Reliability of the ‘observation of movement’ method for determining motor threshold using transcranial magnetic stimulation

► The observation of movement (OM) method is used for obtaining motor threshold for the application of transcranial magnetic stimulation. ► We present evidence that verifies the high test/re-test reliability of this method. ► Our findings confirm the suitability of the OM method as a safe and accurate method of assessing cortical excitability. The aim of this study was to establish the reliability of the observation of movement (OM) method for obtaining motor threshold (MT) in transcranial magnetic stimulation (TMS). MTs were obtained on separate days, following separate hunting procedures, for both left and right motor cortex (M1), with one or multiple estimates obtained from the same hemisphere within a single session. MTs obtained using the OM method were highly reliable and reproducible on different days (left M1: r = .98, p < .0001; right M1: r = .97, p < .0001). MTs were not influenced by the order of acquisition when two hemispheres were stimulated in the same session [ F(1,22) = .12, p = .73] or by the collection of additional MTs as part of the distance-adjusted procedure [ F(1,23) = .74, p = .40]. The results verify the reliability of the OM method and confirm its viability for the safe and efficient application of TMS to the left and right M1. The OM method is a reliable technique for obtaining MT and is relatively simple and quick to run. It therefore provides an effective procedure for research and clinical applications.