Table 1.
Main study characteristics
| Study | Participant characteristics | Subtypes | Comorbid conditions | Intervention | Main outcome | Other outcomes | Findings | ||
|---|---|---|---|---|---|---|---|---|---|
| N | Age | Sex | |||||||
| Stadler et al. (2007)*† | 22 | 10.91 (1.77) | M | Not specified | N = 6, CD | ATD/BAL | Reactive aggression (PSAG) | Trait aggression + trait attention (CBCL) | Low Provocation (LP) trials: increased aggression under ATD. High provocation (HP) trials: increased aggression in both ATD and placebo conditions. No relationship with trait attention/aggression |
| Zepf et al. (2008a) | 22 | 10.91 (1.77) | M | 22 combined type | N = 6, CD | ATD/BAL | Behavioural inhibition (Go/No-go task) | Trait aggression (Buss-Perry) | High hostile participants had more inhibition errors under ATD; low hostile participants showed fewer errors under ATD |
| Zepf et al. (2008c) | 22 | 10.91 (1.77) | M | Not specified | N = 6, CD | ATD/BAL | Reaction time (PSAG) | Trait attention + trait aggression + anxiousness/depressiveness (CBCL) | Positive correlation between delta HP and scores on CBCL-PBD scores. High scores had slower reaction time (RT) under ATD; low scores had faster RT under ATD |
| Zepf et al. (2008b) | 22 | 10.91 (1.77) | M | Not specified | N = 6, CD | ATD/BAL | Reactive aggression (PSAG) | Trait aggression (Buss-Perry) + trait impulsivity (IVE) | LP trials: no difference in reactive aggression under ATD. LP trials negatively correlated with trait impulsivity. HP trials: no difference in reactive aggression under ATD |
| Zepf et al. (2009a) | 17 | 11.18 (1.81) | M | Not specified | Not specified | ATD/BAL | Mood (EWL) | Trait impulsivity (IVE) | No effect of ATD on mood ratings nor trait impulsivity |
| Zepf et al. (2009b) | 16 | 11.25 (1.84) | M | Not specified | N = 2, CD | ATD/BAL | Heart rate (HR) (Polar S810) | Trait impulsivity (IVE) | Low impulsive group: lower HR under ATD. High impulsive group: no difference in HR under ATD/placebo |
| Zepf et al. (2010) | 22 | 10.9 (1.8) | M | Not specified | N = 6, CD | ATD/BAL | Attention (test for attentional performance) | – | Lapses of attention were higher in the placebo group compared to ATD 120 min (T1) on. This difference does not hold at T2 (220 min) and T3 (300 min) |
| Zimmermann et al. (2012)*† | 20:20 | 30.25 (9.37)/27.90 (6.01) | M | 13 combined type, 7 inattentive | Not specified | ATD/BAL | Reactive aggression (PSAG) | Trait impulsivity (BIS) | LP trials: lower aggression under ATD in ADHD adults (opposite effect in controls). HP trials: no difference in any of the groups |
| Mette et al. (2013) | 20:20 | 30.25 (9.37)/27.90 (6.01) | M | 13 combined type, 7 inattentive | Not specified | ATD/BAL | Attention (modified CPT) | – | Group x condition: RT improved under ATD for the ADHD group and worsened in the HC group. More omission errors under ATD in both groups |
| Zepf et al. (2013) | 22 | 10.95 (1.17) | M | Not specified | N = 4, CD | ATD/BAL | Verbal declarative memory (AVLT) | – | No effect of ATD on declarative memory |
| Kötting et al. (2013)*† | 20 | 11.80 (1.88) | 10 M:10F | Not specified | Not specified (but CD tolerated) | ATD/BAL | Reactive aggression (PSAG) | – | LP trials: increased aggression under ATD in female participants, no difference in male participants. HP trials: increased aggression under ATD in male participants |
| Grabemann et al. (2013) | 20:20 | 30.25 (9.37)/27.90 (6.01) | M | 13 combined type, 7 inattentive | Not specified | ATD/BAL | Affective prosody (Tubingen Affect Battery) | Decision time (PSAG) + trait impulsivity (IVE) | No sig effect of condition on affective prosody and no group x treatment interaction. Sig interaction between group and correct responses = > the ADHD group had fewer correct responses on the second subtask |
| Von Polier et al. (2014) | 15 | 11.8 (1.9) | 7 M:8F | Not specified | Not specified | ATD/BAL | Hyperactivity (electrodermal activity) | Reactive aggression (PSAG) | No condition x SCR amplitudes nor gender x condition interaction. Change in SCR under ATD neg correlated with baseline aggression |
| Biskup et al. (2016)† | 12:10 | 15.5 (1.7)/16.1 (1.7) | M | Not specified | None | ATD/BAL | Default Mode Network (DMN) connectivity (rs-fMRI) | – | Differential functional connectivity between DMN and premotor cortex, somatosensory cortex under ATD in ADHD |
M, Male, F, Female; CD, Conduct Disorder; ATD, Acute Tryptophan Depletion, BAL, Balanced; PSAG, point-subtraction aggression game, EWL, mood rating scale, ALVT, Auditory Verbal-Learning-Test; CBCL, Child Behaviour Check List, IVE, Eysenck’s Impulsivity Inventory/Impulsiveness and Venturesomeness Questionnaire, BIS, Barratt Impulsiveness Scale; LP, Low provocation, RTD, Rapid tryptophan depletion test; HP, High provocation, PBD, Pediatric bipolar disorder, RT, Reaction Time, HR, Heart rate.
Studies with * were included in the meta-analysis. The four studies bolded and marked with † are the only studies using independent samples.