Serotonin (5-HT) critically regulates cognitive and emotional functions, and both stable and transient variations in 5-HT signaling have been associated with emotional dysregulations. However, findings regarding the neurofunctional effects of transient 5-HT variations have been highly inconsistent. Therefore, we examined whether individual variations in a central 5-HT-regulating genetic polymorphism (tryptophan hydroxylase 2, TPH2) represent a vulnerability or resilience factor for the effects of acute tryptophan depletion (ATD) on functional brain architecture. The current study utilized a pharmacogenetic within-subject randomized placebo-controlled resting-state fMRI design with N = 53 healthy male participants in combination with spontaneous intrinsic neural activity, functional connectivity, and connectome gradient analyses to compare the neurofunctional effects of ATD-induced transient reduction in central 5-HT signaling between TPH2 genotypes (a priori genotyping for rs4570625, GG n = 25 vs. TT n = 23). ATD induced significant increases in spontaneous neural activity in hippocampal CA1 irrespective of genotype and enhanced communication of this region with the bilateral amygdala and the vmPFC specifically in GG carriers. ATD sharpened the intrinsic connectome gradient architecture in several large-scale networks, including the salience, frontoparietal, and default mode network. Our results identify a potential genetic marker for an increased vulnerability to the neural effects of transient variations in 5-HT signaling on the functional architecture of an anxiety- and stress-related brain circuit in men. Gradient architecture results underscore the regulatory role of 5-HT on the intricate organization of large-scale networks involved in emotional reactivity and regulation.

This work presents a policy analysis regarding Problematic Usage of the Internet (PUI) across seven countries (Netherlands, Spain, Hungary, Lithuania, Portugal, Estonia, and Switzerland) belonging to or associated with the European Union (EU). I It examines legislative instruments addressing PUI and its multifaceted impacts on society, including social, economic, and political dimensions. Despite the growing prevalence of PUI, particularly among adolescents, and its association with various mental health concerns, the study reveals a notable gap in direct policy interventions targeting PUI within these countries. Existing regulations largely focus on broader digital governance issues like data protection, cybersecurity, and market regulation, offering only indirect approaches to mitigating PUI's adverse effects. Our findings highlight a pressing need for innovative policy frameworks that incorporate mental health considerations into digital governance, promoting a balanced approach that fosters market innovation while ensuring robust public health protections. Building on the policy discourse examined in this study, future research should focus on developing targeted, multidimensional strategies to mitigate the risks associated with problematic internet use (PUI), with particular emphasis on safeguarding the well-being of vulnerable populations.

We evaluate the contemporary societal belief that social media use causes mental health problems among adolescents, such as depressive and eating disorders, and suicide. We alternatively raise the more likely scenario that poor mental health is what can drive social media use/overuse. We summarize empirical evidence from longitudinal studies on relations between social media use/overuse and mental health among adolescents, demonstrating mixed findings and important methodological limitations that preclude our ability to state that social media use is a major cause of mental disorder. Nonetheless, we discuss the need for government regulation of social media companies, given that these companies have purposefully promoted excessive social media use in adolescents, and have inadequately protected against violent content and misinformation on their platforms. Social media use/overuse is not likely a major cause of mental disorder, but can nonetheless result in other harms.

