Nerve Capping Techniques for Neuroma Management: A Comprehensive Literature Review.

BACKGROUND/AIM OF THE STUDY: Nerve capping is a method of neuroma treatment or prevention that consists of the transplantation of a proximal nerve stump into an autograft or other material cap, after surgical removal of the neuroma or transection of the nerve. The aim was to reduce neuroma formation and symptoms by preventing neuronal adhesions and scar tissue. In this narrative literature review, we summarize the studies that have investigated the effectiveness of nerve capping for neuroma management to provide clarity and update the clinician's knowledge on the topic. METHODS: A systematic electronic search following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses criteria was performed in the PubMed database combining "neuroma," "nerve," "capping," "conduit," "treatment," "management," "wrap," "tube," and "surgery" as search terms. English-language clinical studies on humans and animals that described nerve capping as a treatment/prevention technique for neuromas were then selected based on a full-text article review. The data from the included studies were compiled based on the technique and material used for nerve capping, and technique and outcomes were reviewed. RESULTS: We found 10 applicable human studies from our literature search. Several capping materials were described: epineurium, nerve, muscle, collagen nerve conduit, Neurocap (synthetic copolymer of lactide and caprolactone, which is biocompatible and resorbable), silicone rubber, and collagen. Overall, 146 patients were treated in the clinical studies. After surgery, many patients were completely pain-free or had considerable improvement in pain scores, whereas some patients did not have improvement or were not satisfied after the procedure. Nerve capping was used in 18 preclinical animal studies, using a variety of capping materials including autologous tissues, silicone, and synthetic nanofibers. Preclinical studies demonstrated successful reduction in rates of neuroma formation. CONCLUSIONS: Nerve capping has undergone major advancements since its beginnings and is now a useful option for the treatment or prevention of neuromas. As knowledge of peripheral nerve injuries and neuroma prevention grows, the criterion standard neuroprotective material for enhancement of nerve regeneration can be identified and applied to produce reliable surgical outcomes.

Hormone physiology and sleep dynamics among BaYaka foragers of the Congo Basin: Gendered associations between nighttime activity, testosterone, and cortisol.

Sleep quality is an important contributor to health disparities and affects the physiological function of the immune and endocrine systems, shaping how resources are allocated to life history demands. Past work in industrial and post-industrial societies has shown that lower total sleep time (TST) or more disrupted nighttime sleep are linked to flatter diurnal slopes for cortisol and lower testosterone production. There has been little focus on these physiological links in other socio-ecological settings where routine sleep conditions and nighttime activity demands differ. We collected salivary hormone (testosterone, cortisol) and actigraphy-based sleep data from Congolese BaYaka foragers (N = 39), who have relatively short and fragmented nighttime sleep, on average, in part due to their typical social sleep conditions and nighttime activity. The hormone and sleep data collections were separated by an average of 11.23 days (testosterone) and 2.84 days (cortisol). We found gendered links between nighttime activity and adults' hormone profiles. Contrary to past findings in Euro-American contexts, BaYaka men who were more active at night, on average, had higher evening testosterone than those with lower nighttime activity, with a relatively flat slope relating nighttime activity and evening testosterone in women. Women had steeper diurnal cortisol curves with less disrupted sleep. Men had steeper cortisol diurnal curves if they were more active at night. BaYaka men often hunt and socialize when active at night, which may help explain these patterns. Overall, our findings indicate that the nature of nighttime activities, including their possible social and subsistence contexts, are potentially important modifiers of sleep quality-physiology links, meriting further research across contexts.

Risk factors and predictors of violence: insights from the emergency department at a level 1 trauma center in the USA.

BACKGROUND: This study aimed to assess the risk factors and predictors of violence among patients admitted to a Level 1 trauma center in a single institution. METHODS: We conducted a retrospective analysis of patients who were admitted with a history of violence between 2012 and 2016. RESULTS: A total of 9855 trauma patients were admitted, of whom 746 (7.6%) had a history of violence prior to the index admission. Patients who had history of violence were younger and more likely to be males, Black, Hispanic and covered by low-income primary payer in comparison to non-assault trauma patients (P < 0.001 for all). Multivariate logistic regression analysis showed that covariate-adjusted predictors of violence were being Black, male having low-income primary payer, Asian, drug user, alcohol intoxicated and smoker. CONCLUSIONS: Violence is a major problem among young age subjects with certain demographic, social and ethnic characteristics. Trauma centers should establish violence injury prevention programs for youth and diverse communities.

