Annual Research Review: A probe into sensitive periods – how the developmental timing of adverse childhood experiences influences brain structure and function – a systematic review

It is proposed that adverse childhood experiences (ACEs) – potent predictors of mental illness – exert time‐dependent effects on neurodevelopment, reflecting periods of heightened neuroplasticity and developmental sensitivity. We systematically reviewed neuroimaging studies examining the role of timing in the association of ACE exposure with brain structure and function across the lifespan. Across 43 studies spanning childhood to adulthood, findings most consistently implicate earlier onset and longer duration of adversity in alterations to limbic and paralimbic regions, including the hippocampus, amygdala, cerebellum and global brain measures. However, evidence for discrete sensitive periods is mixed and varies by brain system, outcome and analytic approach, with no consistent pattern of sensitive periods emerging across adversity types and functional neuroimaging studies remaining comparatively limited. Progress in the field is further constrained by substantial conceptual and methodological heterogeneity, including inconsistent operationalisation of sensitive periods, reliance on retrospective ACE measures and predominantly cross‐sectional designs. Moving forward, we argue that advancing the field will require reconceptualising sensitive periods as probabilistic, system‐specific and shaped by the nature, timing and chronicity of adversity, rather than as fixed developmental windows. Integrating longitudinal assessment of adversity and neurodevelopment with measures of the neurobiological processes underlying plasticity may help determine whether sensitive periods are better characterised by underlying neuroplasticity than chronological age alone. Improved understanding of these developmental processes may ultimately help inform the timing and targeting of preventive and therapeutic interventions for young people exposed to adversity.