Development
Cognitive Performance in ADHD and Schizophrenia Over 25 Years
Open access · cc by · source: Europe PMC
While individuals with early-onset schizophrenia experience an arrest in cognitive development during early adulthood without further decline, those with ADHD show a delayed maturation that eventually catches up to healthy peers.
Key findings
From baseline to 13 years, the schizophrenia group deteriorated, showing a decrease of −0.053 composite units annually compared to healthy controls, while the ADHD and control groups improved. From 13 to 25 years, however, the schizophrenia group improved significantly faster than controls by 0.03 units per year, showing cognitive stabilization. By the end of the 25-year span, the ADHD group successfully caught up to controls, exhibiting a large improvement effect size of 1.03 compared to the control group improvement effect size of 1.05.
Methodology
Researchers followed cognitive development over 25 years in individuals diagnosed in youth with early-onset schizophrenia, ADHD, or no psychiatric conditions. The study baseline included 19 participants with early-onset schizophrenia, 20 with ADHD, and 30 healthy controls. These groups completed a robust neuropsychological test battery at baseline, a 13-year follow-up, and a final follow-up to analyze changes in a global cognitive composite score.
Limitations
This study cannot establish a direct causal link between the disorders and cognitive changes because it did not control for medication use or fluctuating psychiatric symptoms. The small sample size restricts statistical power and limits how broadly these findings can be applied to all patients. Additionally, the ADHD cohort was entirely male, and there was a significant baseline age difference between the ADHD and control groups. Finally, the use of a broad composite score may hide distinct developmental trajectories in specific cognitive sub-domains.
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