The molecular clockwork of mammalian cells.

Most organisms contain self-sustained circadian clocks. These clocks can be synchronized by environmental stimuli, but can also oscillate indefinitely in isolation. In mammals this is true at the molecular level for the majority of cell types that have been examined. A core set of "clock genes" form a transcriptional/translational feedback loop (TTFL) which repeats with a period of approximately 24 h. The exact mechanism of the TTFL differs slightly in various cell types, but all involve similar family members of the core cohort of clock genes. The clock has many outputs which are unique for different tissues. Cells in diverse tissues will convert the timing signals provided by the TTFL into uniquely orchestrated transcriptional oscillations of many clock-controlled genes and cellular processes.

Reassessment of arterial versus venous perfusion of diabetic retinal neovascularization using ultrawide-field fluorescein angiography.

PURPOSE: The purpose of this study was to assess whether diabetic NV is perfused by the arterial or the venous circulation. METHODS: This is a retrospective, consecutive case series evaluating patients with proliferative diabetic retinopathy (PDR) imaged with ultrawide-field (UWF) fluorescein angiography (FA). Areas of neovascularization elsewhere (NVE) and neovascularization of the disc (NVD) were assessed. Perfusion was defined as arterial, arteriovenous, or venous if the area of diabetic neovascularization (NV) began to hyperfluoresce either prior, during, or after laminar venous flow, respectively. RESULTS: A total of 180 eyes from 176 patients with 928 NV were identified (830 NVE, 98 NVD). Of those, 5.1% of NVE were classified as arterial and 58.2% of NVD were classified as arterial. The remaining NV were classified as arteriovenous except for a small subset (6.1%) which were indeterminate. None of the NV were classified as venous. Noteworthy examples demonstrated NV that nearly fully perfused prior to any detectable fluorescence within nearby veins as well as clear shunting of blood from a feeding artery to a draining vein. CONCLUSIONS: UWF FA images suggest that some NV is perfused by retinal arteries. This may be useful in devising strategies for early detection and treatment of NV precursors. KEY MESSAGES: What is known • Diabetic retinal neovascularization has long been thought to be perfused by the retinal venous circulation. • Vascular endothelial growth factor has been shown to play key roles in both angiogenesis and arteriogenesis. What is new • Ultrawide-field fluorescein angiography demonstrates that at least some diabetic neovascularization is perfused by the retinal arterial circulation. • This supports the hypothesis that diabetic neovascularization may arise from arterially-perfused intraretinal microvascular abnormalities in the capillary bed.

The effect of mandatory post-call relief on sleep and wellness in ophthalmology residents.

BACKGROUND: Multiple duty hour reforms have been implemented to optimize resident wellness through increasing opportunities for sleep recovery, but few studies have recorded objectively measured sleep or shown direct sleep and wellness benefits from such interventions. This study seeks to determine whether mandatory post-call relief policies with a partial night float system improved resident sleep, activity, and burnout among ophthalmology residents taking home call. METHODS: We conducted a two group cohort study of ophthalmology residents at the University Washington comparing post graduate year-2 (PGY-2) resident sleep, activity, and burnout between the optional post-call relief group from July 1, 2017 to June 30, 2019 to the mandatory post-call relief group from July 1, 2019 to June 30, 2021. RESULTS: Of twenty total residents participating in the survey portion, 18 residents participated in the sleep and activity tracking portion of the study, 9 in in the optional post-call relief cohort, and 9 in the mandatory post-call relief cohort. The mandatory post-call relief group recorded longer total sleep on call than the optional post-call relief group (p < 0.001). There was no difference in overnight sleep recorded on call (median 3.4 h), but residents recorded more time napping in the mandatory post-call relief cohort (p < 0.001). There was no significant difference between cohorts in amount of sleep while not on call. Residents in the mandatory post-call relief cohort recorded higher average daily steps, higher exercise time, and lower sedentary time than residents in the optional post-call relief cohort (p < 0.001). They also recorded lower median emotional exhaustion on the Maslach Burnout Inventory and lower stress in the Depression and Anxiety Stress Scale in the mandatory post-call relief cohort (p = 0.008). CONCLUSIONS: Implementation of mandatory post-call relief policies with a partial night-float system among PGY-2 residents was associated with more post-call naps with more overall physical activity, lower emotional exhaustion scores, and lower stress scores, despite no changes to overnight sleep on call or total sleep. Although sample size limits interpretation of data, implementation of mandatory post call relief could be considered to improve post-call sleep in programs with home call.

