Limited evidence for validity and reliability of non-navigated low and high frequency rTMS over the motor cortex

The neuromodulatory effects of repetitive transcranial magnetic stimulation (rTMS) are often described as inhibiting for low frequency and facilitating for high frequency protocols, leading to the lofi-hife heuristic. However, the data basis for this is inconsistent and reliability of rTMS is barely evaluated. The present study examines the validity of this lofi-hife heuristic at group and single subject level and the reliability of rTMS in a non-navigated setting close to clinical application. In 30 healthy participants, 1 Hz and 20 Hz rTMS were each administered twice over the left motor cortex resulting in four sessions/participant. Motor evoked potentials (MEPs) were measured before and after each session. Reliability measures were intraclass and Pearsons correlation coefficient (ICC and r). The heuristic was not evident at group level. At single-subject level four participants responded with heuristic-conform changes, i.e., concomitant decreases for 1 Hz and increases for 20 Hz sessions. ICCs and r were low to moderate. Within subgroups of less confounded measures, we found good r values for 20 Hz rTMS. Results demonstrate high inter- and intraindividual variability of rTMS questioning the lofi-hife heuristic. Methodological improvements for the usage of rTMS might help to increase validity and reliability of non-invasive brain stimulation.