Complex Abdominal Wall Reconstruction with Biologic Mesh for Ventral/Umbilical Hernias in Patients with Cirrhosis: Technique and Outcomes.

INTRODUCTION: Patients with cirrhosis undergoing non-liver transplant surgery have a higher risk or adverse events than those without cirrhosis. The main objectives of this study were to describe characteristics, outcomes, and outcome predictors of cirrhotic patients undergoing complex abdominal wall reconstruction (CAWR) with biologic mesh. MATERIALS AND METHODS: This study had retrospective and prospective components, including all cirrhotic patients at our center with CAWR for ventral/umbilical hernia repair with biologic mesh between December 2016 and November 2021. RESULTS: We studied 37 patients with cirrhosis. Their mean age was 57.2 years, and 64.9% were male. The median body mass index (BMI) was 28.1kg/m2. Ascites was present in 83.3% of patients. The other most common comorbidities were alcohol abuse (67.6%), hypertension (37.8%), and diabetes (24.3%). All complications in aggregate occurred in 11 patients (29.7%). Six patients (16.2%) underwent reoperation. Surgical site infections (SSIs) occurred in five patients (13.5%). Four deaths occurred within 90 days (11.2% cumulative mortality). By 120 days, there were five deaths (14.2% mortality, but none due to the operation). Seven predictor variables achieved an area under the receiver operating characteristic curve (AUROC) for SSI of 0.963, and two predictors yielded an AUROC of 0.825 for 120-day mortality. CONCLUSIONS: Our results suggest that CAWR for ventral/umbilical hernias among cirrhotic patients is feasible given a dedicated CAWR team in collaboration with transplant surgeons and a transplant hepatologist. The rates of adverse outcomes were low or at the midpoint of the range of the study-specific estimates.

Neuroendocrine neoplasms of the gallbladder: early detection and surgery is key to improved outcome.

PURPOSE: Neuroendocrine neoplasms (NENs) of the gallbladder are very rare. As a result, the classification of pathologic specimens from gallbladder NENs, currently classified as gallbladder neuroendocrine tumors (GB-NETs) and carcinomas (GB-NECs), is inconsistent and makes nomenclature, classification, and management difficult. Our study aims to evaluate the epidemiological trend, tumor biology, and outcomes of GB-NET and GB-NEC over the last 5 decades. METHODS: This is a retrospective analysis of the SEER database from 1973 to 2016. The epidemiological trend was analyzed using the age-adjusted Joinpoint regression analysis. Survival was assessed with Kaplan-Meier analysis and Cox regression was used to assess predictors of poor survival. RESULTS: A total of 482 patients with GB-NEN were identified. Mean age at diagnosis was 65.2 ± 14.3 years. Females outnumbered males (65.6% vs. 34.4%). The Joinpoint nationwide trend analysis showed a 7% increase per year from 1973 to 2016. The mean survival time after diagnosis of GB-NEN was 37.11 ± 55.3 months. The most common pattern of nodal distribution was N0 (50.2%) followed by N1 (30.9%) and N2 (19.2%). Advanced tumor spread (into the liver, regional, and distant metastasis) was seen in 60.3% of patients. Patients who underwent surgery had a significant survival advantage (111.0 ± 8.3 vs. 8.3 ± 1.2 months, p < 0.01). Cox regression analysis showed advanced age (p < 0.01), tumor stage (P < 0.01), tumor extension (p < 0.01), and histopathologic grade (p < 0.01) were associated with higher mortality. CONCLUSION: Gallbladder NENs are a rare histopathological variant of gallbladder cancer that is showing a rising incidence in the USA. In addition to tumor staging, surgical resection significantly impacts patient survival, when patients are able to undergo surgery irrespective of tumor staging. Advanced age, tumor extension, and histopathological grade of the tumor were associated with higher mortality.

