Cognitive Performance in ADHD and Schizophrenia Over 25 Years
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.
Source
Cognitive Performance in Early-Onset Schizophrenia and Attention-Deficit/Hyperactivity Disorder: A 25-Year Follow-Up Study
What they did
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.
What they found
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.
The limits
What it doesn't show
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.
Key terms
- Early-Onset Schizophrenia (EOS)
- A severe neurodevelopmental disorder characterized by psychosis and cognitive deficits, diagnosed before the age of 18.
- Attention-Deficit/Hyperactivity Disorder (ADHD)
- A neurodevelopmental disorder marked by persistent patterns of inattention, hyperactivity, and impulsivity.
- Maturational Lag Hypothesis
- The theory that cognitive deficits in certain developmental disorders result from a delay in brain maturation that eventually catches up to normal levels.
- Neurodegenerative Model
- A framework proposing that a clinical condition leads to progressive, ongoing deterioration of brain structures and cognitive functions over time.
- Cognitive Composite Score
- An aggregated value calculated by averaging scores across multiple individual cognitive tests to estimate overall intellectual functioning.
- Linear Mixed Models
- A statistical technique used to analyze longitudinal data by accounting for both group-level trends and individual variations over time.
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Quiz yourself
What was the main aim of this 25-year longitudinal follow-up study?
Common questions
Did the cognitive abilities of individuals with schizophrenia continuously decline over time?
No. While they experienced a cognitive decline or stagnation from adolescence into their twenties, their cognitive scores stabilized and even improved during their thirties and forties, which argues against a neurodegenerative progress.
How did the ADHD group fare over the 25-year period?
The ADHD group showed continuous cognitive maturation well into their thirties, supporting the theory of a developmental delay that eventually resolves or catches up to healthy peers.
Were the effects of psychiatric medications controlled for in this research?
No, the study did not control for the potential confounding effects of antipsychotics or stimulants on long-term cognitive trajectories, which is a key limitation.
Why was the inclusion of a healthy control group necessary?
The healthy control group allowed researchers to compare the cognitive trajectories of the clinical groups against normal, age-associated changes in brain maturation.
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