Using Deep Learning to Automate Goldmann Applanation Tonometry Readings.

PURPOSE: To develop an objective and automated method for measuring intraocular pressure using deep learning and fixed-force Goldmann applanation tonometry (GAT) techniques. DESIGN: Prospective cross-sectional study. PARTICIPANTS: Patients from an academic glaucoma practice. METHODS: Intraocular pressure was estimated by analyzing videos recorded using a standard slit-lamp microscope and fixed-force GAT. Video frames were labeled to identify the outline of the reference tonometer and the applanation mires. A deep learning model was trained to localize and segment the tonometer and mires. Intraocular pressure values were calculated from the deep learning-predicted tonometer and mire diameters using the Imbert-Fick formula. A separate test set was collected prospectively in which standard and automated GAT measurements were collected in random order by 2 independent masked observers to assess the deep learning model as well as interobserver variability. MAIN OUTCOME MEASURES: Intraocular pressure measurements between standard and automated methods were compared. RESULTS: Two hundred sixty-three eyes of 135 patients were included in the training and validation videos. For the test set, 50 eyes from 25 participants were included. Each eye was measured by 2 observers, resulting in 100 videos. Within the test set, the mean difference between automated and standard GAT results was -0.9 mmHg (95% limits of agreement [LoA], -5.4 to 3.6 mmHg). Mean difference between the 2 observers using standard GAT was 0.09 mmHg (LoA,-3.8 to 4.0 mmHg). Mean difference between the 2 observers using automated GAT videos was -0.3 mmHg (LoA, -4.1 to 3.5 mmHg). The coefficients of repeatability for automated and standard GAT were 3.8 and 3.9 mmHg, respectively. The bias for even-numbered measurements was reduced when using automated GAT. CONCLUSIONS: Preliminary measurements using deep learning to automate GAT demonstrate results comparable with those of standard GAT. Automated GAT has the potential to improve on our current GAT measurement standards significantly by reducing bias and improving repeatability. In addition, ocular pulse amplitudes could be observed using this technique.

Characterisation and diagnosis of ulcers in inpatient dermatology consultation services: A multi-centre study.

Accurate and prompt diagnosis of skin ulcers is critical to optimise management; however, studies in hospitalised patients are limited. This retrospective review of dermatologic consultations included 272 inpatients with skin ulcers between July 2015 and July 2018 in four U.S. academic hospitals. The median age was 54 years and 45% were male. In 49.3% of the patients, skin ulcers were considered the primary reason for admission. Ulcers of 62% were chronic and 49.6% were located on the lower extremities. Pyoderma gangrenosum (17.3%), infection (12.5%), and exogenous causes (11.8%) were the leading aetiologies; 12% remained diagnostically inconclusive after consultation. Diagnostic agreements pre-dermatology and post-dermatology consult ranged from 0.104 (n = 77, 95% CI 0.051-0.194) to 0.553 (n = 76, 95% CI 0.440-0.659), indicating poor-modest agreement. This study highlights the diagnostic complexity and relative incidences of skin ulcers in the inpatient setting.

Combinational targeting offsets antigen escape and enhances effector functions of adoptively transferred T cells in glioblastoma.

Preclinical and early clinical studies have demonstrated that chimeric antigen receptor (CAR)-redirected T cells are highly promising in cancer therapy. We observed that targeting HER2 in a glioblastoma (GBM) cell line results in the emergence of HER2-null tumor cells that maintain the expression of nontargeted tumor-associated antigens. Combinational targeting of these tumor-associated antigens could therefore offset this escape mechanism. We studied the single-cell coexpression patterns of HER2, IL-13Rα2, and EphA2 in primary GBM samples using multicolor flow cytometry and immunofluorescence, and applied a binomial routine to the permutations of antigen expression and the related odds of complete tumor elimination. This mathematical model demonstrated that cotargeting HER2 and IL-13Rα2 could maximally expand the therapeutic reach of the T cell product in all primary tumors studied. Targeting a third antigen did not predict an added advantage in the tumor cohort studied. We therefore generated bispecific T cell products from healthy donors and from GBM patients by pooling T cells individually expressing HER2 and IL-13Rα2-specific CARs and by making individual T cells to coexpress both molecules. Both HER2/IL-13Rα2-bispecific T cell products offset antigen escape, producing enhanced effector activity in vitro immunoassays (against autologous glioma cells in the case of GBM patient products) and in an orthotopic xenogeneic murine model. Further, T cells coexpressing HER2 and IL-13Rα2-CARs exhibited accentuated yet antigen-dependent downstream signaling and a particularly enhanced antitumor activity.