Biologic Mesh in Surgery: A Comprehensive Review and Meta-Analysis of Selected Outcomes in 51 Studies and 6079 Patients.

BACKGROUND: In recent decades, biologic mesh (BM) has become an important adjunct to surgical practice. Recent evidence-based clinical applications of BM include but are not limited to: reconstruction of abdominal wall defects; breast reconstruction; face, head and neck surgery; periodontal surgery; other hernia repairs (diaphragmatic, hiatal/paraesophageal, inguinal and perineal); hand surgery; and shoulder arthroplasty. Prior systematic reviews of BM in complex abdominal wall hernia repair had several shortcomings that our comprehensive review seeks to address, including exclusion of laparoscopic repair, assessment of risk of bias, use of an acceptable meta-analytic method and review of risk factors identified in multivariable regression analyses. MATERIALS AND METHODS: We sought articles of BM for open ventral hernia repair reporting on early complications, late complications or recurrences and included minimum of 50. We used the quality in prognostic studies risk of bias assessment tool. Random effects meta-analysis was applied. RESULTS: This comprehensive review selected 62 articles from 51 studies that included 6,079 patients. Meta-analytic pooling found that early complications are present in about 50%, surgical site occurrences (SSOs) in 37%, surgical site infections (SSIs) in 18%, reoperation in 7%, readmission in 20% and mortality in 3%. Meta-analytic estimates of late outcomes included overall complications (42%), SSOs (40%) and SSIs (22%). Specific SSOs included seroma (14%), hematoma (4%), abscess (10%), necrosis (5%), dehiscence (8%) and fistula formation (5%). Reoperation occurred in about 17%, mesh explantation in 9% and recurrence in 36%. CONCLUSION: Estimates of nearly all outcomes from individual studies were highly heterogeneous and sensitivity analyses and meta-regressions generally failed to explain this heterogeneity. Recurrence is the only outcome for which there are consistent findings for risk factors. Bridge placement of BM is associated with higher risk of recurrence. Prior hernia repair, history of reintervention and history of mesh removal were also risk factors for increased recurrence.

Taking the sleep lab to the field: Biometric techniques for quantifying sleep and circadian rhythms in humans.

OBJECTIVES: Remarkably, the specifics of sleep along the human lineage have been slow to emerge, which is surprising given our distinct mental and behavioral capacity and the importance of sleep for individual health and cognitive performance. Largely due to difficultly of measuring sleep outside a controlled, clinical, and laboratory study in ambulatory individuals, human biologists have yet to undergo a thorough examination of sleep in ecologically diverse settings. Here, I outline the procedures and methods for generating sleep data in a broader ecological context with the goal of facilitating the integration of sleep and circadian analyses into human biology research. METHODS: I describe the steps involved in participant recruitment, screening by way of survey instruments, and sample collection. In addition to describing field use of the traditional (but invasive) equipment such as the gold-standard application of electroencephalography (EEG), I demonstrate leading-edge noninvasive techniques for biometric devices (ie, wrist-worn actigraphy, ring worn arterial pulsometry) to generate sleep and circadian rhythms data. RESULTS: I outline best approaches to process and analyze data-including variables such as sleep duration, 24-hour sleep time (ie, summation of night and day sleep), sleep efficiency, sleep fragmentation, and nonparametric circadian rhythms analysis to quantify circadian amplitude. Finally, I discuss comparative statistical methods that are optimized for the use of time-series data. CONCLUSIONS: This review serves as an introduction to the best practices for studying sleep-wake patterns in humans-with the goal of standardizing tools for launching new human sleep biology research initiatives across the globe.

Independent Predictors for Surgical Site Infections in Patients Undergoing Complex Abdominal Wall Reconstruction.

