Handedness in ADHD: Meta-Analyses


Meta-analyses have shown that several neurodevelopmental and psychiatric disorders, such as autism spectrum disorder and schizophrenia, are associated with a higher prevalence of left-and/or mixed-handedness. One neurodevelopmental disorder for which this association is unclear is attention deficit hyperactivity disorder (ADHD). Here, some empirical studies have found evidence for a higher prevalence of left-and/or mixed-handedness in individuals with ADHD compared to neurotypical individuals. However, other studies failed to establish such an association. Therefore, meta-analytic integration is critical to estimate whether or not there is an association between handedness and ADHD. We report the results of three meta-analyses comparing handedness in individuals with ADHD to controls (typically developing individuals). The results show no evidence of differences in left-handedness and non-right-handedness between individuals with ADHD and controls. It was, however, found that individuals with ADHD showed a higher prevalence of mixed-handedness than controls. These findings are discussed in the context of the hypothesis that ADHD is a disorder in which mostly right-hemispheric brain networks are affected. Since right-handedness represents a dominance of the left motor cortex for fine motor behavior, such as writing, as well as a left-hemispheric dominance for language functions, and about 90% of individuals are right-handers, this hypothesis might explain why left-handedness is mostly unaffected in ADHD. We suggest that only in conditions where language is affected one should expect to find elevated levels of left łdots