Automated catheter segmentation and tip detection in cerebral angiography with topology-aware geometric deep learning.

BACKGROUND: Visual perception of catheters and guidewires on x-ray fluoroscopy is essential for neurointervention. Endovascular robots with teleoperation capabilities are being developed, but they cannot 'see' intravascular devices, which precludes artificial intelligence (AI) augmentation that could improve precision and autonomy. Deep learning has not been explored for neurointervention and prior works in cardiovascular scenarios are inadequate as they only segment device tips, while neurointervention requires segmentation of the entire structure due to coaxial devices. Therefore, this study develops an automatic and accurate image-based catheter segmentation method in cerebral angiography using deep learning. METHODS: Catheters and guidewires were manually annotated on 3831 fluoroscopy frames collected prospectively from 40 patients undergoing cerebral angiography. We proposed a topology-aware geometric deep learning method (TAG-DL) and compared it with the state-of-the-art deep learning segmentation models, UNet, nnUNet and TransUNet. All models were trained on frontal view sequences and tested on both frontal and lateral view sequences from unseen patients. Results were assessed with centerline Dice score and tip-distance error. RESULTS: The TAG-DL and nnUNet models outperformed TransUNet and UNet. The best performing model was nnUNet, achieving a mean centerline-Dice score of 0.98 ±0.01 and a median tip-distance error of 0.43 (IQR 0.88) mm. Incorporating digital subtraction masks, with or without contrast, significantly improved performance on unseen patients, further enabling exceptional performance on lateral view fluoroscopy despite not being trained on this view. CONCLUSIONS: These results are the first step towards AI augmentation for robotic neurointervention that could amplify the reach, productivity, and safety of a limited neurointerventional workforce.

Chronic subdural hematoma: What precisely are we treating?

Subdural hematoma (SDH) refers to the collection of blood between the dura matter and the arachnoid membrane. Advancements in imaging technology have enabled the categorization of SDH based on specific imaging characteristics, causative factors, and the onset of symptoms. Given that the prognosis of SDHs varies significantly and is contingent upon the size and chronicity of the hemorrhage, a comprehensive understanding of its subtypes may carry crucial treatment implications. For example, an acute SDH classically results from severe traumatic brain injury and appears as a homogenous, crescent-shaped hyperdense extra-axial collection. If not treated, over the course of 1-3 weeks, this hematoma will evolve into a sub-acute phenotype as a consequence of subdural effusion and demonstrate mixed-density hemorrhage on imaging. Chronic SDH (cSDH) becomes the end result of an untreated SDH, with neo-membranization and neo-angiogenesis from branches of the middle meningeal artery driving a mass-like growth pattern. This review article aims to elucidate the complex anatomical features of the end-stage cSDH, with a particular focus on reconceptualization of this entity based on its mass-like growth patterns, and how this is driving a shift towards endovascular treatment.

Direct superficial temporal artery access for middle meningeal artery embolization.

Middle meningeal artery embolization has become an important option in the management of subdural hemorrhages with multiple prospective studies demonstrating efficacy and randomized controlled trial data on the way. Access to the middle meningeal artery is usually achieved via the external carotid artery to the internal maxillary artery, then the middle meningeal artery. We report a case where a patient with symptomatic left-sided chronic subdural hemorrhage also had an external carotid artery occlusion. Direct puncture of the superficial temporal artery allowed retrograde access to the internal maxillary artery and thus the middle meningeal artery. Successful embolization of the vessel with 1:9 nBCA was performed with near total resorption of the subdural collection by 1 month postprocedure.

Current and future directions in interventional neuro-oncology-are we there yet?

