Modeling Risk Factors for Intraindividual Variability: A Mixed-Effects Beta-Binomial Model Applied to Cognitive Function in Older People in the English Longitudinal Study of Ageing.

Cognitive functioning in older age profoundly impacts quality of life and health. While most research on cognition in older age has focused on mean levels, intraindividual variability (IIV) around this may have risk factors and outcomes independent of the mean value. Investigating risk factors associated with IIV has typically involved deriving a summary statistic for each person from residual error around a fitted mean. However, this ignores uncertainty in the estimates, prohibits exploring associations with time-varying factors, and is biased by floor/ceiling effects. To address this, we propose a mixed-effects location scale beta-binomial model for estimating average probability and IIV in a word recall test in the English Longitudinal Study of Ageing. After adjusting for mean performance, an analysis of 9,873 individuals across 7 (mean = 3.4) waves (2002-2015) found IIV to be greater at older ages, with lower education, in females, with more difficulties in activities of daily living, in later birth cohorts, and when interviewers recorded issues potentially affecting test performance. Our study introduces a novel method for identifying groups with greater IIV in bounded discrete outcomes. Our findings have implications for daily functioning and care, and further work is needed to identify the impact for future health outcomes.

Assessing mismatch negativity (MMN) and P3b within-individual sensitivity - A comparison between the local-global paradigm and two specialized oddball sequences.

Mismatch negativity (MMN) and P3b are well known for their clinical utility. There exists no gold standard, however, for acquiring them as EEG markers of consciousness in clinical settings. This may explain why the within-individual sensitivity of MMN/P3b paradigms is often quite poor and why seemingly identical EEG markers can behave differently across Disorders of consciousness (DoC) studies. Here, we compare two traditional paradigms for MMN or P3b assessment with the recently more popular local-global paradigm that promises to assess MMN and P3b orthogonally within one oddball sequence. All three paradigms were administered to healthy participants (N = 15) with concurrent EEG. A clear MMN and local effect were found for 15/15 participants. The P3b and global effect were found for 14/15 and 13/15 participants, respectively. There were no systematic differences between the global effect and P3b. Indeed, P3b amplitude was highly correlated across paradigms. The local effect differed clearly from the MMN, however. It occurred earlier than MMN and was followed by a much more prominent P3a. The peak latencies and amplitudes were also not correlated across paradigms. Caution should therefore be exercised when comparing the local effect and MMN across studies. We conclude that the within-individual MMN sensitivity is adequate for both the local-global and a dedicated MMN paradigm. The within-individual sensitivity of P3b was lower than expected for both the local-global and a dedicated P3b paradigm, which may explain the often-low sensitivity of P3b paradigms in patients with DoC.

Longitudinal blood glucose level and increased silent myocardial infarction: a pooled analysis of four cohort studies.

BACKGROUND: Fasting glucose (FG) demonstrates dynamic fluctuations over time and is associated with cardiovascular outcomes, yet current research is limited by small sample sizes and relies solely on baseline glycemic levels. Our research aims to investigate the longitudinal association between FG and silent myocardial infarction (SMI) and also delves into the nuanced aspect of dose response in a large pooled dataset of four cohort studies. METHODS: We analyzed data from 24,732 individuals from four prospective cohort studies who were free of myocardial infarction history at baseline. We calculated average FG and intra-individual FG variability (coefficient of variation), while SMI cases were identified using 12-lead ECG exams with the Minnesota codes and medical history. FG was measured for each subject during the study's follow-up period. We applied a Cox regression model with time-dependent variables to assess the association between FG and SMI with adjustment for age, gender, race, Study, smoking, longitudinal BMI, low-density lipoprotein level, blood pressure, and serum creatinine. RESULTS: The average mean age of the study population was 60.5 (sd: 10.3) years with median fasting glucose of 97.3 mg/dL at baseline. During an average of 9 years of follow-up, 357 SMI events were observed (incidence rate, 1.3 per 1000 person-years). The association between FG and SMI was linear and each 25 mg/dL increment in FG was associated with a 15% increase in the risk of SMI. This association remained significant after adjusting for the use of lipid-lowering medication, antihypertensive medication, antidiabetic medication, and insulin treatment (HR 1.08, 95% CI 1.01-1.16). Higher average FG (HR per 25 mg/dL increase: 1.17, 95% CI 1.08-1.26) and variability of FG (HR per 1 sd increase: 1.23, 95% CI 1.12-1.34) over visits were also correlated with increased SMI risk. CONCLUSIONS: Higher longitudinal FG and larger intra-individual variability in FG over time were associated in a dose-response manner with a higher SMI risk. These findings support the significance of routine cardiac screening for subjects with elevated FG, with and without diabetes.

