Stijn Agus Adrianus Massar
Email Address
mdcsaam@nus.edu.sg
Organizational Units
YONG LOO LIN SCH OF MEDICINE
faculty
DUKE-NUS MEDICAL SCHOOL
faculty
MEDICINE
dept
11 results
Publication Search Results
Now showing 1 - 10 of 11
Publication Evaluating a multi-sensor approach for assessing sleep using wearable and smartphone technology(WILEY, 2020-09-01) Chua, XY; Massar, SAA; Ng, A; Ong, JL; Soon, CS; Chee, NIYN; Chee, MWL; Dr Chun Siong Soon; DEAN'S OFFICE (DUKE-NUS MEDICAL SCHOOL); DUKE-NUS MEDICAL SCHOOLPublication Resting-state EEG theta activity and risk learning: Sensitivity to reward or punishment?(2014-03) Massar, S.A.A.; Kenemans, J.L.; Schutter, D.J.L.G.; DUKE-NUS GRADUATE MEDICAL SCHOOL S'POREIncreased theta (4-7. Hz)-beta (13-30. Hz) power ratio in resting state electroencephalography (EEG) has been associated with risky disadvantageous decision making and with impaired reinforcement learning. However, the specific contributions of theta and beta power in risky decision making remain unclear. The first aim of the present study was to replicate the earlier found relationship and examine the specific contributions of theta and beta power in risky decision making using the Iowa Gambling Task. The second aim of the study was to examine whether the relation were associated with differences in reward or punishment sensitivity. We replicated the earlier found relationship by showing a positive association between theta/beta ratio and risky decision making. This correlation was mainly driven by theta oscillations. Furthermore, theta power correlated with reward motivated learning, but not with punishment learning. The present results replicate and extend earlier findings by providing novel insights into the relation between thetabeta ratios and risky decision making. Specifically, findings show that resting-state theta activity is correlated with reinforcement learning, and that this association may be explained by differences in reward sensitivity. © 2013 Elsevier B.V.Publication Working-from-home persistently influences sleep and physical activity 2 years after the Covid-19 pandemic onset: a longitudinal sleep tracker and electronic diary-based study(Frontiers Media SA, 2023) Massar, Stijn AA; Ong, Ju Lynn; Lau, TeYang; Ng, Ben KL; Chan, Lit Fai; Koek, Daphne; Cheong, Karen; Chee, Michael WL; Dr Stijn Agus Adrianus Massar; MEDICINE; DEAN'S OFFICE (DUKE-NUS MEDICAL SCHOOL)ObjectiveWorking from home (WFH) has become common place since the Covid-19 pandemic. Early studies observed population-level shifts in sleep patterns (later and longer sleep) and physical activity (reduced PA), during home confinement. Other studies found these changes to depend on the proportion of days that individuals WFH (vs. work from office; WFO). Here, we examined the effects of WFH on sleep and activity patterns in the transition to normality during the later stages of the Covid-19 pandemic (Aug 2021–Jan 2022).MethodsTwo-hundred and twenty-five working adults enrolled in a public health study were followed for 22 weeks. Sleep and activity data were collected with a consumer fitness tracker (Fitbit Versa 2). Over three 2-week periods (Phase 1/week 1–2: August 16–29, 2021; Phase 2/week 11–12: October 25–November 7, 2021; Phase 3/week 21–22: January 3–16, 2022), participants provided daily Fitbit sleep and activity records. Additionally, they completed daily phone-based ecological momentary assessment (EMA), providing ratings of sleep quality, wellbeing (mood, stress, motivation), and information on daily work arrangements (WFH, WFO, no work). Work arrangement data were used to examine the effects of WFH vs. WFO on sleep, activity, and wellbeing.ResultsThe proportion of WFH vs. WFO days fluctuated over the three measurement periods, mirroring evolving Covid restrictions. Across all three measurement periods WFH days were robustly associated with later bedtimes (+14.7 min), later wake times (+42.3 min), and longer Total Sleep Time (+20.2 min), compared to WFO days. Sleep efficiency was not affected. WFH was further associated with lower daily step count than WFO (−2,471 steps/day). WFH was associated with higher wellbeing ratings compared to WFO for those participants who had no children. However, for participants with children, these differences were not present.ConclusionPandemic-initiated changes in sleep and physical activity were sustained during the later stage of the pandemic. These changes could have longer term effects, and conscious effort is encouraged to harness the benefits (i.e., longer sleep), and mitigate the pitfalls (i.e., less physical activity). These findings are relevant for public health as hybrid WHF is likely to persist in a post-pandemic world.Publication Genetic polymorphisms of