ABSTRACT Importance Problematic use of the internet (PUI) behaviors, including problematic gaming, social media use, smartphone use, and general internet use, have been increasingly studied worldwide. So far it is unclear what the global prevalence of PUI is. Objective To critically appraise existing systematic reviews and meta-analyses on the prevalence of PUI behaviors and generate aggregated global prevalence estimates across different manifestations and definitions. Data Sources MEDLINE (Ovid), Embase (Ovid), Scopus, Web of Science, CINAHL, and the Cochrane Review Library were searched for relevant articles from database inception to the most recent available search prior to manuscript preparation. Searches targeted systematic reviews and meta-analyses reporting prevalence for PUI-related behaviors. Study Selection Systematic reviews and meta-analyses of observational studies reporting prevalence estimates for problematic gaming, problematic internet use, problematic smartphone use, problematic social media use, or sexting were included. Scoping reviews were retained for descriptive synthesis only. Data Extraction and Synthesis An umbrella review methodology was used. Data extraction and methodological appraisal were conducted using AMSTAR-2 to assess the quality of included systematic reviews up to February 2026. Primary studies included in each review were extracted and pooled using random-effects meta-analysis. Analyses were conducted to estimate pooled prevalence with 95% confidence intervals (CIs) and heterogeneity across non-overlapping primary studies. Small-study effects were examined. Main Outcomes and Measures Global pooled prevalence estimates for PUI behaviors, including problematic gaming, problematic internet use, problematic smartphone use, problematic social media use, and sexting. Results Eleven reviews (10 systematic reviews and 1 scoping review) met inclusion criteria, representing data from 3 145 428 individuals, of whom 3 030 023 were included in pooled prevalence analyses. Across regions, pooled prevalence estimates were 6% (95% CI, 5%–7%) for problematic gaming, 16% (95% CI, 15%–17%) for problematic internet use, 32% (95% CI, 28%–35%) for problematic smartphone use, and 23% (95% CI, 19%–28%) for problematic social media use. Substantial heterogeneity (I 2 > 99%) was observed across primary studies, reflecting variation in study methodologies, sampled populations, and definitions of PUI behaviors. Conclusions and Relevance PUI behaviors appear to affect a substantial proportion of the global population. However, methodological concerns were common, with 9 of 10 systematic reviews rated as having low or critically low confidence according to AMSTAR-2. Evidence remains concentrated in East Asia and Europe, and many reviews combine heterogeneous populations and sampling strategies. Additional high-quality epidemiological research, including underrepresented regions is needed to refine prevalence estimates, clarify risk factors, and support the development of standardized criteria for PUI behaviors. Key Points Question What is the global prevalence of problematic use of the internet (PUI) behaviors across major subtypes, based on an umbrella review of existing reviews and a meta-analysis of nonoverlapping primary studies? Findings In this umbrella review of 11 reviews and random-effects meta-analysis of 753 nonoverlapping primary studies including 3 030 023 individuals, pooled prevalence estimates were 6% for problematic gaming, 16% for problematic internet use, 32% for problematic smartphone use, and 23% for problematic social media use. Findings indicated substantial between-study heterogeneity, and most included systematic reviews were rated low or critically low in methodological quality. Meaning These findings suggest that PUI behaviors affect a substantial proportion of the global population, but more methodologically rigorous and geographically representative epidemiological research is needed to generate more precise and comparable prevalence estimates across clinical and population samples.

In digital text communication, real facial emotion expressions are lacking, with emojis serving as substitutes to nonverbally communicate emotions. However, it is widely unknown if emotion expressions in emojis and faces are perceived equivalently. Therefore, two studies were conducted, Study 1 with a German (N = 811) and Study 2 with a UK sample (N = 910), investigating emotion-general (Study 1, 2) and emotion-specific (Study 2) differences between as well as age and gender differences in emotion perception in emojis and faces. The emotion-general emotion perception was higher for emojis than faces in the German sample (Study 1), whereas in the UK sample it was reversed; mainly driven by the emotions disgust, fear and surprise (Study 2). Emotion-general age and gender effects differed across face and emoji stimuli (Study 1, 2). Women performed better than men at perceiving emotions in faces, with a skewed reversed U-shaped pattern across the adult lifespan for both genders (Study 1, 2). Similar findings applied to the emotion-general emotion perception in emojis in the UK sample (Study 2). In the German sample, the emotion perception performance for emojis followed a skewed reversed U-curve across the adult lifespan, with a steeper decline in women than men; thus, women were initially better and then worse than men at perceiving emotions in emojis (Study 1). Emotion-specific gender and age effects were found for emojis and faces (Study 2). This suggests that emotion expressions in emojis and faces are not perceived equivalently, providing new insights for improving online communication.

This study examines the association between the use of so-called "timekeepers", such as traditional wristwatches or classic alarm clocks, or digital "timekeepers" as smartphones or smartwatches, and Internet use disorder. Based on theoretical models it was examined whether certain everyday habits are related to the extent of problematic online behavior. In a cross-sectional online survey (N = 6,615), participants answered the Compulsive Internet Use Scale (CIUS) and questions about their usage behavior in the context of smartphones, wrist watches, and alarm clocks. Participants who stated that their Internet use was excessive or that they stayed online longer than planned after looking at the clock function on their smartphone had significantly higher CIUS scores. The same was true for people who did not wear a watch, used their smartphone as an alarm clock, took it into the bedroom, or went online immediately after waking up. The time of first smartphone use in the morning proved to be a significant predictor of problematic use, whereas the last time using the smartphone before going to bed was not. The findings replicate and extend previous studies and suggest that non-Internet-connected timekeepers are associated with less dysfunctional Internet and smartphone usage patterns. The use of the smartphone as a multifunctional device could be suggested as a potential trigger for unwanted media use. However, targeted everyday modifications - such as the use of classic watches - might contribute to the prevention of Internet use disorder which needs to be tested in future studies.