Intra-individual variability of serum progesterone levels on the day of frozen blastocyst transfer in hormonal replacement therapy cycles.

STUDY QUESTION: Is there a significant intra-individual variability of serum progesterone levels on the day of single blastocyst Hormone Replacement Therapy-Frozen Embryo Transfer (HRT-FET) between two consecutive cycles? SUMMARY ANSWER: No significant intra-individual variability of serum progesterone (P) levels was noted between two consecutive HRT-FET cycles. WHAT IS KNOWN ALREADY: In HRT-FET cycles, a minimum P level on the day of embryo transfer is necessary to optimise reproductive outcomes. In a previous study by our team, a threshold of 9.8 ng/ml serum P was identified as significantly associated with the live birth rates in single autologous blastocyst transfers under HRT using micronized vaginal progesterone (MVP). Such patients may benefit from an intensive luteal phase support (LPS) using other routes of P administration in addition to MVP. A crucial question in the way towards individualising LPS is whether serum P measurements are reproducible for a given patient in consecutive HRT-FET cycles, using the same LPS. STUDY DESIGN, SIZE, DURATION: We conducted an observational cohort study at the university-based reproductive medicine centre of our institution focusing on women who underwent at least two consecutive single autologous blastocyst HRT-FET cycles between January 2019 and March 2020. PARTICIPANTS/MATERIALS, SETTING, METHODS: Patients undergoing two consecutive single autologous blastocyst HRT-FET cycles using exogenous oestradiol and vaginal micronized progesterone for endometrial preparation were included. Serum progesterone levels were measured on the morning of the Frozen Embryo Transfer (FET), by a single laboratory. The two measurements of progesterone levels performed on the day of the first (FET1) and the second FET (FET2) were compared to evaluate the intra-individual variability of serum P levels. Paired statistical analyses were performed, as appropriate. MAIN RESULTS AND THE ROLE OF CHANCE: Two hundred and sixty-four patients undergoing two consecutive single autologous blastocyst HRT-FET were included. The mean age of the included women was 35.0 ± 4.2 years. No significant intra-individual variability was observed between FET1 and FET2 (mean progesterone level after FET1: 13.4 ± 5.1 ng/ml vs after FET2: 13.9 ± 5.0; P = 0.08). The characteristics of the embryo transfers were similar between the first and the second FET. Forty-nine patients (18.6%) had discordant progesterone levels (defined as one progesterone measurement > and one ≤ to the threshold of 9.8 ng/ml) between FET1 and FET2. There were 37/264 women (14.0%) who had high intra-individual variability (defined as a difference in serum progesterone values >75th percentile (6.0 ng/ml)) between FET1 and FET2. No specific clinical parameter was associated with a high intra-individual variability nor a discordant P measurement. LIMITATIONS, REASONS FOR CAUTION: This study is limited by its retrospective design. Moreover, only women undergoing autologous blastocyst HRT-FET with MVP were included, thereby limiting the extrapolation of the study findings to other routes of P administration and other kinds of endometrial preparation for FET. WIDER IMPLICATIONS OF THE FINDINGS: No significant intra-individual variability was noted. The serum progesterone level appeared to be reproducible in >80% of cases. These findings suggest that the serum progesterone level measured on the day of the first transfer can be used to individualize luteal phase support in subsequent cycles. STUDY FUNDING/COMPETING INTEREST(S): No funding or competing interests. TRIAL REGISTRATION NUMBER: N/A.

The Gender-Equality Paradox in Intraindividual Academic Strengths: A Cross-Temporal Analysis.

