Recruitment

Recruitment took place from the November 1st, 2017, until December 12th, 2023. Multiple paths of recruitment were used for the OS. Main sources of recruitment were social media platforms, such as Instagram, Facebook and Twitter/X, websites and online forums, including search-engine-based advertising via Google Ads. Additionally, flyers and posters were printed and distributed to clinical centres, outpatient settings, schools, and universities, with a focus on the surrounding area of the different centres. Further, for the NSSI sample, child and adolescent patients at the participating hospitals and outpatient clinics were directly invited to participate in the study. Registration for the project was centralised via the project website (https://star-projekt.de), where participants found information on the study and on NSSI. Inclusion criteria varied according to the subprojects. Inclusion criteria for HCs were participants age between 15 and 25 years, sufficient German language skills, no lifetime history of NSSI, no current mental disorder according to the DSM-5, and no current psychiatric or psychotherapeutic treatment. For inclusion in the online assessment of STAR ASSESS participants had to be between 15 and 25 years of age, have sufficient German language skills and report history of at least one NSSI incident in the last 12 months. To participate in STAR NEURO or STAR EMA and the accompanying f2f interviews, participants needed to report NSSI on five or more days within the last 12 months (criterion A in the DSM-5). To participate in the fMRI study, participants had to be able to travel to one of two available centres, in which fMRI scanning took place. Exclusion criteria for STAR NEURO and STAR EMA were substance or alcohol dependency of a severity to fulfil substance abuse criteria as defined in the DSM-5 within the last three months, pregnancy, epilepsy, acute suicidality that required immediate inpatient treatment, autism spectrum disorder, acute psychosis, or mental retardation. Specific exclusion criteria within the fMRI study included claustrophobia, metal parts in the body and a known history of brain alterations (e.g., tumour, epilepsy).

Procedures

After registration and written informed consent, psychopathology of the participants with NSSI was assessed online (see details below) at baseline (T0), 4 (T1), 12 (T2), and 18 (T3) months after the initial baseline assessment, to follow the course of NSSI and to assess potential predictors for NSSI (STAR ASSESS (online part)). In addition, participants were asked online whether they resided near one of the study centres, so that they could participate in the face-to-face assessment part of the STAR NEURO and STAR EMA study. If participants of the online assessment were eligible due to their place of living and agreed to participate in the f2f part, eligibility was further assessed via a telephone screening and informed consents were obtained. Within the f2f subsample, a smaller female sample was recruited for an fMRI study. In addition, the f2f subsample was followed up by phone at T3 in addition to the usual T3 online follow-up, in order to gain deeper insights into relevant variables. The HC group participated in STAR ASSESS face-to-face (f2f), STAR NEURO, and STAR EMA. In contrast to the NSSI group, the psychopathology of HCs was only assessed at baseline (T0). For a precise description of the participation process, please see Fig. 2. At T0 in- and exclusion criteria were checked.

Fig. 2

Flowchart of the participation process for the NSSI group for STAR NEURO, STAR EMA (ecological momentary assessments), and STAR ASSESS. Green rectangles: STAR ASSESS, grey rectangles: STAR NEURO and STAR EMA

Ethical aspects

Study procedures for the STAR ASSESS (online part) were first reviewed by the Institutional Review Board (IRB) of the Medical Faculty of Heidelberg (University of Heidelberg), with recruiting centres also receiving approval from their respective IRB (University of Ulm, Medical Faculty of Mannheim, LEK Department of Psychology, University of Landau). Study procedures for the STAR ASSESS (f2f part), STAR NEURO and STAR EMA study were first reviewed by the IRB of the Medical Faculty Mannheim (University of Heidelberg), as the Mannheim centre took the lead for STAR NEURO, with recruiting centres also receiving approval from their respective IRB (University of Ulm, Medical Faculty of Heidelberg, LEK Department of Psychology, University of Landau). Participants with NSSI first provided online consent for the initial screening part, e.g. including questions regarding age and current NSSI, within STAR ASSESS (online part). For the further study procedure, participants and their caregivers provided written informed assent and consent. Healthy controls completed an online screening with information regarding age, lifetime NSSI, and current treatments. Afterwards, they received the participant information, had the telephone screening, and lastly, they and/or their parents provided written informed consent prior to the psychological f2f assessment via telephone. Like the NSSI group, informed consent was obtained for the further study procedure. For participants who completed the entire assessment, a compensation of 135€ was paid. In detail, 45€ were paid for the STAR NEURO procedure, 45€ for the fMRI scan, and 30€ for the STAR EMA participation. Additionally, in STAR EMA, participants were given a bonus of 15€, if they completed a minimum of 80% of the EMA prompts, wore the sensor and provided all cortisol samples (see STAR EMA and NEURO daily measurements). In case of dropouts during the diagnostic assessment, an hourly compensation of 10€/hour was paid.

