Dissociable neural correlates of tonic and phasic irritability during reward processing in young children.

BACKGROUND: Irritability is a common and impairing feature of childhood psychopathology and is increasingly conceptualized as comprising tonic (persistent irritable mood) and phasic (reactive temper outbursts) components. Although these dimensions show partially distinct behavioral correlates, it remains unknown whether they map onto separable neural mechanisms. This study examined whether tonic and phasic irritability show differential associations with neural activation and connectivity during reward processing in early childhood. Early childhood is a critical period for investigation because impairing irritability can first be reliably identified and tonic and phasic components are already distinguishable. METHODS: Participants were 160 children (mean age = 6.17 years, SD = 0.50; 52.5% female) recruited from the community using an irritability-enriched screening design. Caregiver-reported tonic and phasic irritability were assessed at screening using the Tonic and Phasic Irritability Scale (TAPIS). Children completed a developmentally adapted reward task during functional magnetic resonance imaging (fMRI). Whole-brain activation and generalized psychophysiological interaction connectivity analyses examined interactions among tonic irritability, phasic irritability, and task condition (reward vs. no reward; hit vs. miss), controlling for demographic covariates. RESULTS: Tonic and phasic irritability interacted to predict neural activation and connectivity across frontostriatal and limbic networks during reward anticipation and feedback. Tonic irritability was associated with greater reward-related neural differentiation primarily when phasic irritability was low, whereas this differentiation was attenuated at higher phasic irritability. Independent effects also emerged, with tonic irritability linked to altered ventral striatal connectivity during nonreward and performance failure contexts, and phasic irritability associated with increased amygdala-prefrontal and striatal-cingulate differentiation between reward and nonreward conditions. CONCLUSIONS: Findings provide novel evidence that tonic and phasic irritability correspond to partially dissociable neural processes as early as early childhood. Parsing irritability into chronic versus reactive components may refine neurodevelopmental models and inform more targeted intervention approaches.