An Investigation of Inhibitory Control as a Mechanism Differentiating Tonic and Phasic Irritability

Phasic and tonic irritability are highly correlated clinical constructs yet differentially associated with developmental trajectories and treatment response. However, limited research has identified their shared and unique underlying behavioral mechanisms. In a sample of youths enriched for irritability (N = 141, age range 7-18, age M[SD] = 12.60[2.54], 48.23% female), we investigated whether inhibitory control is differentially associated with phasic versus tonic irritability. Replicating prior work, tonic and phasic irritability were estimated via independent confirmatory factor analyses (CFAs) using items and/or subscales from multi-informant questionnaires. A latent factor of inhibitory control was extracted from four behavioral tasks. Initial multiple linear regression analysis found that phasic, not tonic, irritability was significantly associated with impaired inhibitory control. However, results were no longer significant after accounting for shared associations with age. In addition, when adding commonly co-occurring symptoms such as attention-deficit/hyperactivity disorder (ADHD) symptoms and oppositionality, age and ADHD were significant predictors of inhibitory control, but phasic irritability was not. Results suggest that inhibitory control alone may not be a salient mechanism for disambiguating phasic and tonic irritability. Future work leveraging longitudinal methods and consideration of other potential contextual factors is needed.