Hyperactivity in ADHD may be a compensation mechanism rather than a core symptom

May 21st, 2015

A US study has found that hyperactivity in children with ADHD may be a compensation mechanism to help neurocognitive functioning, rather than a core deficit contributing to impairments.

Researchers at the Center for Advancement of Youth in Jackson, Mississippi, compared 29 8–12-year-old boys diagnosed with ADHD with 23 typically developing boys of the same age. Children were assessed for phonological working memory, attentive behaviour and gross motor activity during tasks across four weekly sessions.

Higher rates of motor activity in the ADHD group predicted significantly better, although not normalised, performance on phonological working memory tasks. In contrast, high activity levels in the typically developing group predicted lower performance. Individual children in the ADHD group were also more likely to be categorised as ‘improved’ in working memory tasks at the highest observed activity level and ‘deteriorated’ at the lowest activity level.

The authors suggest that these results may be due to an ‘inverted U’ relationship between arousal and cognitive performance; a certain amount of cortical arousal is beneficial for performance. Under-aroused children with ADHD may compensate and increase cortical arousal by increasing their physical activity. For children with adequate levels of arousal, excessive physical movement can lead to over-arousal and a consequent decrease in cognitive performance.

The researchers conclude that further work on larger samples that include girls, older/younger children, and those with different clinical presentations of ADHD, may help to assess whether these results can be generalised to children with ADHD. It could also determine whether classroom interventions that incorporate movement while remaining seated might improve academic performance for these children. Importantly, although the ADHD group overall showed improved performance with increased activity levels, 17% had worse performance when their activity levels increased, suggesting that activity-based interventions may not be helpful for all children with ADHD. In addition, further research is needed to determine whether visuospatial, as well as phonological working memory, is affected by activity levels in children with ADHD.

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