Independent of overall achievement, girls' intraindividual academic strength is typically reading, whereas boys' strength is typically mathematics or science. Sex differences in intraindividual strengths are associated with educational and occupational sex disparities in science, technology, engineering, and mathematics (STEM) fields. Paradoxically, these sex differences are larger in more gender-equal countries, but the stability of this paradox is debated. We assessed the stability of the gender-equality paradox in intraindividual strengths, and its relation to wealth, by analyzing the academic achievement of nearly 2.5 million adolescents across 85 countries and regions in five waves (from 2006 to 2018) of the Programme for International Student Assessment (PISA). Girls' intraindividual strength in reading and boys' strength in mathematics and science were stable across countries and waves. Boys' advantage in science as an intraindividual strength was larger in more gender-equal countries, whereas girls' advantage in reading was larger in wealthier countries. The results have implications for reducing sex disparities in STEM fields.

Modeling intra-individual inter-trial EEG response variability in autism.

Autism spectrum disorder (autism) is a prevalent neurodevelopmental condition characterized by early emerging impairments in social behavior and communication. EEG represents a powerful and non-invasive tool for examining functional brain differences in autism. Recent EEG evidence suggests that greater intra-individual trial-to-trial variability across EEG responses in stimulus-related tasks may characterize brain differences in autism. Traditional analysis of EEG data largely focuses on mean trends of the trial-averaged data, where trial-level analysis is rarely performed due to low neural signal to noise ratio. We propose to use nonlinear (shape-invariant) mixed effects (NLME) models to study intra-individual inter-trial EEG response variability using trial-level EEG data. By providing more precise metrics of response variability, this approach could enrich our understanding of neural disparities in autism and potentially aid the identification of objective markers. The proposed multilevel NLME models quantify variability in the signal's interpretable and widely recognized features (e.g., latency and amplitude) while also regularizing estimation based on noisy trial-level data. Even though NLME models have been studied for more than three decades, existing methods cannot scale up to large data sets. We propose computationally feasible estimation and inference methods via the use of a novel minorization-maximization (MM) algorithm. Extensive simulations are conducted to show the efficacy of the proposed procedures. Applications to data from a large national consortium find that children with autism have larger intra-individual inter-trial variability in P1 latency in a visual evoked potential (VEP) task, compared to their neurotypical peers.

Adiposity influences intraindividual variability in behavioral and neuroelectric indices of attentional inhibition.

While overweight or obesity are thought to affect over 70% of the US population, the effects of adiposity on neurocognitive efficiency and stability remain unclear. Intra-individual variability or trial-to-trial variability (IIV) could provide insights into the influence of adiposity on neurophysiological stability. However, previous work examining the association between adiposity and IIV of cognitive outcomes is limited. Thus, this study examined the association between whole-body fat (%BF) and central tendency and IIV metrics of behavioral performance and event-related potentials. Adults (n = 320; 19-64 yrs) completed the Flanker task to assess attentional inhibition with concurrent electroencephalogram recordings to examine the N2 and P3b components. In addition to central tendency outcomes typically reported (i.e., mean accuracy and reaction time [RT]), dispersion outcomes (e.g., standard deviation [SD] of RT, P3b latency, N2 latency, etc.) were also extracted. Upon controlling for age and sex, %BF was inversely associated with (congruent: ß = -.18, p = .016; incongruent: ß = -.23, p < .001) accuracy. Increasing %BF was related to greater RT SD (congruent: ß = .13, p = .032; incongruent: ß = .23, p < .001). Furthermore, increased %BF was associated with slower P3b latencies (congruent: ß = .21, p = .003; incongruent: ß = .18, p = .010), and greater incongruent N2 (ß = .16, p = .017) and P3b (ß = .16, p = .025) latency SD. These findings suggest adiposity exerts a generalized negative influence on attentional inhibition for both measures of central tendency and dispersion across behavioral and neuroelectric indices.

A registered report of a two-site study of variations of the flanker task: ERN experimental effects and data quality.

Error-related negativity is a widely used measure of error monitoring, and many projects are independently moving ERN recorded during a flanker task toward standardization, optimization, and eventual clinical application. However, each project uses a different version of the flanker task and tacitly assumes ERN is functionally equivalent across each version. The routine neglect of a rigorous test of this assumption undermines efforts to integrate ERN findings across tasks, optimize and standardize ERN assessment, and widely apply ERN in clinical trials. The purpose of this registered report was to determine whether ERN shows similar experimental effects (correct vs. error trials) and data quality (intraindividual variability) during three commonly used versions of a flanker task. ERN was recorded from 172 participants during three versions of a flanker task across two study sites. ERN scores showed numerical differences between tasks, raising questions about the comparability of ERN findings across studies and tasks. Although ERN scores from all three versions of the flanker task yielded high data quality and internal consistency, one version did outperform the other two in terms of the size of experimental effects and the data quality. Exploratory analyses of the error positivity (Pe) provided tentative support for the other two versions of the task over the paradigm that appeared optimal for ERN. The present study provides a roadmap for how to statistically compare psychometric characteristics of ERP scores across paradigms and gives preliminary recommendations for flanker tasks to use for ERN- and Pe-focused studies.