Advancements in technology and technical expertise increasingly enable neurointerventionalists to deliver safer and more effective endovascular treatments to cancers of the brain, spine, head, and neck. In addition to established neuro-oncological interventions such as pre-surgical tumor embolization and percutaneous ablation, newer modalities focused on direct arterial infusion of chemotherapy, radioisotopes, and radiosensitizers continue to gain traction as complementary treatment options, while stem cell-mediated delivery of theranostic nanoparticles and oncolytic virus are being explored for even greater specificity in targeting cancers across the blood-brain barrier. This article aims to provide an overview of the current state of the art and future directions for the field of interventional neuro-oncology, as well as opportunities and challenges presented by this emerging treatment modality.

Multicenter early United States feasibility study and periprocedural safety of LVIS EVO for the treatment of unruptured intracranial aneurysms.

BACKGROUND: Stent development has focused recently on low-profile, self-expandable stents compatible with 0.0165 inch microcatheters. The LVIS EVO is the second-generation version of the Low-Profile Visualized Intraluminal Support (LVIS) with improved visibility and resheathability. The LVIS EVO underwent a limited premarket release (PMR) in December 2023. This study aims to report the early safety and feasibility experience with the LVIS EVO stent for the treatment of intracranial aneurysms in the United States (US). METHODS: This was a multicenter, retrospective, observational study evaluating patients who underwent treatment of an intracranial aneurysm with an LVIS EVO stent after the limited PMR. All physicians who had placed an LVIS EVO stent were asked to input their cases after institutional review board approval was obtained. The data were then sent to a single center for analysis. Any patient aged 18 years or older who underwent treatment of an intracranial aneurysm with a LVIS EVO stent in the US was included from the initial PMR in December 2023 until April 2024. Patient age (or ≤90 years old), sex, preoperative modified Rankin Scale (mRS), aneurysm location, aneurysm measurements, and information about preoperative antiplatelet management were all collected. Data on periprocedural complications, 30-day mortality, discharge mRS, and length of stay were also collected. RESULTS: Some 53 patients with 55 aneurysms underwent treatment with the LVIS EVO stent at 15 institutions. All aneurysms were unruptured. The most common location was the anterior communicating artery (35%) followed by the middle cerebral artery bifurcation (31%). All patients were on dual antiplatelet therapy. The average aneurysm size was 5.2 mm with a neck size of 3.7 mm. The smallest distal parent vessel size was 1.2 mm and 36% of stents were deployed in distal parent vessels <2 mm. All (100%) cases had successful deployment and the stent was repositioned in 10% of cases. A single stent was utilized in 91% of cases. Coils were placed in 48 cases (87.2%) and a microcatheter was jailed in 98% of those cases. Immediate Raymond Roy (RR) Class I occlusion was obtained in 33%, Class II in 22%, Class IIIa in 37%, and Class IIIb in 8% of cases. There were no delayed thromboembolic or hemorrhagic complications. CONCLUSIONS: The LVIS EVO is a braided, self-expanding, retrievable stent with enhanced visibility and smaller cell size. The drawn filled tube (DFT) technology results in improved visibility of the stent, allowing for more controlled stent positioning and visualization of vessel wall apposition. All cases in our series had complete neck coverage and good wall apposition. There were no thromboembolic or hemorrhagic complications.

Performance of Generative Large Language Models on Ophthalmology Board-Style Questions.

PURPOSE: To investigate the ability of generative artificial intelligence models to answer ophthalmology board-style questions. DESIGN: Experimental study. METHODS: This study evaluated 3 large language models (LLMs) with chat interfaces, Bing Chat (Microsoft) and ChatGPT 3.5 and 4.0 (OpenAI), using 250 questions from the Basic Science and Clinical Science Self-Assessment Program. Although ChatGPT is trained on information last updated in 2021, Bing Chat incorporates a more recently indexed internet search to generate its answers. Performance was compared with human respondents. Questions were categorized by complexity and patient care phase, and instances of information fabrication or nonlogical reasoning were documented. MAIN OUTCOME MEASURES: Primary outcome was response accuracy. Secondary outcomes were performance in question subcategories and hallucination frequency. RESULTS: Human respondents had an average accuracy of 72.2%. ChatGPT-3.5 scored the lowest (58.8%), whereas ChatGPT-4.0 (71.6%) and Bing Chat (71.2%) performed comparably. ChatGPT-4.0 excelled in workup-type questions (odds ratio [OR], 3.89, 95% CI, 1.19-14.73, P = .03) compared with diagnostic questions, but struggled with image interpretation (OR, 0.14, 95% CI, 0.05-0.33, P < .01) when compared with single-step reasoning questions. Against single-step questions, Bing Chat also faced difficulties with image interpretation (OR, 0.18, 95% CI, 0.08-0.44, P < .01) and multi-step reasoning (OR, 0.30, 95% CI, 0.11-0.84, P = .02). ChatGPT-3.5 had the highest rate of hallucinations and nonlogical reasoning (42.4%), followed by ChatGPT-4.0 (18.0%) and Bing Chat (25.6%). CONCLUSIONS: LLMs (particularly ChatGPT-4.0 and Bing Chat) can perform similarly with human respondents answering questions from the Basic Science and Clinical Science Self-Assessment Program. The frequency of hallucinations and nonlogical reasoning suggests room for improvement in the performance of conversational agents in the medical domain.

