Restoration of disturbed intracortical motor inhibition and facillitation in attention deficit hyperactivity disorder children by methylphenidate

Background: Previous investigations using transcranial magnetic stimulation (TMS) have shown that neural inhibitory motor circuits are disturbed in ADHD children. We sought to investigate the influence of methylphenidate (MPH) on inhibitory and facilitatory motor circuits of ADHD children with TMS paired pulse protocols using surplus long interval inter-stimulus intervals (ISI) not investigated so far. Methods: Motorcortical modulation was tested with TMS paired pulse protocols employing ISI of 3, 13, 50,100, 200, and 300 msec in 18 ADHD children before! and on treatment with MPH. Clinical improvement by MPH was measured by the Conners score. Results: Analysis of variance (ANOVA) revealed a significant three-way interaction "Group X Amplitude X ISI," p =.001. Subsequent two-factorial ANOVAs and t-tests showed group specific differences of motor evoked potential (MEP) amplitudes for inhibitory ISIs of 3 and 100 msec, and for facilitatory ISIs of 13 and 50 msec. Compared to controls, an adjustment of these parameters by MPH could be shown. On MPH, a significant bivariate correlation was found between the Conners score reduction and averaged MEP amplitude changes only for inhibitory ISIs Q and 100 msec). Conclusions: In ADHD children, MPH modulates disturbed facilitatory and inhibitory motor circuits, which for the latter is associated with clinical improvement.