The interplay of dopaminergic genotype and parent-child relationship in relation to intra-individual response time variability in preschoolers: A replication study.

Intra-individual response time variability (IIRTV) during cognitive performance is increasingly recognized as an important indicator of attentional control (AC) and related brain region function. However, what determinants contribute to preschoolers' IIRTV received little attention. The present study explored the interaction of dopaminergic polygenic composite score (DPCS) and the parent-child relationship in relation to preschoolers' IIRTV. In the initial sample, 452 preschoolers (M age = 5.17, SD = 0.92) participated in the study. The modified Flanker task was used to evaluate children's IIRTV and their parents were requested to complete the Parent-Child Relationship Scale to assess the parent-child relationship (closeness/conflict). DNA data were extracted from children's saliva samples, and a DPCS was created by the number of COMT, DAT1, and DRD2 alleles associated with lower dopamine levels. Results showed that DPCS significantly interacted with the parent-child closeness to impact preschoolers' IIRTV. Specifically, preschoolers with higher DPCS exhibited lower IIRTV under higher levels of the parent-child closeness, and greater IIRTV under lower levels of the parent-child closeness compared to those with lower DPCS, which supported the differential susceptibility theory (DST). A direct replication attempt with 280 preschoolers (M age = 4.80, SD = 0.86) was conducted to investigate whether the results were in accordance with our exploratory outcomes. The interactive effect of DPCS and the parent-child closeness on IIRTV was confirmed. Additionally, the significant interactive effect of DPCS and the parent-child conflict on IIRTV was found in the replication study. The findings indicate that preschoolers' IIRTV, as an indicator of AC and related brain region function, is influenced by the interactions of dopaminergic genotypes and the parent-child relationship. RESEARCH HIGHLIGHTS: We investigated the Gene × Environment mechanism to underline the intra-individual response time variability as an indicator of attentional control (AC) in Chinese preschoolers. Dopaminergic polygenic composite score (COMT, DAT1, and DRD2) interacted with the parent-child relationship to predict preschoolers' intra-individual reaction time variability. A direct replication attempt has been conducted, and the results were in accordance with our exploratory outcomes, which increased the credibility of the present findings. The findings highlight the importance of considering precursors, including polygenic and environmental factors, which contribute to the development of early cognitive performance such as AC.

Revisiting unstable disability and the fluctuations of frailty: a measurement burst approach.

BACKGROUND: It has been hypothesised that frailty is the root cause of clinically observed but rarely systematically measured unstable disability among older adults. In this study, we measure the extent of short-term disability fluctuations and estimate their association with frailty using intensive longitudinal data. METHODS: Repeated measurements of disability were collected under a measurement burst design in the FRequent health Assessment In Later life (FRAIL70+) study. A total of 426 community-dwelling older adults (70+) in Austria were interviewed about difficulties with basic, instrumental and mobility-related activities of daily living biweekly up to a total of 14 times in two measurement bursts (2891 and 2192 observations). Baseline frailty was assessed with both physical frailty (FP) and the frailty index (FI). Disability fluctuations were measured with the intra-individual interquartile range (iIQR) and estimated with a two-step generalised mixed regression procedure. RESULTS: Fewer participants were frail at baseline according to FP (11%) than FI (32%). Frail study participants reported not only more severe disability but also had more short-term disability fluctuations (iIQR = 1.0-1.5) compared with their robust counterparts (iIQR = 0). Regression models indicated that baseline frailty was associated with 2-3 times larger short-term disability fluctuations, which were also more prevalent among women, and increased with age and disability severity. CONCLUSION: Compared with those who were robust, frail older adults were characterised by not only more severe but also more unstable disability. Short-term disability fluctuations are closely tied to disability severity. Future studies should assess both stressors that may cause disability fluctuations among frail older adults as well as their potential consequences to inform frailty-centred care.

