Inhibition moderates the effect of attentional bias modification for reducing residual depressive symptoms: A randomized sham-controlled clinical trial

Objectives

Residual symptoms represent risk factor for relapse. Attention bias modification (ABM) may reduce clinical and sub-clinical depressive symptoms, indicating that is may be of relevance when preventing relapse. Current evidence suggests that executive functions may moderate the outcome of interventions targeting depressive symptoms.

Methods

We assessed inhibition and shifting as indicators of executive functioning by means of the Color-Word Interference Test (i.e., “Stroop task”). These baseline characteristics were investigated as moderator of the effect of ABM on depression symptoms in a double-blinded randomized sham-controlled trial of ABM including patients with a history of recurrent depression (N = 301). Inclusion and follow-ups took place from January 2015 to October 2016. The trial was retrospectively registered #NCT02658682 January 2016.

Results

The moderation analysis was based on the interaction term ABM x Stroop. Scaled inhibition scores ≤10.8, but not shifting ability, moderated the effect of ABM compared to sham on clinician-rated depression (HDRS). The difference from the 15th to the 85th percentile of the inhibition score was about 1 HDRS-point, indicating a small effect size. No moderation was found when self-reported depression and AB were the outcome. Post-hoc power calculation indicates risk of Type-II error.

Conclusion

When targeting depressive symptoms, ABM seems to be somewhat more effective in patients with weak inhibitory control. This suggests that evaluating the level of inhibition in individual patients could provide some information when making decisions about prescribing ABM to reduce residual symptoms, but the clinical implications of this is uncertain due to an overall small effect size attributable to ABM. Future studies should examine whether inhibitory control still is a relevant moderator when comparing ABM to treatment options other than the sham control condition.