Klinische Neurophysiologie 2012; 43 - V029
DOI: 10.1055/s-0032-1301445

Virtual Lesion-induced Rapid Reorganization in the Working Memory Network in Multiple Sclerosis

OL Gamboa Arana 1, M Wahl 1, S Borisov 1, E Tagliazucchi 2, H Laufs 2, U Ziemann 1
  • 1Universitätsklinikum Frankfurt am Main, Klinik für Neurologie, Frankfurt am Main
  • 2Brain Imaging Center Frankfurt, Frankfurt am Main

Background: Multiple sclerosis (MS) patients at the early stage of the disease typically show normal working memory (WM) performance. However, studies with fMRI revealed increased BOLD activity and altered connectivity in nodes of the WM network (e.g. BA9, BA46) in MS patients [1, 2]. It remains unclear if the observed changes represent compensatory mechanisms.

Methods: To clarify this, we used continuous theta burst stimulation (cTBS) to create a virtual lesion in the right BA9 prior to behavioural experiments. Early stage MS patients (CIS or RRMS, EDSS ≤ 2.0, T2-lesion volume < 2mL; n=5) and healthy controls (n=8) performed a block design WM task (PASAT–3) during functional MRI. As a control for cTBS effect specificity, sham stimulation was performed in all subjects.

Results: Our results confirmed increased task-related BOLD activation in several nodes of the WM network in patients (e.g. BA9, BA6). CTBS had no detrimental effect on WM performance. Moreover, after applying cTBS on lateral BA9, MS patients showed increased BOLD activity in a medial part of the same area (right BA9). Functional connectivity (FC) analyses at baseline show increased connectivity between the stimulation site and bilateral medial BA9 subregions in MS patients.

Conclusions: Findings indicate virtual lesion-induced rapid reorganisation of the WM network in MS patients which is likely compensatory to maintain WM function. Increased baseline functional connectivity might provide a predictor for this compensatory capacity of the brain.

Literatur: 1. Au Duong, M.V., et al., Modulation of effective connectivity inside the working memory network in patients at the earliest stage of multiple sclerosis. Neuroimage, 2005. 24(2): p. 533-8. 2. Audoin, B., et al., Magnetic resonance study of the influence of tissue damage and cortical reorganization on PASAT performance at the earliest stage of multiple sclerosis. Hum Brain Mapp, 2005. 24(3): p. 216-28.