This work analyses policies related to the Problematic Usage of the Internet (PUI) and its relationships to adolescent mental health across the United Kingdom, France, Germany, Italy, Australia, Canada, the United States, and New Zealand. Using a policy path dependency framework, national legislation was examined to assess relationships with PUI. The study maps policy by reviewing governmental legislation and databases, analysing them on macro (societal), meso (market/intermediary organisations), and micro (citizen rights, duties, and protection) levels. It explores legal instruments related to PUI, including data protection, cybersecurity, content regulation, and harassment, offering both historical and comparative analyses across the eight countries. Findings indicate that while several countries have policies indirectly regulating PUI, significant legislative gaps persist relating to adolescent mental health. Most policies address broader internet concerns without specifically targeting PUI or its effects on mental health. Overall, the analysis highlights the need for more targeted public health policies to address the root causes of PUI, advocating for tailored interventions focused on adolescent well-being.

This work analyses policies related to the Problematic Usage of the Internet (PUI) and its relationships to adolescent mental health across the United Kingdom, France, Germany, Italy, Australia, Canada, the United States, and New Zealand. Using a policy path dependency framework, national legislation was examined to assess relationships with PUI. The study maps policy by reviewing governmental legislation and databases, analysing them on macro (societal), meso (market/intermediary organisations), and micro (citizen rights, duties, and protection) levels. It explores legal instruments related to PUI, including data protection, cybersecurity, content regulation, and harassment, offering both historical and comparative analyses across the eight countries. Findings indicate that while several countries have policies indirectly regulating PUI, significant legislative gaps persist relating to adolescent mental health. Most policies address broader internet concerns without specifically targeting PUI or its effects on mental health. Overall, the analysis highlights the need for more targeted public health policies to address the root causes of PUI, advocating for tailored interventions focused on adolescent well-being.

The present work examines associations between TikTok Use Disorder (TTUD) tendencies, fear of missing out (FoMO) and everyday cognitive failure. In line with prior studies on problematic social media use, we observed in N = 720 TikTok users (249 males, 471 females; mean age = 37.78 years) - who completed the TikTok Use Disorder Questionnaire (TTUD-Q), the FoMO Scale, and the Cognitive Failure Questionnaire (CFQ) - that both higher trait and state FoMO went along with more self-reported cognitive failure in everyday life. This association was mediated by TTUD tendencies, albeit to different degrees. The distinction between general FoMO tendencies and situational, online-related state FoMO appears to be important for understanding putative mechanisms behind the here presented associations and is discussed further. Overall, the findings suggest that higher disordered use tendencies of TikTok may be linked to more cognitive failure, potentially due to frequent app-related interruptions of everyday activities. However, these conclusions are limited by the self-report nature of data and the cross-sectional design which precludes causal inference.

Problematic online behaviors often span multiple digital platforms, yet previous research has focused on single forms of problematic use. It remains unclear whether distinct cross-platform behavioral profiles are associated with differential reward and punishment sensitivity and alterations in brain network topology. This study combined latent profile analysis with resting-state functional magnetic resonance imaging to identify latent risk profiles of cross-platform problematic online behaviors among Chinese university students and examine their motivational and neural correlates. In Study 1, 947 students completed measures of problematic usage of smartphones, video gaming, and social networking, and reward/punishment sensitivity. Latent profile analysis identified three graded profiles: Low-Risk, Medium-Risk, and High-Risk. In Study 2, a stratified subsample of 150 participants underwent resting-state functional magnetic resonance imaging; whole-brain eigenvector centrality (EC) indexed hub-like network properties. The Medium-Risk and High-Risk groups showed higher reward sensitivity than the Low-Risk group, with no difference between at-risk groups. Punishment sensitivity increased stepwise across profiles. Neuroimaging analyses revealed reduced EC in the left superior frontal gyrus and left precuneus in both at-risk groups relative to the Low-Risk group. Lower EC in these regions was associated with greater punishment sensitivity, whereas reward sensitivity showed no significant association with EC. These findings suggest that punishment sensitivity is not only a psychological marker of POB severity but is also associated with reduced hub centrality in the left superior frontal gyrus and left precuneus, indicating a potential neural correlate of heightened sensitivity to negative outcomes.

