Stability and test-retest reliability of neuronavigated TMS measures of corticospinal and intracortical excitability.

The present study aimed at investigating the long-term stability and test-retest reliability of neuronavigated transcranial magnetic stimulation (nTMS) measures of cortical excitability, inhibition, and facilitation in the primary motor cortex. To fulfill these aims, thirty-one healthy adults underwent four nTMS sessions, over an average one-month period. Stability and test-retest reliability statistics were computed and analyzed to produce smallest real difference statistics, which indicate the absolute variation in a measurement that is likely to be the result of error (randomness). Excellent reliability was found for resting motor thresholds, which reflect baseline neuronal excitability. Good reliability statistics were found for input/output curve measurements, which reflect the excitability of a highly plastic neuronal population. Using the slope of mean amplitudes throughout the input/output curve or the stimulator intensity required to elicit motor evoked potentials of 1 mV presented good to excellent measurement reliability for global cortical excitability indexing, compared to mean MEP at a given intensity. Overall, this methodological study provides useful and novel information on transcranial magnetic stimulation interventions by providing smallest real difference statistics that inform on potential response thresholds across time, contributing to the validation of these measurements as clinical monitoring tools across time.