Introduction: The electroencephalographic response following transcranial magnetic stimulation after 100 ms (TMS-evoked N100) is of special interest for the investigation of cortical inhibitory deficits in Attention Deficit Hyperactivity Disorder (ADHD). In healthy subjects, the TMS-evoked N100 decreases during motor response preparation and movement execution and increases during response inhibition. The aim of this study is to investigate the modulation of TMS-evoked N100 at stages of response preparation, activation, execution and inhibition in ADHD patients during a go/nogo task.

Methods: 18 children with ADHD and 19 typically developing children, aged 10 to 14 years, all right handed were assessed. TMS was delivered over the left motor cortex, the TMS-N100 was measured at electrode P3. The TMS-evoked N100 was determined at rest and at different time points (50 ms before S2; 150, 300 and 500 ms after S2) in a cued go/nogo task (S1-S2 paradigm).

Results: Though the TMS-evoked N100 was not found to be significantly reduced at rest in the ADHD group, a smaller increase in go trials and a smaller decrease after inhibiting a response compared to typically developing children were observed. In go trials, a lower TMS-evoked N100 was associated with a smaller variability of reaction times.

Conclusion: A reduced modulation of the TMS-evoked N100 amplitude at response execution and inhibition during a go/nogo task, extends the picture of inhibition deficits at the cortical level in ADHD underlining the relevance of the TMS-evoked N100.