The reliability and validity of rapid transcranial magnetic stimulation mapping

Background: Traditional transcranial magnetic stimulation mapping involves systematically delivering stimuli over a predefined grid. The pseudorandom walk method seeks to improve map acquisition times by abandoning the grid in favour of delivering stimuli randomly over a given area. Objectives: To i) determine the minimum interstimulus interval (ISI) required for reliable mapping outcomes within and between sessions using the pseudorandom walk method and ii) assess the validity of the pseudorandom walk method by testing its equivalence with traditional mapping. Methods: Maps collected using the pseudorandom walk method at four ISIs (4, 3, 2, and 1s) were compared to maps collected using traditional mapping in twenty healthy individuals. Outcomes included map area, volume, centre of gravity, mean MEP amplitude, and number of discrete peaks. Results and Conclusions: The pseudorandom walk method was valid and reliable with a 2-second ISI for all outcomes except number of discrete peaks, which was less reliable than other measures.