Background and aims:Literature suggests that individual differences in tendencies toward gaming disorder (GD) may be associated with characteristics of the video games people prefer. We examined how game genre, multiplayer capability, and platform relate to GD tendencies assessed using both APA (DSM-5) and WHO (ICD-11) frameworks in a large international sample of gamers. Methods:We analyzed cross-sectional online data from 116,047 gamers. Participants completed validated measures of GD symptoms aligned with DSM-5 and ICD-11 and reported the genre, multiplayer capability, and platform of their currently preferred game. Associations were examined using bivariate and multivariate analyses. We additionally applied a Random Forest model to evaluate the predictive contribution of game-related variables to GD scores. Results:GD levels were highest among participants preferring games with multiplayer capabilities, while positive associations with shooter and casual games were particularly evident among console users. In contrast, puzzle, platformer, and board games showed negative associations with GD scores. Players preferring desktop or laptop computers reported higher GD scores than those favoring consoles or small devices. In Random Forest models, game genre and multiplayer capability were modestly predictive of GD scores (R ≈ .08-.15) with predictive accuracy being higher for participants who used console and desktop computers and lowest among small-device users. Conclusions:Multiplayer capability and preferred genre were consistently related to GD tendencies across DSM-5 and ICD-11 measures. However, these variables alone offered limited predictive power, indicating that GD risk is only partly explained by game characteristics and likely depends on broader individual and contextual factors.

The prefrontal cortex (PFC) plays a critical role in reward and loss processing, and disruptions in PFC function have been implicated in internet gaming disorder (IGD). However, little is known about how PFC networks coordinate during real-time gaming. A total of 27 individuals meeting criteria for IGD and 28 regular game users (RGU) completed both single-competitive and cooperative-competitive gaming tasks while undergoing functional near-infrared spectroscopy monitoring. The results showed that in the single-competitive mode, during both positive and negative game events, individuals with IGD exhibited lower clustering coefficients, shorter characteristic path length, and higher global efficiency. However, no group differences were observed during cooperative-competitive gameplay. Network-based statistic revealed enhanced functional connectivity between the dorsolateral prefrontal cortex and frontopolar area in the IGD group during negative events in the singlecompetitive mode, and the strength of this connectivity was positively correlated with symptom severity. These findings suggest context-dependent alterations in PFC network topology and connectivity in individuals with IGD, highlighting the importance of examining network-level neural mechanisms underlying reward and loss processing during naturalistic gameplay.

Background and Aims An increasing body of research has demonstrated significant relations between social anxiety and problematic smartphone use (PSU). While some cognitive and affective mechanisms, such as poor emotion regulation, have been explored as mediating variables explaining these relations, there is less known about the role of distress intolerance. Our study explored the mediating role of emotion regulation strategies (expressive suppression and cognitive appraisal) and distress intolerance between social anxiety and PSU severity using structural equation modeling (SEM). We built our research model based upon the framework of the Person-Affect-Cognition-Execution (I-PACE) theoretical model of Internet use disorders.Methods Our sample included 308 undergraduate students aged 18-25 who completed a series of self-report measures.Results SEM results revealed that only expressive suppression significantly mediated the relationship between social anxiety and PSU severity.Conclusion Results support prior research that poor emotion regulation skills serve as an underlying mechanism between psychopathology and PSU. Individuals with social anxiety are more likely to engage in expressive suppression, and therefore PSU. Clinical implications include the need to explore the emotional regulation mechanism underlying the relationship between social anxiety and vulnerability to engage in maladaptive behaviors such as PSU.

