Abstract
During the last decade, repetitive transcranial magnetic stimulation (rTMS) of the prefrontal cortex has become established as a treatment for various mental diseases. The rational of prefrontal stimulation has been adapted from the mode of action known from rTMS using motor-evoked potentials though little is known about the precise effect of rTMS at prefrontal sites. The objective of the current study is to investigate the inhibitory effect of prefrontal 1 Hz rTMS by stimulating the generators of event-related potentials (ERP) which are located in the prefrontal cortex. Thus, 1 Hz rTMS was applied offline over the left dorsolateral prefrontal cortex (DLPFC) and the medial prefrontal cortex (MPFC) in 18 healthy subjects who subsequently underwent a GoNogo task. Both active conditions were compared to sham rTMS within a randomized and counterbalanced cross-over design in one day. ERPs were recorded during task performance and the N2 and the P3 were analysed. After 1 Hz rTMS of the left DLPFC (but not of the MPFC), an inhibitory effect on the N2 amplitude was observed, which was related to inhibitory control. In contrast, after 1 Hz rTMS of the MPFC (but not at the left DLPFC) a trend towards an increased P3 amplitude was found. There was no significant modulation of latencies and behavioural data. The results argue in favour of an inhibitory effect of 1 Hz rTMS on N2 amplitudes in a GoNogo task. Our findings suggest that rTMS may mildly modulate prefrontally generated ERP immediately after stimulation, even where behavioural effects are not measurable. Thus, combined rTMS-ERP approaches need to be further established in order to serve as paradigms in experimental neuroscience and clinical research.
Highlights
During the last decade, prefrontal repetitive transcranial magnetic stimulation has become increasingly established as a treatment for various mental diseases
Neural oscillations which can be directly measured comparable to motor-evoked potentials (MEP) of repetitive transcranial magnetic stimulation (rTMS) at motor sites – such as event-related potentials (ERPs) – are a promising tool to estimate the mode of action of prefrontal rTMS
The statistical trend concerning the contrast between medial prefrontal cortex (MPFC) rTMS and sham control could not be detected in further threefactorial analysis and was not visible in the grand average
Summary
Prefrontal repetitive transcranial magnetic stimulation (rTMS) has become increasingly established as a treatment for various mental diseases. For this purpose the rationale of stimulation has been adapted from the mode of action known from motor-evoked potentials (MEP). Some imaging studies of prefrontal 1 Hz rTMS have been conducted showing decreasing [9] or increasing metabolism [10]. These contradictory results are attributed to indirect transsynaptical rTMS effects combined with brain activity measurements which are mediated by metabolism. Neural oscillations which can be directly measured comparable to MEPs of rTMS at motor sites – such as event-related potentials (ERPs) – are a promising tool to estimate the mode of action of prefrontal rTMS
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