To minimize these risks, insects have evolved a set of physiological and behavioral thermoregulatory processes as well as molecular responses that allow them to survive and perform under various thermal conditions. These strategies range from actively seeking an adequate environment, to cooling down through the evaporation of body fluids and synthesizing heat shock proteins to prevent damage at the cellular level after heat exposure. In contrast, endothermy may allow an insect to fight parasitic infections, fly within a large range of Ta and facilitate nest defense. Since May (1979), Casey (1988) and Heinrich (1993) reviewed the literature on insect thermoregulation, hundreds of scientific articles have been published on the subject and new insights in several insect groups have emerged. In particular, technical advancements have provided a better understanding of the mechanisms underlying thermoregulatory processes. This present Review aims to provide an overview of these findings with a focus on various insect groups, including blood-feeding arthropods, as well as to explore the impact of thermoregulation and heat exposure on insect immunity and pathogen development. Finally, it provides insights into current knowledge gaps in the field and discusses insect thermoregulation in the context of climate change.

InfraNet: Accurate forehead temperature measurement framework for people in the wild with monocular thermal infrared camera.

During an epidemic, accurate human temperature screening based on neural networks for disease surveillance is important and challenging. Existing distant human forehead temperature measuring device usually adopts a dual-camera system using paired RGB and thermal infrared images to conduct face detection and temperature measurement. Since the facial RGB image may undermine people's privacy, we designed a monocular thermal system and proposed an effective framework called the InfraNet to measure and calibrate forehead temperature of people in the wild. To address the challenge of temperature floating, the InfraNet calibrates the subject's temperature with one's physical depth and horizontal offset predicted by a single infrared image. Our InfraNet framework mainly consists of three parts: face detection subnet, depth and horizontal offset estimation subnet and temperature calibration subnet. The temperature calibration performance can be improved with the help of spatial regularization term concentrating on predicting precise depth and horizontal offset of people. Besides, we collected a large-scale infrared image dataset in the both lab and wild scenarios, including 8,215 thermal infrared images. Experiments on our wild dataset demonstrated that the InfraNet achieved 91.6% high accuracy of distant multi-subject temperature measurement on average under the standard temperature threshold of strict 0.3°C.

A brainstem to circadian system circuit links Tau pathology to sundowning-related disturbances in an Alzheimer's disease mouse model.

Alzheimer's disease (AD) patients exhibit progressive disruption of entrained circadian rhythms and an aberrant circadian input pathway may underlie such dysfunction. Here we examine AD-related pathology and circadian dysfunction in the APPSwe-Tau (TAPP) model of AD. We show these mice exhibit phase delayed body temperature and locomotor activity with increases around the active-to-rest phase transition. Similar AD-related disruptions are associated with sundowning, characterized by late afternoon and early evening agitation and aggression, and we show TAPP mice exhibit increased aggression around this transition. We show such circadian dysfunction and aggression coincide with hyperphosphorylated Tau (pTau) development in lateral parabrachial (LPB) neurons, with these disturbances appearing earlier in females. Finally, we show LPB neurons, including those expressing dynorphin (LPBdyn), project to circadian structures and are affected by pTau, and LPBdyn ablations partially recapitulate the hyperthermia of TAPP mice. Altogether we link pTau in a brainstem circadian input pathway to AD-related disturbances relevant to sundowning.

Wolbachia has subtle effects on thermal preference in highly inbred Drosophila melanogaster which vary with life stage and environmental conditions.

Temperature fluctuations are challenging for ectotherms which are not able to regulate body temperature by physiological means and thus have to adjust their thermal environment via behavior. However, little is yet known about whether microbial symbionts influence thermal preference (Tp) in ectotherms by modulating their physiology. Several recent studies have demonstrated substantial effects of Wolbachia infections on host Tp in different Drosophila species. These data indicate that the direction and strength of thermal preference variation is strongly dependent on host and symbiont genotypes and highly variable among studies. By employing highly controlled experiments, we investigated the impact of several environmental factors including humidity, food quality, light exposure, and experimental setup that may influence Tp measurements in adult Drosophila melanogaster flies. Additionally, we assessed the effects of Wolbachia infection on Tp of Drosophila at different developmental stages, which has not been done before. We find only subtle effects of Wolbachia on host Tp which are strongly affected by experimental variation in adult, but not during juvenile life stages. Our in-depth analyses show that environmental variation has a substantial influence on Tp which demonstrates the necessity of careful experimental design and cautious interpretations of Tp measurements together with a thorough description of the methods and equipment used to conduct behavioral studies.

[Research progress of target temperature management on protective mechanism of cardiac function after cardiac arrest].

Targeted temperature management (TTM) has been partially applied in patients with restoration of spontaneous circulation (ROSC) after cardiac arrest (CA). In the 2020 American Heart Association (AHA) cardiopulmonary resuscitation (CPR) guidelines, TTM is used as advanced life support after ROSC for the treatment of patients with CPR. TTM has a protective effect on cardiac function after CA, but the specific mechanism of its protective effect on cardiac function remains unclear. In this paper, the basic experimental progress, clinical trial progress and development prospect of TTM on the protective mechanism of cardiac function after CA are reviewed.

