Forearm and Hand Muscles Exhibit High Coactivation and Overlapping of Cortical Motor Representations

Most of the motor mapping procedures using navigated transcranial magnetic stimulation (nTMS) follow the conventional somatotopic organization of the primary motor cortex (M1) by assessing the representation of a particular target muscle, disregarding the possible coactivation of synergistic muscles. In turn, multiple reports describe a functional organization of the M1 with an overlapping among motor representations acting together to execute movements. In this context, the overlap degree among cortical representations of synergistic hand and forearm muscles remains an open question. This study aimed to evaluate the muscle coactivation and representation overlapping common to the grasping movement and its dependence on the stimulation parameters. The nTMS motor maps were obtained from one carpal muscle and two intrinsic hand muscles during rest. We quantified the overlapping motor maps in size (area and volume overlap degree) and topography (similarity and centroid Euclidean distance) parameters. We demonstrated that these muscle representations are highly overlapped and similar in shape. The overlap degrees involving the forearm muscle were significantly higher than only among the intrinsic hand muscles. Moreover, the stimulation intensity had a stronger effect on the size compared to the topography parameters. Our study contributes to a more detailed cortical motor representation towards a synergistic, functional arrangement of M1. Understanding the muscle group coactivation may provide more accurate motor maps when delineating the eloquent brain tissue during pre-surgical planning.

Description

| openaire: EC/H2020/810377/EU//ConnectToBrain Funding Information: Open Access funding provided by Aalto University. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. VHS received funding from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq; Grant # 140787/2014–3), the Jane & Aatos Erkko Foundation, the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant # 810377), and from the Academy of Finland (Grant # 307963). GPT received a scholarship from CNPq (Grant # 144216/2018–3) and from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP; Grant # 2018/11853–8). OB is funded by FAPESP (Grant # 2013/07699–0) and CNPq (Grant # 304107/2019). RHM is funded by CNPq (Grant # 141056/2018-5). MN and PN were partly supported by RFBR (Grant # 20–315-70048). Publisher Copyright: © 2022, The Author(s).

Keywords

Motor evoked potential, Motor mapping, Neuronavigation, Synergy, TMS, Transcranial magnetic stimulation

DOI

10.1007/s10548-022-00893-1

Citation

Tardelli , G P , Souza , V H , Matsuda , R H , Garcia , M A C , Novikov , P A , Nazarova , M A & Baffa , O 2022 , ' Forearm and Hand Muscles Exhibit High Coactivation and Overlapping of Cortical Motor Representations ' , Brain Topography , vol. 35 , no. 3 , pp. 322-336 . https://doi.org/10.1007/s10548-022-00893-1

Permanent link to this item

https://urn.fi/URN:NBN:fi:aalto-202203282663

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[article-cris] Perustieteiden korkeakoulu / SCI

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