INTRODUCTION: Complex abdominal wall reconstruction (CAWR) in patients with large abdominal defects have become a common procedure. The aim of this study was to identify independent predictors of surgical site infections (SSI) in patients undergoing CAWR. MATERIALS AND METHODS: This was an ambidirectional cohort study of 240 patients who underwent CAWR with biologic mesh between 2012 and 2020 at an academic tertiary/quaternary care center. Prior superficial SSI, deep SSI, organ space infections, enterocutaneous fistulae, and combined abdominal infections were defined as prior abdominal infections. Univariable and multivariable logistic regression models were performed to determine independent risk factors for SSI. RESULTS: There were a total of 39 wound infections, with an infection rate of 16.3%. Forty percent of patients who underwent CAWR in this study had a history of prior abdominal infections. In the multivariable regression models not weighted for length of stay (LOS), prior abdominal infection (odds ratio [OR]: 2.49, p=0.013) and higher body mass index (BMI) (OR: 1.05, p=0.023) were independent predictors of SSI. In the multivariable regression model weighted for LOS, prior abdominal infection (OR: 2.2, p=0.034), higher BMI (OR: 1.05, p=0.024), and LOS (OR: 1.04, p=0.043) were independent predictors of SSI. CONCLUSION: The history of prior abdominal infections, higher BMI, and increased LOS are important independent predictor of SSI following CAWR.

Early Abdominal Wall Reconstruction with Biologic Mesh is Feasible after Catastrophic Abdominal Wall Disruption from Blunt Trauma.

INTRODUCTION: Traumatic abdominal wall hernias (TAWHs) after blunt trauma, while rare, are typically associated with severe injuries, particularly those involved with the seatbelt triad of abdominal wall disruption. The aim of this study is to present a case series of patients with TAWHs that were managed at an early stage post injury with a biological mesh. MATERIALS AND METHODS: Patients with TAWH undergoing complex abdominal wall reconstruction (CAWR) between 2017 and 2020 were identified from our institutional database. All patients underwent definitive reconstruction using advanced surgical techniques including a posterior component separation with biological mesh (STRATTICE™, Allergan, Inc., Dublin, Ireland) placed in a sublay fashion. RESULTS: Seven patients underwent definitive TAWH repair during their index admission: the median age was 56 years (range 20-77) and the median Injury Severity Score (ISS) was 34 (29-50). The most common mechanism of injury was motor vehicle crash (MVC) at 86%, while the most common intra-abdominal concomitant injury was small bowel. Traumatic hernia location was on the right side of the abdominal wall in three patients, left in three patients, and bilaterally in one patient. There were no hernia recurrences or deaths in this small cohort. CONCLUSION: Traumatic abdominal wall disruption can be safely reconstructed using advanced surgical techniques with a biological mesh during the acute phase or same index hospitalization.

Falling Again? Falls in Geriatric Adults-Risk Factors and Outcomes Associated With Recidivism.

BACKGROUND: The elderly population is at increased risk of fall-related readmissions (FRRs). This study is aimed to identify the factors predictive of repeat falls and to analyze the associated outcomes. METHODS: We studied the Nationwide Readmission Database for the year 2010 and identified the patients (≥65 years) who were admitted after falls, and from that subset, further analyzed patients with ≥1 FRRs. Descriptive statistics were used to analyze continuous and categorical variables. Multivariable logistic regression was used to identify predictors of readmission in geriatric patients after controlling for covariates. RESULTS: A total of 358,581 initial fall-related admissions in geriatric adults were identified, and of these, 21,713 experienced ≥1 FRRs (6.06% risk of repeat fall-related admission). Females outnumbered males, and female gender was identified as an independent predictor of FRR (OR 1.10 95% CI 1.07-1.14 P = 0.000). The other independent predictors significantly associated with FRR were age (OR 1.007, 95% CI 1.005-1.009), depression (OR 1.25, 95% CI 1.21-1.30), drug abuse (OR 1.37, 95% CI 1.15-1.63), liver disease (OR 1.25, 95% CI 1.15-1.43, P < 0.001), psychosis (OR 1.16, 95% CI 1.09-1.23), valvular heart disease (OR 1.07, 95% CI 1.02-1.12), chronic pulmonary disease (OR 1.10, 95% CI 1.06-1.13), and number of chronic conditions (OR 1.022, 95% CI 1.016-1.29). Patients admitted emergently or urgently had higher odds of FRR (OR 1.44, 95% CI 1.36-1.52). Hospital demographic was a significant predictor of FRR, as hospitals with bed number >500 was associated with lower odds (OR 0.95, 95% CI 0.92-0.98, P < 0.001). Geriatric patients admitted at nonteaching hospitals and hospitals in large metro areas (population > 1 million) had higher odds of FRR (OR 1.10, 95% CI 1.03 - 1.16) and (OR 1.10, 95% C1 1.07-1.14), respectively. With respect to discharge disposition, patients in the FRR group were less likely to go home (5.9% versus 21.0%) or with home health care (12.6% versus 18.5%), but more likely to be discharged to skilled nursing or intermediate-care facilities (64.1% versus 54.9%) and short-term hospitals (2.8% versus 1.4%). The mortality rate was higher in the FRR group but was not statistically significant (OR 1.06, 95% CI 0.99-1.14). CONCLUSIONS: Given the high burden of fall-related injuries and FRRs to patients and the health care system, it is essential to identify those who are at risk. This study provides a comprehensive list of high-risk predictors as well as the impact on patient outcomes, and hence a chance to intervene for patients with FRRs.

