Brain lateralization and self-reported symptoms of ADHD in non-clinical adults: A dimensional approach

Many clinical studies reported a compromised Brain Lateralization (BL) in patients with Attention-Deficit/Hyperactivity Disorder (ADHD). However, the question remains whether the deficit is in the left or right hemisphere. It is well-recognized that research on patients is vulnerable to comorbidities involved in clinical ADHD and medical history variability. Therefore, the present study applied the dimensional approach to test the relationship between BL in a non-clinical healthy adults and self-reported ADHD symptoms. Eighty-five right handed university students filled in the Conners’ Adult ADHD Rating Scales (CAARS) and performed a BL task. In the task, participants matched a single target letter (verbal processing) or shape (non-verbal processing) displayed below the fixation cross on either left or right visual field with one of two letters or shapes displayed above the fixation cross one on each visual field. BL was indexed as the difference in mean reaction time and error performance between left and right visual field. Multivariable regression analyses showed that BL index calculated from error performance is associated with self-reported ADHD and mood symptoms. The comparison between participants with high and low score on DSM-IV subscales of the CAARS indicated that participants with high scores especially on the hyperactive-impulsive symptoms subscale showed less efficient right hemisphere processing. Findings from non-clinical adults support the dimensionality of right hemisphere deficit and/or high lateralized verbal processing to the left hemisphere in ADHD.