The following sections present the foci of the separate subprojects.

STAR ASSESS psychological assessment

To investigate various psychological predictors, a multi-method approach was used, including self-report questionnaires, an implicit measure, and clinical interviews. Several self-report questionnaires were used in the online assessment to assess sociodemographic data, psychopathology, NSSI severity, difficulties in emotion regulation, and self-efficacy, etc. Psychopathology in parents or other caregivers was investigated with another online questionnaire. For a detailed overview of the online measures see Table 1. Furthermore, exposure to potentially traumatic events, bullying, contagion effects of NSSI, and media consumption, especially related to NSSI, were assessed.

After the online assessment part, a psychological f2f assessment was conducted with the participants of the STAR EMA and STAR NEURO subsamples at T0. To assess the diagnostic criteria of major mental disorders according to the DSM-5, the Diagnostic Interview for Mental Disorders for adolescents (German: Jugendversion des Diagnostischen Interviews bei Psychischen Störungen, J-DIPS) [35], a structured interview, was used, which was modified for the STAR project. The modifications included the elimination of the section for bipolar disorder, gaming disorder, somatic stress disorders, additions related to NSSI from the Kinder-DIPS, and we abridged questions that were irrelevant for a diagnosis. Additionally, the J-DIPS includes questions to assess the research criteria of suicidal behaviour disorder (SBD) and of nonsuicidal self-injury (NSSI) as proposed in the DSM-5 Section III. The J-DIPS open access version with a detailed description of the adjustments made for the STAR project can be found online: (www.ruhr-uni-bochum.de/klipsychologie/dips-interv/kkjp/download/J-DIPS_OA_Gesamt.pdf). In addition, the Zanarini-Rating Scale for Borderline Personality Disorder (ZAN-BPD), with a modified time frame assessing six months instead of one week [36], the clinical global impression (CGI, severity scale), and the five-minute speech sample (FMSS) [37] to assess expressed emotions, were conducted. For the FMSS, the participants were asked to speak about their feelings and thoughts related to their parents or caregivers. The 18-month follow-up assessment of the STAR EMA & NEURO subsample included the J-DIPS, the ZAN-BPD, and the clinical global impression (CGI, severity, and improvement scale). For all assessments, the interviewers received an intensive standardised training.

Table 1 Online questionnaires and tasks assessed at T0, T1, T2, and T3STAR NEURO laboratory assessmentBlade paradigm, genetic analyses, and analysis of the peripheral stress response systems

First, the investigator took a saliva sample for DNA extraction from the participants. Genetic analysis included SNP-Microarray analysis (Illumina Human GSA + Psych Bead Array v4.0) to calculate polygenic risk scores for ADHD, ASD, depression, anxiety, neuroticism [20], to perform quantitative GWAS integrating brain developmental transcriptome data [51], and to explore artificial intelligence (AI)-driven pathways based molecular burden scores as predictors for NSSI-diagnosis and course as well as biological markers such as cortisol reaction levels [52].

To investigate the effect of NSSI on cortisol levels and electrocardiogram (ECG), participants underwent the blade paradigm [53], which by means of a weighed blade allows the simulation of “cutting pain” without any damage to the skin tissue. ECG was continuously recorded at 1024 Hz with an EcgMove 3 sensor (Movisens GmbH; Karlsruhe, Germany), attached to a chest belt with dry electrodes in order to continuously assess heart rate (HR) and HR-variability (HRV). Salivary cortisol was assessed 7 times every 10–15 min starting 25 min before the blade-paradigm and continuing throughout the experiment by chewing on a cotton swap (Salivette®; Sarstedt, Numbrecht, Germany) for one minute respectively. Samples were frozen at -20 °C until assay. In addition, participants rated the perceived pain intensity on a smartphone using a visual analogue scale. Lastly, the investigator cut a thin strand of hair from the back of the head, as close to the scalp as possible for interindividual cortisol analyses. For the analyses of baseline cortisol levels, only the last three centimetres were analysed. Both saliva and hair cortisol samples were analysed at the Biopsychology Laboratory at the Technical University of Dresden. The entire assessment had a duration of approximately five hours and is visualised in Fig. 3.