The ups and downs of self-criticism and disordered eating: Complementing Paranjothy and Wade's (2024) analysis by considering both trait and state perspectives.

Paranjothy and Wade's (2024) meta-review reveals that individuals higher in the personality trait of self-criticism consistently experience more disordered eating than those lower in the trait. The clinical implications of this meta-review are important in that they suggest current theoretical models and clinical practices in the field of eating disorders should incorporate a greater focus on self-criticism. Building on this exciting contribution, we highlight conceptual, practical, and empirical reasons why the field would benefit from supplementing this research on trait self-criticism with investigations of state self-criticism. We review research showing that self-criticism levels vary not only between individuals, with some people chronically more self-critical than others, but also within a person, with a given individual enacting relatively more self-criticism during some moments and days than others. We then present emerging research showing that these periods of higher-than-usual self-criticism are associated with more disordered eating. Thus, we emphasize the need to explore the factors that give rise to self-critical states in daily life, and review preliminary findings on this topic. We highlight the ways in which research on within-person variations in self-criticism can complement research on trait self-criticism to advance case formulation, prevention, and treatment in the field of eating disorders.

'With or without you': associations between noteworthy events and cognitive complaints across 100 days.

OBJECTIVES: Daily noteworthy events have implications for physical and mental health, but less is known about the role daily events have for self-reported cognition and whether the involvement of close social partners differentiates these associations. The current study examined how daily positive and negative noteworthy events relate to subjective memory and attentional difficulties and whether close social partners moderated associations. METHOD: We used data from a 100-day microlongitudinal web-based study of 104 older adults (Nobservations=7,051; Mage=63.13 years, SDage=7.81, 88.46% Female). Participants reported on exposure to and valence of noteworthy events, involvement of close social partners, and subjective cognitive complaints at the end of each day. RESULTS: Logistic multilevel models revealed that days with a negative event were associated with increased odds of forgetting something and trouble concentrating whereas days with positive events were associated with decreased odds of trouble concentrating. Close social partner involvement did not moderate within-person associations. CONCLUSION: Our results suggest that day-to-day events are correlates of cognitive complaints regardless of close social partner involvement in the events. Research should clarify the role of daily positive and negative events in personalized interventions and determine whether this person-centered approach to self-reported cognitive health helps inform diagnostic practices.

Aggressive behaviors predict greater intraindividual reaction time variability in children: Evidence from cross-lagged panel models.

Deficits in attentional control or inhibitory control are distinct features of childhood aggressive behaviors. Lower attentional control or inhibitory control is considered to predict more aggressive behaviors, while few studies have documented the possible predictive effects of aggressive behaviors on attentional control or inhibitory control. The present study examined the bidirectional relations between aggressive behaviors and both inhibitory control and attentional control in 169 Chinese primary school children (75 girls, Mage = 7.15, SDage = 0.33), annually for 3 years starting at age 7. The No-go accuracy on a Go/No-go task was used as the index of inhibitory control, and the intraindividual reaction time variability (IIRTV) of correct Go trials indicated attentional control. The aggressive behaviors subscale of the child behavior checklist-Chinese version was used to assess the children's aggressive behaviors. The results demonstrated a significant and stable predictive effect of previous aggressive behaviors on subsequent attentional control, with more aggressive behaviors predicting greater IIRTV at both the between-child and within-child levels. No significant effects of inhibitory control or attentional control on aggressive behaviors or sex-specific patterns were found. The findings suggest the negative impact of childhood aggressive behaviors on attentional control and underscore the importance of early prevention and intervention for childhood aggressive behaviors.

Integrating Intra- and Interindividual Phenomena in Psychological Theories.

Psychological science is divided into two distinct methodological traditions. One tradition seeks to understand how people function at the individual level, while the other seeks to understand how people differ from each other. Methodologies that have grown out of these traditions typically rely on different sources of data. While both use statistical models to understand the structure of the data, and these models are often similar, Molenaar (2004) showed that results from one type of analysis rarely transfer to the other, unless unrealistic assumptions hold. This raises the question how we may integrate these approaches. In this paper, we argue that formalized theories can be used to connect intra- and interindividual levels of analysis. This connection is indirect, in the sense that the relationship between theory and data is best understood through the intermediate level of phenomena: robust statistical patterns in empirical data. To illustrate this, we introduce a distinction between intra- and interindividual phenomena, and argue that many psychological theories will have implications for both types of phenomena. Formalization provides us with a methodological tool for investigating what kinds of intra- and interindividual phenomena we should expect to find if the theory under consideration were true.