A rare case of solitary, isolated dural metastasis from hepatocellular carcinoma mimicking a meningioma.

Background: Distinguishing an isolated metastatic dural tumor from a meningioma on imaging is challenging and may lead to a delay in treatment. Here, we present the first known case of isolated, solitary dural metastasis from hepatocellular carcinoma (HCC) mimicking a meningioma. Case Description: A 64-year-old male with a history of liver cirrhosis presented with a 5.8 cm enhancing left parafalcine hemorrhagic dural-based mass extending across the midline. Cerebral angiography revealed a distal left anterior pseudoaneurysm, and tumor contrast blush with feeders from the left ophthalmic and right middle meningeal artery. The pseudoaneurysm was successfully embolized to stop the bleeding, followed by an uneventful bi-coronal frontal craniotomy for falcine tumor resection to relieve brain compression. Histopathological analysis of the dural-based tumor showed poorly differentiated carcinoma with positive albumin in situ hybridization and cytokeratin tumor markers, consistent with dural metastases from HCC. Conclusion: When encountering a solitary, highly vascular mass bearing resemblance to a meningioma, it may be prudent to consider the possibility of a dural-based metastatic carcinoma.

Topical adapalene for the treatment of follicular conjunctivitis due to periocular molluscum contagiosum in children.

PURPOSE: Periocular molluscum contagiosum can cause a chronic secondary follicular conjunctivitis or keratoconjunctivitis that rarely leads to corneal scarring and visual impairment. We describe two cases of follicular conjunctivitis due to periocular molluscum contagiosum that were successfully treated with topical adapalene 0.1%. OBSERVATIONS: Case 1 is a 9-year old female with a history of leg molluscum contagiosum who presented with three 1mm flesh-colored umbilicated papules on the periocular skin of the right eye with associated follicular conjunctivitis and diffuse corneal punctate epithelial erosions. Ocular symptoms were persistent for 6 months. Case 2 is a 4-year old female with a 3-month history of right periocular bumps and one month of conjunctival redness with eyelid edema. Examination revealed umbilicated flesh colored nodules on the right upper and lower eyelids with associated trace conjunctival injection. Both patients experienced rapid resolution of both eyelid involvement and conjunctivitis following the use of twice daily topical adapalene 0.1% to the eyelid lesions, with no reported side effects. CONCLUSIONS AND IMPORTANCE: Topical adapalene 0.1% is a cost-effective, convenient, and non-toxic over-the-counter retinoid cream that should be considered for first-line therapy in the treatment of periocular molluscum contagiosum and any associated conjunctivitis.

Pleural effusion and respiratory compromise from spontaneous migration of a ventriculoperitoneal shunt catheter in a patient with normal-pressure hydrocephalus.

Background: Ventriculoperitoneal shunt (VPS) insertion is one of the most common neurosurgical procedures done around the world to treat hydrocephalus. The occurrence of spontaneous migration of the peritoneal shunt catheter into the thoracic cavity is a very rare complication; we report here case number 27 of respiratory complications of a VPS in a patient with normal-pressure hydrocephalus (NPH). Case Description: A 76-year-old woman with Alzheimer's disease and anosognosia was diagnosed idiopathic NPH treated surgically with a VPS. Pleural effusion and pulmonary complications occurred 4 weeks after the insertion of the shunt due to the spontaneous migration of the peritoneal catheter of the VPS into the thoracic cavity. The hydrothorax of cerebrospinal fluid was drained and the distal catheter was removed and replaced. The patient made an uneventful recovery. Conclusion: Due to the rarity of this complication, there are no standard corrective procedures. Some of the methods used to diagnose and successfully treat this rare complication of the VPS are presented.