the dopamine and serotonin systems modulate the neurophysiological response to feedback and risk taking in healthy humans(2012-12) Heitland, I.; Oosting, R.S.; Baas, J.M.P.; Massar, S.A.A.; Kenemans, J.L.; Böcker, K.B.E.; DUKE-NUS GRADUATE MEDICAL SCHOOL S'POREGenetic differences in the dopamine and serotonin systems have been suggested as potential factors underlying interindividual variability in risk taking and in brain activation during the processing of feedback. Here, we studied the effects of dopaminergic (dopamine transporter [DAT1], catecholamine-O-methyltransferase val158met [COMT]) and serotonergic (serotonin transporter [5HTTLPR]) polymorphisms on risk taking and brain responses following feedback in 60 healthy female subjects. The subjects completed a well-established experimental gambling paradigm while an electroencephalogram was recorded. During the task, risk-taking behavior and prefrontal brain responses (feedback-related negativity [FRN]) following monetary gains and losses were assessed. FRN amplitudes were enhanced for nine-repeat-allele carriers of the DAT1 and short-allele carriers of 5HTTLPR, which are both presumably linked to less transporter activity and higher neurotransmitter levels. Moreover, nine-repeat DAT1 carriers displayed a trend toward increased risk taking in general, whereas 5HTTLPR short-allele carriers showed decreased risk taking following gains. COMT val158met genotype was unrelated to FRN amplitude and average risk taking. However, COMT met/met carriers showed a pronounced feedback P3 amplitude independent of valence, and a gradual increase in risk taking during the gambling task. In sum, the present findings underline the importance of genetic variability in the dopamine and serotonin systems regarding the neurophysiology of feedback processing. © The Author(s) 2012.Publication Reopening after lockdown: the influence of working-from-home and digital device use on sleep, physical activity, and wellbeing following COVID-19 lockdown and reopening(OXFORD UNIV PRESS INC, 2022-01-11) Massar, Stijn AA; Ng, Alyssa SC; Soon, Chun Siong; Ong, Ju Lynn; Chua, Xin Yu; Chee, Nicholas IYN; Lee, Tih Shih; Chee, Michael WL; Dr Chun Siong Soon; MEDICINE; DUKE-NUS MEDICAL SCHOOLStudy Objectives: COVID-19 lockdowns drastically affected sleep, physical activity, and wellbeing. We studied how these behaviors evolved during reopening the possible contributions of continued working from home and smartphone usage. Methods: Participants (N = 198) were studied through the lockdown and subsequent reopening period, using a wearable sleep/activity tracker, smartphone-delivered ecological momentary assessment (EMA), and passive smartphone usage tracking. Work/study location was obtained through daily EMA ascertainment. Results: Upon reopening, earlier, shorter sleep and increased physical activity were observed, alongside increased self-rated stress and poorer evening mood ratings. These reopening changes were affected by post-lockdown work arrangements and patterns of smartphone usage. Individuals who returned to work or school in-person tended toward larger shifts to earlier sleep and wake timings. Returning to in-person work/school also correlated with more physical activity. Contrary to expectation, there was no decrease in objectively measured smartphone usage after reopening. A cluster analysis showed that persons with relatively heavier smartphone use prior to bedtime had later sleep timings and lower physical activity. Conclusions: These observations indicate that the reopening after lockdown was accompanied by earlier sleep timing, increased physical activity, and altered mental wellbeing. Moreover, these changes were affected by work/study arrangements and smartphone usage patterns.Publication Trait-like nocturnal sleep behavior identified by combining wearable, phone-use, and self-report data(NATURE PORTFOLIO, 2021-06-02) Massar, Stijn AA; Chua, Xin Yu; Ng, Alyssa SC; Ong, Ju Lynn; Chee, Nicholas IYN; Lee, Tih Shih; Ghosh, Arko; Chee, Michael WL; Dr Chun Siong Soon; MEDICINE; DUKE-NUS MEDICAL SCHOOLUsing polysomnography over multiple weeks to characterize an individual’s habitual sleep behavior while accurate, is difficult to upscale. As an alternative, we integrated sleep measurements from a consumer sleep-tracker, smartphone-based ecological momentary assessment, and user-phone interactions in 198 participants for 2 months. User retention averaged >80% for all three modalities. Agreement in bed and wake time estimates across modalities was high (rho = 0.81–0.92) and were adrift of one another for an average of 4 min, providing redundant sleep measurement. On the ~23% of nights where discrepancies between modalities exceeded 1 h, k-means clustering