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68th Annual Meeting of the German Society of Neurosurgery (DGNC)
7th Joint Meeting with the British Neurosurgical Society (SBNS)

German Society of Neurosurgery (DGNC)

14 - 17 May 2017, Magdeburg

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Disentangling the role of the primary motor cortex and the supplementary motor area on force control by short bouts of rTMS

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  • Lasse Wiesinger - Department of Neurosurgery, Eberhard Karls University of Tübingen, Tübingen, Deutschland
  • Marcos Tatagiba - Department of Neurosurgery, Eberhard Karls University of Tübingen, Tübingen, Deutschland
  • Georgios Naros - Department of Neurosurgery, Eberhard Karls University of Tübingen, Tübingen, Deutschland

Deutsche Gesellschaft für Neurochirurgie. Society of British Neurological Surgeons. 68. Jahrestagung der Deutschen Gesellschaft für Neurochirurgie (DGNC), 7. Joint Meeting mit der Society of British Neurological Surgeons (SBNS). Magdeburg, 14.-17.05.2017. Düsseldorf: German Medical Science GMS Publishing House; 2017. DocMi.09.07

doi: 10.3205/17dgnc426, urn:nbn:de:0183-17dgnc4268

Published: June 9, 2017

© 2017 Wiesinger et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at http://creativecommons.org/licenses/by/4.0/.

Outline

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Objective: Tumors in motor eloquent brain regions are frequently associated with a partial loss of contralateral voluntary movements. Furthermore, neurosurgical removal of these tumors carries the risk of amplifying the deficits. Surgical interventions in the primary motor cortex (M1) are associated with a weakness of the voluntary movement, i.e. paresis. In contrast, tumor removal in the supplementary motor area (SMA) causes an akinesia (i.e. SMA syndrome) attributed to a disturbance of motor planning and execution. However, the exact contribution of the M1 and SMA to force control is not well understood. The present study aimed to evaluate the effects of temporary perturbation of M1/SMA function by short bouts of rTMS on contralateral force output.

Methods: Eleven healthy, right-handed subjects were enrolled in the present study. The task consisted of abduction movements of the right thumb connected to a custom-made manipulandum. After determining the individual resting motor threshold (rMT) of the Abductor pollicis brevis muscle (ABP) and its maximum force output (MFO), subjects were asked to apply six different target force (TF) levels indicated by visual cues. Feedback of the current force output was provided on a screen. Just prior to the visual cue, rTMS (2 s, 5 Hz, 90% rMT) was randomly applied either to M1 or to SMA, causing transient virtual lesioning. Several task parameters, i.e. reaction time (RT), time to target force (TTF), scaling error (SE) and target force error (TFE), were analyzed and compared to trials with sham rTMS.

Results: rTMS to the SMA resulted in a significant reduction of RTs independent of the TF. However, there were no significant effects on TTF by any rTMS protocol. While there was positive TFE for lower TF levels (i.e. overshooting), rTMS of the SMA resulted in a negative TFE (i.e. undershooting) in trials with high TF levels. In contrast, there was a reduced force output after rTMS to M1 independent of the TF. Finally, SE was increased only after rTMS to the SMA.

Conclusion: Transient virtual lesioning of SMA was associated with an impairment of force scaling during trials with lower force levels. In contrast, there was no impairment of force scaling after rTMS to M1; however, transient virtual lesioning of M1 revealed a reduction of maximum force output. The present study suggests an involvement of left SMA in force control of the contralateral hand providing further insights in the pathophysiology of the postoperative SMA syndrome.