Differential task-related fMRI effects of a single dose of guanfacine and lisdexamfetamine in youth with ADHD: a randomised, double-blind, placebo-controlled crossover study

Background: Stimulant and non-stimulant medications increase fronto-striato-thalamic activation in youth with Attention-Deficit/Hyperactivity Disorder (ADHD). However, comparative effects of the more recently licensed stimulant lisdexamfetamine and non-stimulant guanfacine on functional magnetic resonance imaging (fMRI) correlates in ADHD are unknown. Methods: This exploratory randomised, placebo-controlled, double-blind, crossover study compared fMRI activation in youth with ADHD during a tracking stop-signal task (SST; N = 12), a working memory task (N-back; N = 11) and a sustained attention task (SAT; N = 10), after single clinical doses of either guanfacine extended-release, lisdexamfetamine, or placebo, with one-week washouts. Twenty-one demographically matched typically developing controls (TD) were assessed once to test for potential normalisation of case-control activation differences. Results: Region of interest analysis showed increased right caudate and putamen activation for lisdexamfetamine versus placebo during N-back and SAT, respectively. Both drugs shared an increase in left superior temporal activation versus placebo during N-back. In whole-brain analyses only lisdexamfetamine increased precuneus/posterior cingulate activation during SST versus guanfacine, and during N-back in pre- and postcentral and occipital cortices versus placebo. During SST, placebo-treated ADHD versus TD showed reduced putamen, insula, parietal and occipital activation that was potentially attenuated/normalised under lisdexamfetamine, while under guanfacine lingual gyrus underactivation remained, with additional precuneus and middle temporal underactivation. Also, only lisdexamfetamine improved and normalised SST performance. Conclusion: Lisdexamfetamine appears to have stronger and drug-exclusive upregulation and potential attenuation/normalisation effects than guanfacine on basal ganglia, posterior parieto-occipital and sensorimotor activations during ADHD-relevant executive function tasks with some shared putamen and superior temporal effects.