Desmoplastic non-infantile ganglioglioma in late adulthood.

Desmoplastic infantile ganglioglioma (DIG) is an uncommon supratentorial neuroepithelial brain tumor that typically occurs in infants younger than 24 months. Desmoplastic non-infantile ganglioglioma (DNIG) is a rare variant of this intracranial neoplasm. There are only 16 DNIG cases reported in the literature, with all patients under the age of 25 at the time of presentation. These DIG and DNIG cases were radiologically and histologically similar, with good outcome after treatment. Despite the size and high mitotic index for patients with DNIG, the prognosis is generally favorable and gross total resection is sufficient. We present a case of a 59-year-old woman with a DNIG. To the best of our knowledge, this is the first case reported of DNIG in late adulthood. Clinical presentation, histological and radiological findings are discussed.

The face value of feedback: facial behaviour is shaped by goals and punishments during interaction with dynamic faces.

Responding appropriately to others' facial expressions is key to successful social functioning. Despite the large body of work on face perception and spontaneous responses to static faces, little is known about responses to faces in dynamic, naturalistic situations, and no study has investigated how goal directed responses to faces are influenced by learning during dyadic interactions. To experimentally model such situations, we developed a novel method based on online integration of electromyography signals from the participants' face (corrugator supercilii and zygomaticus major) during facial expression exchange with dynamic faces displaying happy and angry facial expressions. Fifty-eight participants learned by trial-and-error to avoid receiving aversive stimulation by either reciprocate (congruently) or respond opposite (incongruently) to the expression of the target face. Our results validated our method, showing that participants learned to optimize their facial behaviour, and replicated earlier findings of faster and more accurate responses in congruent versus incongruent conditions. Moreover, participants performed better on trials when confronted with smiling, when compared with frowning, faces, suggesting it might be easier to adapt facial responses to positively associated expressions. Finally, we applied drift diffusion and reinforcement learning models to provide a mechanistic explanation for our findings which helped clarifying the underlying decision-making processes of our experimental manipulation. Our results introduce a new method to study learning and decision-making in facial expression exchange, in which there is a need to gradually adapt facial expression selection to both social and non-social reinforcements.

Relationships Between Sleep, Activity, and Burnout in Ophthalmology Residents.

OBJECTIVE: To objectively measure sleep and activity levels and examine their relationship to burnout, depression, anxiety, and stress in ophthalmology residents. DESIGN: A cohort study of ophthalmology residents at the University of Washington from July 1, 2017 to June 30, 2018. SETTING: Single-center academic institution. PARTICIPANTS: Fourteen ophthalmology residents at the University of Washington enrolled between July 1, 2017 and June 30, 2018. RESULTS: Data were collected from 14 residents, ages 27 to 34. Wrist actigraphy allowed for objective measurement of resident sleep and activity, though adherence to wrist actigraphy usage dropped significantly over time. Residents recorded significantly less sleep on call compared to when they were off call, with mean (SD) 3.6 (2.0) hours on primary call, 5.6 (1.8) hours on secondary call, and 6.7 (1.4) hours off call. Lower average sleep on call was associated with higher emotional exhaustion (r = -0.69, p = 0.04), lower personal accomplishment (r = 0.82, p = 0.007), higher anxiety (r = -0.90, p = 0.001), and higher stress (r = -0.75, p = 0.02). Higher daily activity was associated with higher sense of personal accomplishment (r = 0.57, p = 0.04). Average nightly sleep, average sleep while not on call, and daily sedentary time was not associated with any subset of burnout. CONCLUSIONS: The association between objectively measured sleep while on call and burnout, depression, and anxiety are consistent with findings from prior studies which relied on subjective measures of sleep. The direction of causality - whether poor sleep caused burnout, burnout caused poor sleep, or both - could not be assessed in the present study. However, these results are consistent with the hypothesis that poor sleep on call contributes to resident burnout and that physical activity may reduce aspects of burnout. The use of wrist actigraphy to objectively measure sleep and activity patterns may help focus and evaluate interventions aimed at decreasing resident burnout.