The fear of missing out (FOMO) involves two features: apprehension of missing out on rewarding experiences and a desire to stay constantly connected with one’s social network. FOMO is robustly related to problematic Internet use and negative affectivity. However, little research has examined whether these two FOMO dimensions show differential associations with problematic Internet use and negative affectivity. We recruited 388 university students (mean age = 20.06 years, SD = 4.18) at a Midwestern US university for a cross-sectional web survey. We administered self-report measures assessing FOMO, problematic smartphone use (PSU), problematic social media use (PSMU), and several negative affectivity measures. Using confirmatory factor analyses and correlational analyses, we found that in contrast to FOMO’s apprehension dimension, constant connection desire was significantly more highly associated with PSU severity. However, FOMO’s two factors were not differentially associated with PSMU or negative affectivity measures. Results support emerging findings demonstrating that FOMO’s two dimensions are equally related to depression and anxiety, extending this work to other types of negative affectivity (i.e., rumination and distress tolerance). We discuss how negative affectivity is an important aspect of FOMO, and we place our findings within the context of theory.

A substantial proportion of everyday communication in close, interpersonal relationships happens through mobile instant messaging (MIM) services such as WhatsApp. So far, only few studies have focused on relationship-level differences with respect to chatting behavior. Our study seeks to address this gap by combining survey data (N = 357) with donated dyadic WhatsApp chat logs (N = 142) to investigate differences in chatting behavior across different relationship constellations defined by gender combinations, relationship types, and levels of interpersonal closeness. Results show that behavioral metrics representing messaging frequency, expressiveness, reciprocity, and timing substantially vary for different relationship constellations. Using Elastic Net and Random Forest models, the gender combination of chatters and relationship type, but not interpersonal closeness, could be predicted from chatting behavior with significantly better performance than a na & iuml;ve baseline model. We contextualize our findings regarding the literature on interpersonal relationship and communication research, discuss limitations of this study, and provide recommendations for future work.

The present study tested the properties of a cognitive psychometric model for the joint analysis of responses and response times in binding-type working memory capacity (WMC) tasks. These models aim to decompose the task solving process into a set of informative process parameters and to dissociate person and item effects at the same time. Specifically, we fit an IRT-race model with two accumulators to data from three binding-type WMC tests (letter-colour: N = 2,385, word-number: N = 3,898, letter-position: N = 2,272). The accumulator for correct responses (knowledge accumulator) was interpreted as the efficiency of binding processes, the accumulator for incorrect responses (discontinuation accumulator) as a tendency to discontinue the task at hand. The fitted models displayed decent fit to the data. Reliability of the trait estimates across the three tests was satisfactory (omega = 0.86 and omega = 0.76 for the two accumulators). Validity of the trait estimates was investigated through correlations with performance in different working memory updating tests, a test of crystallized intelligence, and with the Big Five personality traits. Notably, the trait estimate for the knowledge accumulator was correlated more strongly with updating performance (r = 0.62) as compared to standard accuracy scores (r = 0.52). Furthermore, there was a moderate negative correlation of the trait estimate for the discontinuation accumulator with Openness (r = -0.26) and with crystallized intelligence (r = -0.26). This study demonstrates that individual differences in process parameters can be incrementally predictive when modelled reliably.

While digital phenotyping has shown potential in linking smartphone use to mental health, there is no evidence on how specific smartphone behaviors are associated with symptom dynamics in borderline personality disorder (BPD) in real time. This study examines how communication versus entertainment app use relates to inner tension and state dissociation, both in terms of momentary associations within individuals and in terms of average associations across individuals. We tracked smartphone use in 49 individuals with BPD during an 8-week inpatient Dialectical Behavior Therapy and concurrently assessed inner tension and state dissociation every two hours. For up to 56 treatment days, we recorded hourly app session usage duration and frequency for communication (e.g., WhatsApp) and entertainment (e.g., Netflix), along with phone calls. Between-person associations based on mean scores for inner tension, state dissociation, and smartphone usage were examined with Spearman correlations. We investigated within-person momentary associations per hour with linear mixed models applied to the first 21 treatment days with sufficient data. Higher mean inner tension levels were linked to longer daily use of communication apps. We found an association between a greater average number of incoming, but not outgoing, phone calls and higher mean levels of inner tension and state dissociation. Within-person analyses related a longer use of entertainment applications to reduced inner tension, but not dissociation, both at the category and at the app level (Netflix and YouTube). In contrast, more frequent communication app uses increased state inner tension and dissociation, which was mirrored in app-level analyses with WhatsApp. Our findings are consistent with a dialectical perspective of smartphone use in BPD: While passive entertainment may represent an adaptive short-term self-regulation strategy, smartphone communication may trigger BPD-related emotional or dissociative responses. Trial registration: https://osf.io/dfq9y/?view_only=4c19b891bb6448009b22f60b2552bd73.