Intraindividual Variability in Attention-Deficit/Hyperactivity Disorder: An Ex-Gaussian Approach.

Higher intraindividual variability (IIV) of response times is consistently noted in children with attention-deficit/hyperactivity disorder (ADHD). The current study investigated whether an ex-Gaussian estimate of IIV in children ages 6-13 years-old could differentiate between children with and without ADHD. Children completed a computerized go/no-go task to estimate trial-by-trial IIV and a continuous performance test (CPT) to estimate inattention and hyperactivity/impulsivity. Parents completed questionnaires assessing inattention and hyperactive/impulsive behaviors. IIV, commission errors, and attention problems as rated by parents were significantly greater in the ADHD group. Groups did not differ on errors of omission, but IIV was predictive of omission errors and parent ratings of inattention and hyperactivity/impulsivity. IIV predicted group membership (ADHD vs Control) whereas errors of omission did not. However, IIV did not improve diagnostic accuracy when parent ratings were used, such that parent ratings were superior at determining diagnosis. Current results support the use of IIV, based on the ex-Gaussian approach, as an objective measure of attention problems over omission errors on sustained attention CPT-type tasks. Additionally, while parent ratings of attention impairment remain the best predictor of ADHD diagnostic status, IIV may be helpful in determining when further assessment is required in the absence of those ratings.

The Role of Self-Esteem in Protecting Against Cyber-Victimization and Gaming Disorder Symptoms Among Adolescents: A Temporal Dynamics Analysis.

Previous literature has suggested that victimization is linked to low self-esteem and increases the symptoms of gaming disorder. However, little is known about the intra-individual processes, and the temporal dynamics of cyber-victimization, self-esteem, and gaming disorder symptoms. To address this gap, a three-year longitudinal study was performed using data collected at six different time points from 4206 Chinese adolescents (aged 12-17 years; 50.4% boys). Results of random intercept cross-lagged panel models (RI-CLPMs) indicated that at the within-person level, the fluctuation in self-esteem weakly predicted late cyber-victimization, and the fluctuation of cyber-victimization also weakly predicted late self-esteem. Additionally, the current study identified an interactive effect between self-esteem and gaming disorder symptoms at the within-person level. Fluctuations in self-esteem negatively predicted late gaming disorder symptoms, and vice versa. However, when combining the three variables (i.e., cyber-victimization, self-esteem, and gaming disorder symptoms) into one RI-CLPM, the results did not support the mediation of self-esteem in the relationship between cyber-victimization and gaming disorder symptoms at the within-person level. Moreover, fluctuations in self-esteem negatively predicted late gaming disorder symptoms and cyber-victimization at the within-person level in the RI-CLPM. These findings emphasize the protective role of self-esteem developed against cyber-victimization and gaming disorder symptoms among adolescents.

Predicting Intraindividual Change in Satisfaction with Life During COVID-19: A Prospective Study of Swiss Older Adults with Differing Levels of Childhood Adversity.

Objectives This study examined intraindividual change in satisfaction with life (SWL) in Swiss older adults before, during, and after COVID-19. It assessed whether predictors of adaptation influenced SWL stability, and whether this differed depending on adverse childhood experiences (ACE). Methods SWL was assessed eight times over a 21-month period. ACE, emotion regulation, meaning in life, and subjective socio-economic status (SES) were assessed as predictors. Data were analyzed using growth curve modeling. Results The sample consisted of two groups: A risk group (RG: n = 111, M age = 69.4 years) comprised of individuals with a high risk of having been exposed to ACE, and a (low-risk) control group (CG: n = 120, M age = 70.3 years). Intraindividual change in SWL was predicted by (presence of) meaning in life only in the RG, and by subjective SES only in the CG. Conclusion Results identified predictors of stable SWL trajectories and the potential for positive psychological functioning into later life, despite past and current prolonged adversity. Supplementary Information: The online version contains supplementary material available at 10.1007/s10902-024-00791-2.

Cognitive impairment after sleep deprivation: The role of precuneus related connectivity on the intra-individual variability changes.