Inadvertent Perioperative Hypothermia.

Temperature regulation during the perioperative period plays an essential role in keeping patients safe while optimizing their recovery. The World Health Organization recommends preserving normothermia, identified as a core body temperature greater than 36°C, to minimize morbidity and mortality. The etiology of inadvertent perioperative hypothermia (IPH) varies in origin. Preoperative exposure, decreased ambient operating room (OR) temperature, skin exposure during preparation, unwarmed skin preparation and washout solutions, and lack of warming devices all contribute to IPH. Moreover, general and regional anesthesia blunt the physiologic response to hypothermia which originates in the hypothalamus. Postoperatively, patients with temperatures < 36°C are at greater risk for surgical site infection, increased mortality, longer length of hospital stay, higher 30-day readmission rates, among other complications. Identifying preoperative risk factors and OR practices that contribute to IPH, monitoring temperatures, and use of warming devices during the perioperative period can help to prevent IPH.

Efficient assessment of real-world dynamics of circadian rhythms in heart rate and body temperature from wearable data.

Laboratory studies have made unprecedented progress in understanding circadian physiology. Quantifying circadian rhythms outside of laboratory settings is necessary to translate these findings into real-world clinical practice. Wearables have been considered promising way to measure these rhythms. However, their limited validation remains an open problem. One major barrier to implementing large-scale validation studies is the lack of reliable and efficient methods for circadian assessment from wearable data. Here, we propose an approximation-based least-squares method to extract underlying circadian rhythms from wearable measurements. Its computational cost is ∼ 300-fold lower than that of previous work, enabling its implementation in smartphones with low computing power. We test it on two large-scale real-world wearable datasets: [Formula: see text] of body temperature data from cancer patients and ∼ 184 000 days of heart rate and activity data collected from the 'Social Rhythms' mobile application. This shows successful extraction of real-world dynamics of circadian rhythms. We also identify a reasonable harmonic model to analyse wearable data. Lastly, we show our method has broad applicability in circadian studies by embedding it into a Kalman filter that infers the state space of the molecular clocks in tissues. Our approach facilitates the translation of scientific advances in circadian fields into actual improvements in health.

Light phase does not affect operant sucrose self-administration in adult male C57BL/6JAbr mice.

Circadian rhythm can have significant impacts on several physiological domains relevant to the expression of behaviour in mice, including body temperature, corticosterone levels, hormones and immune function. Mice are nocturnal; yet many behavioural studies are performed during the light phase, when mice are naturally inactive. Not surprisingly, the time of day when mice are behaviourally tested can significantly impact on domains such as locomotor activity, e.g. dark phase testing results in higher locomotion rates than light phase testing. However, effects on other behavioural domains, such as cognition, are not well-established, with inconsistent reports on improved cognition during dark phase testing compared to light phase testing in mice. Importantly, the impact of circadian rhythm on operant responding, a common task relevant to research into drug abuse and cognitive disorders, has rarely been investigated in mice. Here we evaluated if testing adult male C57BL/6JAbr mice in operant chambers during the light or dark phase affects acquisition of lever responding, lever discrimination under different fixed ratio (FR) schedules (FR1, FR2, FR4), and/or motivation under a progressive ratio schedule for 10% oral sucrose. We found no effect of circadian rhythm on levels of active and inactive lever pressing, or lever discrimination for oral sucrose at any stage of the experiment. These results may be due to high levels of motivation for sucrose under food restriction and low levels of task complexity limiting detection of any effect of light phase on operant behaviour.

Xiphoid nucleus of the midline thalamus controls cold-induced food seeking.

Maintaining body temperature is calorically expensive for endothermic animals1. Mammals eat more in the cold to compensate for energy expenditure2, but the neural mechanism underlying this coupling is not well understood. Through behavioural and metabolic analyses, we found that mice dynamically switch between energy-conservation and food-seeking states in the cold, the latter of which are primarily driven by energy expenditure rather than the sensation of cold. To identify the neural mechanisms underlying cold-induced food seeking, we used whole-brain c-Fos mapping and found that the xiphoid (Xi), a small nucleus in the midline thalamus, was selectively activated by prolonged cold associated with elevated energy expenditure but not with acute cold exposure. In vivo calcium imaging showed that Xi activity correlates with food-seeking episodes under cold conditions. Using activity-dependent viral strategies, we found that optogenetic and chemogenetic stimulation of cold-activated Xi neurons selectively recapitulated food seeking under cold conditions whereas their inhibition suppressed it. Mechanistically, Xi encodes a context-dependent valence switch that promotes food-seeking behaviours under cold but not warm conditions. Furthermore, these behaviours are mediated by a Xi-to-nucleus accumbens projection. Our results establish Xi as a key region in the control of cold-induced feeding, which is an important mechanism in the maintenance of energy homeostasis in endothermic animals.