Sex differences in daily activity intensity and energy expenditure and their relationship to cortisol among BaYaka foragers from the Congo Basin.

OBJECTIVES: The pooling of energetic resources and food sharing have been widely documented among hunter-gatherer societies. Much less is known about how the energetic costs of daily activities are distributed across individuals in such groups, including between women and men. Moreover, the metabolic physiological correlates of those activities and costs are relatively understudied. MATERIALS AND METHODS: Here, we tracked physical activity, energy expenditure (EE), and cortisol production among Congo Basin BaYaka foragers engaged in a variety of daily subsistence activities (n = 37). Given its role in energy mobilization, we measured overall daily cortisol production and short-term cortisol reactivity through saliva sampling; we measured physical activity levels and total EE via the wGT3X-bt actigraph and heart rate monitor. RESULTS: We found that there were no sex differences in likelihood of working in common activity locations (forest, garden, house). Across the day, women spent greater percentage time in moderate-to-vigorous physical activity (%MVPA) and had lower total EE than men. Females with higher EE (kCal/hr) produced greater cortisol throughout the day. Though not statistically significant, we also found that individuals with greater %MVPA had larger decreases in cortisol reactivity. DISCUSSION: BaYaka women sustained higher levels of physical activity but incurred lower energetic costs than men, even after factoring in sex differences in body composition. Our findings suggest that the distribution of physical activity demands and costs are relevant to discussions regarding how labor is divided and community energy budgets take shape in such settings.

Timing and Type of Bacteria In Surgical Site Infections Following Complex Abdominal Wall Reconstruction.

PURPOSE: The goal of this study was to assess the bacteriology of surgical site infections (SSIs) in patients undergoing complex abdominal wall reconstruction (CAWR) with biologic mesh. METHODS: This was a prospective cohort study of all patients who developed SSI following CAWR with biologic mesh between 2017-2020 at an academic tertiary/quaternary care center. The patients were subdivided into six overlapping groups: infections found during hospitalization vs. infections found after discharge, sensitive bacteria vs. resistant bacteria, and nosocomial bacteria vs. intestinal bacteria. RESULTS: Of the 194 patients who underwent CAWR during the study period, 33 (17%) developed SSI. SSI was more commonly discovered after discharge than during hospitalization. These SSIs were vancomycin-resistant Enterococcus (VRE) or methicillin-resistant Staphylococcus aureus (MRSA) rather than sensitive bacteria, and required re-operation, which were more frequently found following elective procedures. VRE and MRSA infections were more common with clean wounds than with clean/contaminated, contaminated, or dirty wounds, while SSIs with intestinal flora were more common following fistula and stoma takedown. CONCLUSIONS: Surgical site infections with resistant bacteria manifest more frequently post-discharge and require more re-admissions and re-operations.

