Interindividual variability of the modulatory effects of repetitive transcranial magnetic stimulation on cortical excitability

Abstract

Repetitive transcranial magnetic stimulation (rTMS) appears to have effects on cortical excitability that extend beyond the train of rTMS itself. These effects may be inhibitory or facilitatory and appear to depend on the frequency, intensity, duration and intertrain interval of the rTMS. Many studies assume facilitatory effects of high-frequency rTMS and inhibitory effects of low-frequency rTMS. Nevertheless, the interindividual variability of this modulation of cortical excitability by rTMS has not been systematically investigated. In this study, we applied 240 pulses of rTMS at 90% of the subjects' motor threshold to their motor cortex at different frequencies (1, 10, 15 and 20 Hz) and examined the effects on motor evoked potentials (frequency tuning curve). Although the averaged group data showed a frequency-dependent increase in cortical excitability, each subject had a different pattern of frequency tuning curve, i.e. a different modulatory effect on cortical excitability at different rTMS frequencies. The interindividual variability of these modulatory effects was still high, though less so, when the number of rTMS pulses was increased to 1,600. These findings illustrate the degree of variability of the rTMS effects in the human brain.

Release of premotor activity after repetitive transcranial magnetic stimulation of prefrontal cortex

“…Generally, rTMS was not expected to suppress the function of the targeted brain region, but rather to modulate its activity to a certain degree, by approximately 15 or 20% if consistent with the findings of similar protocols on cortico-spinal excitability Maeda, Keenan, Tormos, Topka, & Pascual-Leone, 2000a;Romero, Anschel, Sparing, Gangitano, & PREMOTOR ACTIVITY AFTER rTMS 299 Pascual- . In this sense rTMS effects on PFC can be conceived as the result of the ''dynamic'' modulation of multiple afferences and efferences in a complex neuronal network (Mottaghy et al, 2000).…”

Transcranial direct current stimulation (tDCS) priming of 1Hz repetitive transcranial magnetic stimulation (rTMS) modulates experimental pain thresholds

“…Stimulation of M1 with low frequency rTMS (1 Hz or less) is associated with decreased cortical excitability, whereas higher frequencies (20-50 Hz) have been associated with an increase in excitability [14].…”

Repetitive transcranial magnetic stimulation of the dorsolateral prefrontal cortex enhances working memory

“…For example, motor cortex appears to be less excitable following stimulation at lower rTMS frequencies, in the 1 Hz range, and more excitable following stimulation by 10 Hz trains (Pascual-Leone and Hallett 1994). The lasting modulatory effects of rTMS have been extensively demonstrated (Maeda et al 2000;Tegenthoff et al 2005;Fregni and Pascual-Leone 2007;Brunoni and Vanderhasselt 2014) and make it a suitable methodological choice for WM enhancement studies (Esslinger et al 2014;Brunoni & Vanderhasselt 2014;Gaudeau-Bosma et al 2013;Guse et al 2013).…”