Intracortical motor inhibition and facilitation in adults with attention deficit/hyperactivity disorder

Using transcranial magnetic stimulation (TMS), disturbed facilitatory and inhibitory motor functions were recently found to correlate with motor hyperactivity in children with ADHD. Since hyperactivity seems to become reduced in ADHD during the transition to adulthood, a normalization of motor cortical excitability might be assumed. Therefore, we investigated the same inhibitory and facilitatory TMS paradigms in ADHD adults as we had previously examined in children. Motor cortical excitability was tested with TMS paired-pulse protocols in 21 ADHD adults and 21 age- and gender-matched healthy controls. In contrast to our results in ADHD children, no group-specific differences in amplitude changes of motor evoked potentials for inhibitory inter-stimulus intervals (ISI) (3, 100, 200 and 300 ms) or for facilitatory ISIs (13, 50 ms) could be detected. In ADHD adults, disturbed facilitatory and inhibitory motor circuits as found in ADHD children could not be shown, probably due to a development-dependent normalization of motor cortical excitability.