Sleep influences cognitive performance in lemurs.

Primates spend almost half their lives asleep, yet little is known about how sleep influences their waking cognition. We hypothesized that diurnal and cathemeral lemurs differ in their need for consistent, non-segmented sleep for next-day cognitive function-including long-term memory consolidation, self-control, foraging efficiency, and sociality. Specifically, we expected that strictly diurnal Propithecus is more reliant on uninterrupted sleep for cognitive performance, as compared to four other lemur species that are more flexibly active (i.e., cathemeral). We experimentally inhibited sleep and tested next-day performance in 30 individuals of 5 lemur species over 960 total nights at the Duke Lemur Center in Durham, North Carolina. Each set of pair-housed lemurs experienced a sleep restriction and/or deprivation protocol and was subsequently tested in a variety of fitness-relevant cognitive tasks. Within-subject comparisons of performance on these tasks were made by switching the pair from the experimental sleep inhibited condition to a normal sleep environment, thus ensuring cognitive equivalency among individuals. We validated effectiveness of the protocol via actigraphy and infrared videography. Our results suggest that 'normal' non-disrupted sleep improved memory consolidation for all lemurs. Additionally, on nights of normal sleep, diurnal lemurs performed better in foraging efficiency tasks than cathemeral lemurs. Social behaviors changed in species-specific ways after exposure to experimental conditions, and self-control was not significantly linked with sleep condition. Based on these findings, the links between sleep, learning, and memory consolidation appear to be evolutionarily conserved in primates.

Sleep in a comparative context: Investigating how human sleep differs from sleep in other primates.

OBJECTIVES: Primates vary in their sleep durations and, remarkably, humans sleep the least per 24-hr period of the 30 primates that have been studied. Using phylogenetic methods that quantitatively situate human phenotypes within a broader primate comparative context, we investigated the evolution of human sleep architecture, focusing on: total sleep duration, rapid eye movement (REM) sleep duration, non-rapid eye movement (NREM) sleep duration, and proportion of sleep in REM. MATERIALS AND METHODS: We used two different Bayesian methods: phylogenetic prediction based on phylogenetic generalized least squares and a multistate Onrstein-Uhlenbeck (OU) evolutionary model of random drift and stabilizing selection. RESULTS: Phylogenetic prediction confirmed that humans sleep less than predicted for a primate of our body mass, predation risk, brain size, foraging needs, sexual selection, and diet. These analyses further revealed that humans pack an unexpectedly higher proportion of REM sleep within a shorter overall sleep duration, and do so by reducing NREM sleep (rather than increasing REM). The OU model generally confirmed these findings, with shifts along the human lineage inferred for TST, NREM, and proportion of REM, but not for REM. DISCUSSION: We propose that the risks and opportunity costs of sleep are responsible for shorter sleep durations in humans, with risks arising from terrestrial sleep involving threats from predators and conspecifics, and opportunity costs because time spent sleeping could be used for learning, creating material objects, and socializing.

The cost of deep sleep: Environmental influences on sleep regulation are greater for diurnal lemurs.

OBJECTIVES: Primates spend almost half their lives asleep, yet we know little about how evolution has shaped variation in the duration or intensity of sleep (i.e., sleep regulation) across primate species. Our objective was to test hypotheses related to how sleeping site security influences sleep intensity in different lemur species. METHODS: We used actigraphy and infrared videography to generate sleep measures in 100 individuals (males = 51, females = 49) of seven lemur species (genera: Eulemur, Lemur, Propithecus, and Varecia) at the Duke Lemur Center in Durham, NC. We also generated experimental data using sleep deprivation for 16 individuals. This experiment used a pair-wise design for two sets of paired lemurs from each genus, where the experimental pair experienced a sleep deprivation protocol while the control experienced normal sleeping conditions. We calculated a sleep depth composite metric from weighted z scores of three sleep intensity variables. RESULTS: We found that, relative to cathemeral lemurs, diurnal Propithecus was characterized by the deepest sleep and exhibited the most disruptions to normal sleep-wake regulation when sleep deprived. In contrast, Eulemur mongoz was characterized by significantly lighter sleep than Propithecus, and E. mongoz showed the fewest disruptions to normal sleep-wake regulation when sleep deprived. Security of the sleeping site led to greater sleep depth, with access to outdoor housing linked to lighter sleep in all lemurs that were studied. CONCLUSIONS: We propose that sleeping site security was an essential component of sleep regulation throughout primate evolution. This work suggests that sleeping site security may have been an important factor associated with the evolution of sleep in early and later hominins.

