Normative data on changes in transcranial magnetic stimulation measures over a ten hour period

Objective: To establish normative data on the single-subject variation of resting motor thresholds and silent periods over 10 h using transcranial magnetic stimulation (TMS). Methods: Seventeen neurologically normal volunteers aged 18-36 underwent a series of seven TMS sessions conducted over the course of a single 10-h period. During each session, resting motor threshold and cortical silent period were recorded for the first dorsal interosseus muscle of each hand during focal TMS of the contralateral motor area. Results: We provide data on the normal limits of variability in these measures for averaged group data and for single subjects. Specifically, we report intersession, intrasession, and interhemispheric variability of data for each subject individually. Conclusions: Although group averages are highly reliable, individual subjects showed substantial variability over time, especially for silent periods. Interhemispheric asymmetry was a less stable indicator than previously reported. Significance: These norms may guide the interpretation of changes in TMS measures within groups or within an individual patient over brief periods of time or as an immediate response to intervention.