Fig. 3

f2f assessment at the centres. FMSS = five-minute speech sample, J-DIPS = German: Jugendversion des Diagnostischen Interviews bei Psychischen Störungen, ZAN-BPD = Zanarini-Rating Scale for Borderline Personality Disorder

STAR NEURO fMRI

Participants at the centres Ulm and Mannheim were asked to participate in a functional magnetic resonance imaging study (fMRI). This sub-study focused on emotion regulation and social exclusion. Investigating the neural correlates of emotion regulation, participants were presented with unpleasant or neutral images of a subset of 80 pictures of the IAPS [54] partly coupled with an unpleasant heat stimulus by means of an fMRI-compatible thermode (Ulm: ATS-Thermode, 30 × 30 mm, TSA-II, Medoc Advanced Medical Systems, Ramat Yishai, Israel; Mannheim: CHEPS-Pathway, 30 × 30 mm, Medoc Advanced Medical Systems, Ramat Yishai, Israel). In a second step, they participated in the Cyberball paradigm to evoke social exclusion [55]. Cyberball is a game with three conditions, where the participant is instructed to either observe or participate in a ballgame. The participation conditions either include or exclude the participant from the game, leading to feelings of social inclusion or rejection. Acquisition of magnetic resonance imaging data was performed on a 3 Tesla MAGNETOM Prisma (Siemens AG, Erlangen, Germany) with a 64-channel head/neck coil. The fMRI scan was concluded with another set of questionnaires regarding social exclusion and rating of the IAPS images. Differences between the scanners were statistically controlled for by the study centres.

STAR EMA and NEURO daily measurements

Participants received a study smartphone, which they carried for seven days from Monday to Sunday while going about their everyday lives. The smartphones were programmed using movisensXS (movisens GmbH, Karlsruhe, Germany) to elicit prompts according to an individualized time-based sampling scheme. Participants chose a wake-up time for each of the seven days of the assessment and specified their timetable to only receive prompts in their free time (e.g., after school hours) during weekdays. Thus, participants were asked to answer one assessment in the morning (i.e., the morning assessment) plus hourly assessments during the predefined assessment interval (i.e., repeated assessment every 60 min +/- 10 min from the individualized starting point through 22:00). At the weekends, participants were prompted from their individualised wake-up time until 22:00. The prompted questionnaires measured momentary mechanisms regarding NSSI behaviour. They included morning assessments regarding sleep quality (4 items, 53) and repeated assessments with 25 items regarding affect (valence and arousal with 2 items each, based on the Multidimensional Mood Questionnaire [57], and the intensity of six specific emotions (e.g., shame, self-contempt and anger, with 1 item each), occurrences of NSSI (i.e., acts and urges, 1 item each), dissociative symptoms (4 items [58]),, interpersonal behaviour (2 items), impulsivity (1 item), stress-reactivity and reward experience (1 item each), and momentary self-esteem (4 items, based on [59]). Answering the repeated prompts usually took participants less than one minute. During the respective week of the EMA assessment, participants were also instructed to wear an ECG belt (see above for details) for 48 h from Thursday evening 8 p.m. to Saturday evening 8 p.m. Further, participants provided 4 daily saliva samples on 3 days to quantify the cortisol awakening response (CAR, 3 samples following awakening) in the morning and the diurnal slope in cortisol secretion (additional sample in the evening). Saliva samples were registered with the study smartphones to enable accurate tracking of sampling (see Fig. 4). On the days before the cortisol assessments, participants received an additional set of questions regarding stress anticipation (4 items [60]), in the evenings. All STAR EMA participants are also part of the STAR NEURO subsample and provided additional data on potential confounding variables of interest concerning biological samples (e.g., hormonal contraceptives, general medication intake and regular intake of medication containing glucocorticoids, physical illness).

Fig. 4

STAR EMA/NEURO assessment. LAB: f2f assessment in the laboratory; EMA (ecological momentary assessments): assessments via smartphone during participants’ daily lives; CAR: Cortisol awakening response, saliva sampling in the morning and evening; ECG: wearing of the ECG belt from Thursday evening until Saturday evening