Chronotype variation drives night-time sentinel-like behaviour in hunter-gatherers.

Sleep is essential for survival, yet it also represents a time of extreme vulnerability to predation, hostile conspecifics and environmental dangers. To reduce the risks of sleeping, the sentinel hypothesis proposes that group-living animals share the task of vigilance during sleep, with some individuals sleeping while others are awake. To investigate sentinel-like behaviour in sleeping humans, we investigated activity patterns at night among Hadza hunter-gatherers of Tanzania. Using actigraphy, we discovered that all subjects were simultaneously scored as asleep for only 18 min in total over 20 days of observation, with a median of eight individuals awake throughout the night-time period; thus, one or more individuals was awake (or in light stages of sleep) during 99.8% of sampled epochs between when the first person went to sleep and the last person awoke. We show that this asynchrony in activity levels is produced by chronotype variation, and that chronotype covaries with age. Thus, asynchronous periods of wakefulness provide an opportunity for vigilance when sleeping in groups. We propose that throughout human evolution, sleeping groups composed of mixed age classes provided a form of vigilance. Chronotype variation and human sleep architecture (including nocturnal awakenings) in modern populations may therefore represent a legacy of natural selection acting in the past to reduce the dangers of sleep.

The evolution of human sleep: Technological and cultural innovation associated with sleep-wake regulation among Hadza hunter-gatherers.

Sleep is necessary for the survival of all mammalian life. In humans, recent investigations have generated critical data on the relationship between sleep and ecology in small-scale societies. Here, we report the technological and social strategies used to alter sleep environments and influence sleep duration and quality among a population of hunter-gatherers, the Hadza of Tanzania. Specifically, we investigated the effects that grass huts, sound levels, and fire had on sleep. We quantitatively compared thermal stress in outdoor environments to that found inside grass hut domiciles to test whether the huts function as thermoregulated microhabitats during the rainy season. Using physiological equivalent temperature (PET), we found that the grass huts provide sleep sites with less overall variation in thermal stress relative to outside baseline environments. We also investigated ambient acoustic measures of nighttime environments and found that sound significantly covaried with sleep-wake activity, with greater sound levels associating with less sleep. Finally, after controlling for ecological variables previously shown to influence sleep in this population, fire was shown to neither facilitate nor discourage sleep expression. Insofar as data among contemporary sub-tropical foragers can inform our understanding of past lifeways, we interpret our findings as suggesting that after the transition to full time terrestriality, it is likely that early Homo would have had novel opportunities to manipulate its environments in ways that could have significantly improved sleep quality. We further conclude that control over sleep environment would have been essential for migration to higher latitudes away from equatorial Africa.

Hadza sleep biology: Evidence for flexible sleep-wake patterns in hunter-gatherers.

OBJECTIVES: Cross-cultural sleep research is critical to deciphering whether modern sleep expression is the product of recent selective pressures, or an example of evolutionary mismatch to ancestral sleep ecology. We worked with the Hadza, an equatorial, hunter-gatherer community in Tanzania, to better understand ancestral sleep patterns and to test hypotheses related to sleep segmentation. METHODS: We used actigraphy to analyze sleep-wake patterns in thirty-three volunteers for a total of 393 days. Linear mixed effects modeling was performed to assess ecological predictors of sleep duration and quality. Additionally, functional linear modeling (FLM) was used to characterize 24-hr time averaged circadian patterns. RESULTS: Compared with post-industrialized western populations, the Hadza were characterized by shorter (6.25 hr), poorer quality sleep (sleep efficiency = 68.9%), yet had stronger circadian rhythms. Sleep duration time was negatively influenced by greater activity, age, light (lux) exposure, and moon phase, and positively influenced by increased day length and mean nighttime temperature. The average daily nap ratio (i.e., the proportion of days where a nap was present) was 0.54 (SE = 0.05), with an average nap duration of 47.5 min (SE = 2.71; n = 139). DISCUSSION: This study showed that circadian rhythms in small-scale foraging populations are more entrained to their ecological environments than Western populations. Additionally, Hadza sleep is characterized as flexible, with a consistent early morning sleep period yet reliance upon opportunistic daytime napping. We propose that plasticity in sleep-wake patterns has been a target of natural selection in human evolution.

