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Neuroimage. 2015 Sep;118:209-18. doi: 10.1016/j.neuroimage.2015.06.004. Epub 2015 Jun 5.

Inter-individual variability in cortical excitability and motor network connectivity following multiple blocks of rTMS.

Author information

1
Institute of Neuroscience and Medicine (INM-1, INM-3), Juelich Research Centre, 52428 Juelich, Germany; Department of Neurology, Cologne University Hospital, 50924 Cologne, Germany.
2
Department of Neurology, Cologne University Hospital, 50924 Cologne, Germany.
3
Institute of Neuroscience and Medicine (INM-1, INM-3), Juelich Research Centre, 52428 Juelich, Germany; Institute of Clinical Neuroscience and Medical Psychology, Heinrich Heine University, 40225 Duesseldorf, Germany.
4
Institute of Neuroscience and Medicine (INM-1, INM-3), Juelich Research Centre, 52428 Juelich, Germany; Department of Neurology, Cologne University Hospital, 50924 Cologne, Germany. Electronic address: Christian.Grefkes@uk-koeln.de.

Abstract

The responsiveness to non-invasive neuromodulation protocols shows high inter-individual variability, the reasons of which remain poorly understood. We here tested whether the response to intermittent theta-burst stimulation (iTBS) - an effective repetitive transcranial magnetic stimulation (rTMS) protocol for increasing cortical excitability - depends on network properties of the cortical motor system. We furthermore investigated whether the responsiveness to iTBS is dose-dependent. To this end, we used a sham-stimulation controlled, single-blinded within-subject design testing for the relationship between iTBS aftereffects and (i) motor-evoked potentials (MEPs) as well as (ii) resting-state functional connectivity (rsFC) in 16 healthy subjects. In each session, three blocks of iTBS were applied, separated by 15min. We found that non-responders (subjects not showing an MEP increase of ≥10% after one iTBS block) featured stronger rsFC between the stimulated primary motor cortex (M1) and premotor areas before stimulation compared to responders. However, only the group of responders showed increases in rsFC and MEPs, while most non-responders remained close to baseline levels after all three blocks of iTBS. Importantly, there was still a large amount of variability in both groups. Our data suggest that responsiveness to iTBS at the local level (i.e., M1 excitability) depends upon the pre-interventional network connectivity of the stimulated region. Of note, increasing iTBS dose did not turn non-responders into responders. The finding that higher levels of pre-interventional connectivity precluded a response to iTBS could reflect a ceiling effect underlying non-responsiveness to iTBS at the systems level.

KEYWORDS:

Cortical plasticity; Dose-dependency; SMA; Variability; dPMC

PMID:
26052083
PMCID:
PMC5216181
DOI:
10.1016/j.neuroimage.2015.06.004
[Indexed for MEDLINE]
Free PMC Article

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