OBJECTIVE: Intra-individual variability (IIV) in cognitive performance is thought to reflect the efficiency with which attentional resources are allocated in different circumstances requiring cognitive control. IIV in cognitive performance is associated with the strength of the negative correlation between task-positive network and default mode network (DMN) activity. In this study, we investigated the impact of sleep deprivation (SD) on functional connectivity (FC) between the DMN and psychomotor vigilance task-related network (PVT-RN), and its relationship with IIV in cognitive performance. METHODS: Two analyses, network-level independent component analysis (NL-ICA) and region-level (RL)-ICA, were employed to compare the coefficient of variation (CV) of the PVT between normal sleep and SD conditions across 67 healthy participants. RESULTS: After SD, in NL-ICA, the FC between the PVT-RN and DMN was positively correlated with the CV of the PVT, as well as the changes therein, compared with normal sleep. Using a mask derived from the DMN and PVT-RN, the RL-ICA revealed that 12 edges/connections between DMN and PVT independent components were associated with the CV of the PVT, with nine of these connections involving the precuneus. CONCLUSIONS: These findings suggest that the precuneus may play a crucial role in the interactions of various brain functions during the PVT, with the connections between the precuneus and frontoparietal and somatosensory networks being significantly altered after SD. Moreover, following SD, weakened negative FC between the precuneus and bilateral inferior parietal lobule may disrupt the balance between cognitive and executive control functions, leading to a decline in cognitive performance.

Biological variation in thyroid function tests in older adults and clinical implications.

OBJECTIVE: Interpreting thyroid function tests can be challenging due to inherent variation, and the need for tests rises with age. While age-related changes in thyrotropin (TSH) levels are known, the biological variation in older adults remains unclear. DESIGN: We recruited nineteen 65-99-year-old (older adults) without thyroid disease for monthly blood sampling for 1 year. PATIENTS AND MEASUREMENTS: Serum was stored at -20C°, and TSH, total thyroxine (TT4) and total triiodothyronine (TT3) were analysed in random order in a single batch for each participant. Results were compared to test results from 15 euthyroid men aged 24-53 years (younger adults) collected previously using a similar methodology. RESULTS: Interindividual coefficients of variation in older/younger adults were 46.7%/44.0% for TSH, 12.7%/19.5% for TT4 and 14.6%/22.4% for TT3. Intraindividual coefficients of variation (CVI ) were 19.0%/25.4% for TSH, 5.5%/10.8% for TT4 and 6.9%/13.2% for TT3. The index of individuality was below 0.6 for all hormones in all age groups. The number of samples required to determine the homoeostatic set-point at 10% precision in older adults was 14-21 for TSH and 2 for TT4 and TT3. TT4 in older adults was the only parameter in any group with comparable CVI between individuals (p = .22). CONCLUSIONS: CVI for TT4 and TT3 was halved in older compared to younger adults with two tests of TT4 needed to describe the individual set-point. Similar CVI between older adults caused TT4 to provide a reliable estimate of thyroid function, and the added value of measuring thyroxine could improve clinical practice.

Sleep regularity in healthy adolescents: Associations with sleep duration, sleep quality, and mental health.

Current evidence points to the importance of sleep for adolescent physical and mental health. To date, most studies have examined the association between sleep duration/quality and health in adolescence. An emerging line of research suggests that regularity in the timing of sleep may also play an important role in well-being. To address this aspect of sleep, the present study investigated daily variability of sleep, quantified using the sleep regularity index (SRI), in 46 adolescents (M = 12.78 ± 1.07 years) and its association with depressive symptoms/mental health. Sleep was measured during a 6 month period (M = 133.11 ± 36.42 nights) using actigraphs to quantify SRI values calculated for school days, weekends and holidays. Depressive symptoms and general psychopathology were assessed at the beginning (baseline) and end (follow-up) of the actigraphy measurements. Sleep was most regular during school days and associated with a longer total sleep time, shorter sleep onset latency, and higher sleep efficiency. Moreover, a higher SRI on school days was associated with fewer depressive symptoms at follow-up, whereas higher SRI on weekends was associated with less overall psychopathology at follow-up. Furthermore, the change in overall psychopathology, but not depressive symptoms across the two assessments was correlated with sleep regularity index. Our results suggest that regular timing of sleep is associated with sleep that is of longer duration and higher quality and may be protective of adolescent mental health. Therefore, adolescents should be encouraged not only to get enough sleep, but also to retain regular sleeping patterns to promote well-being and mental health.