Segmented sleep in a nonelectric, small-scale agricultural society in Madagascar.

OBJECTIVES: We studied sleep in a rural population in Madagascar to (i) characterize sleep in an equatorial small-scale agricultural population without electricity, (ii) assess whether sleep is linked to noise levels in a dense population, and (iii) examine the effects of experimentally introduced artificial light on sleep timing. METHODS: Using actigraphy, sleep-wake patterns were analyzed for both daytime napping and nighttime wakefulness in 21 participants for a sum total of 292 days. Functional linear modeling was used to characterize 24-h time-averaged circadian patterns and to investigate the effect of experimentally introduced mobile field lights on sleep timing. We also obtained the first polysomnography (PSG) recordings of sleep in a traditional population. RESULTS: In every measure of sleep duration and quality, the Malagasy population experienced shorter and lower quality sleep when compared to similarly measured postindustrial values. The population slept for a total of 6.5 h per night and napped during 89% of recorded days. We observed a peak in activity after midnight for both sexes on 49% of nights, consistent with segmented sleep. Access to mobile field lights had no statistical effect on nighttime sleep timing. From PSG, we documented relatively short rapid eye movement (14%), poor sleep efficiency (66%), and high wake after sleep onset (162 min). CONCLUSIONS: Sleep in this population is segmented, similar to the "first" sleep and "second" sleep reported in the historical record. Moreover, although average sleep duration and quality were lower than documented in Western populations, circadian rhythms were more stable across days.

Activity patterns in seven captive lemur species: Evidence of cathemerality in Varecia and Lemur catta?

Cathemerality, or activity throughout the 24-hr cycle, is rare in primates yet relatively common among lemurs. However, the diverse ecological conditions under which cathemerality is expressed complicates attempts to identify species-typical behavior. For example, Lemur catta and Varecia have historically been described as diurnal, yet recent studies suggest that they might exhibit cathemeral behavior under some conditions. To investigate this variation, we monitored activity patterns among lemurs that are exposed to similar captive environments. Using MotionWatch 8 ® actigraphy data loggers, we studied 88 lemurs across seven species at the Duke Lemur Center (DLC). Six species were members of the family Lemuridae (Eulemur coronatus, E. flavifrons, E. mongoz, L. catta, V. rubra, V. variegata), while a seventh was strictly diurnal and included as an out-group (Propithecus coquereli). For each 24-hr cycle (N = 503), we generated two estimates of cathemerality: mean night (MN) activity and day/night (DN) activity ratio (day and night cutoffs were based on astronomical twilights). As expected, P. coquereli engaged in the least amount of nocturnal activity according to both measures; their activity was also outside the 95% confidence intervals of all three cathemeral Eulemur species, which exhibited the greatest evidence of cathemerality. By these estimates, Varecia activity was most similar to Eulemur and exhibited substantial deviations from P. coquereli (ß (MN) = 0.22 ± SE 0.12; ß (DN) = -0.21 ± SE 0.12). L. catta activity patterns also deviated from P. coquereli (ß (MN) = 0.12 ± SE 0.11; ß (DN) = -0.15 ± SE 0.12) but to a lesser degree than either Varecia or Eulemur. Overall, L. catta displayed an intermediate activity pattern between Eulemur and P. coquereli, which is somewhat consistent with wild studies. Regarding Varecia, although additional observations in more diverse wild habitats are needed, our findings support the existence of cathemeral behavior in this genus.