revealed three patterns, each consistently expressed within a given individual. The three corresponding groups that emerged differed systematically in age, sleep timing, time in bed, and peri-sleep phone usage. Hence, contrary to being problematic, discrepant data across measurement modalities facilitated the identification of stable interindividual differences in sleep behavior, underscoring its utility to characterizing population sleep and peri-sleep behavior.Publication Quantifying the Motivational Effects of Cognitive Fatigue Through Effort-Based Decision Making(FRONTIERS MEDIA SA, 2018-05-30) Massar, Stijn AA; Csatho, Arpad; Van der Linden, Dimitri; Dr Stijn Agus Adrianus Massar; DEAN'S OFFICE (DUKE-NUS MEDICAL SCHOOL)Publication Inter-relationships between changes in stress, mindfulness, and dynamic functional connectivity in response to a social stressor(Springer Science and Business Media LLC, 2022-12-01) Teng, J; Massar, SAA; Lim, J; Dr Stijn Agus Adrianus Massar; MEDICINE; DUKE-NUS MEDICAL SCHOOLWe conducted a study to understand how dynamic functional brain connectivity contributes to the moderating effect of trait mindfulness on the stress response. 40 male participants provided subjective reports of stress, cortisol assays, and functional MRI before and after undergoing a social stressor. Self-reported trait mindfulness was also collected. Experiencing stress led to significant decreases in the prevalence of a connectivity state previously associated with mindfulness, but no changes in two connectivity states with prior links to arousal. Connectivity did not return to baseline 30 min after stress. Higher trait mindfulness was associated with attenuated affective and neuroendocrine stress response, and smaller decreases in the mindfulness-related connectivity state. In contrast, we found no association between affective response and functional connectivity. Taken together, these data allow us to construct a preliminary brain-behaviour model of how mindfulness dampens stress reactivity and demonstrate the utility of time-varying functional connectivity in understanding psychological state changes.Publication Sleep deprived and sweating it out: The effects of total sleep deprivation on skin conductance reactivity to psychosocial stress(Associated Professional Sleep Societies,LLC, 2015) Liu, J.C.J; Verhulst, S; Massar, S.A.A; Chee, M.W.L; YALE-NUS COLLEGE; DUKE-NUS MEDICAL SCHOOLStudy Objectives: We examined how sleep deprivation alters physiological responses to psychosocial stress by evaluating changes in skin conductance.Design: Between-subjects design with one group allocated to 24 h of total sleep deprivation and the other to rested wakefulness.Setting: The study took place in a research laboratory.Participants: Participants were 40 healthy young adults recruited from a university.Interventions: Sleep deprivation and feedback.Measurements and Results: Electrodermal activity was monitored while participants completed a difficult perceptual task with false feedback. All participants showed increased skin conductance levels following stress. However, compared to well-rested participants, sleep deprived participants showed higher skin conductance reactivity with increasing stress levels.Conclusions: Our results suggest that sleep deprivation augments allostatic responses to increasing psychosocial stress. Consequentially, we propose sleep loss as a risk factor that can influence the pathogenic effects of stress.Publication Towards an Objective Measure of Mindfulness: Replicating and Extending the Features of the Breath-Counting Task(Springer, 2018) F. Wong, K.; A. A. Massar, S.; Chee, M.W.L.; Lim, J.; DUKE-NUS MEDICAL SCHOOLDespite calls for objective measures of mindfulness to be adopted in the field, such practices have not yet become established. Recently, a breath-counting task (BCT) was proposed as a reliable and valid candidate for such an instrument. In this study, we show that the psychometric properties of the BCT are reproducible in a sample of 127 Asian undergraduates. Specifically, accuracy on the BCT was associated with everyday lapses and sustained attention, and weakly associated with subjectively measured mindfulness. BCT metrics also showed good test-retest reliability. Extending the use of the paradigm, we further found that two different types of task errors—miscounts and resets—were correlated with different aspects of cognition. Miscounts, or errors made without awareness, were associated with attentional lapses, whereas resets, or self-caught errors, were associated with mind-wandering. The BCT may be a suitable candidate for the standardized measurement of mindfulness that could be used in addition to mindfulness questionnaires. © 2018, The Author(s).