title: Differential modulation of motor network connectivity during movements of the upper and lower limbs.
abstract: Voluntary movements depend on a well-regulated interplay between the primary motor cortex (M1) and premotor areas. While to date the neural underpinnings of hand movements are relatively well understood, we only have rather limited knowledge on the cortical control of lower-limb movements. Given that our hands and feet have different roles for activities of daily living, with hand movements being more frequently used in a lateralized fashion, we hypothesized that such behavioral differences also impact onto network dynamics underlying upper and lower limb movements. We, therefore, used functional magnetic resonance imaging (fMRI) and dynamic causal modeling (DCM) to investigate differences in effective connectivity underlying isolated movements of the hands or feet in 16 healthy subjects. The connectivity analyses revealed that both movements of the hand and feet were accompanied by strong facilitatory coupling of the respective contralateral M1 representations with premotor areas of both hemispheres. However, excitatory influences were significantly lower for movements of the feet compared to hand movements. During hand movements, the M1(hand) representation ipsilateral to the movement was strongly inhibited by premotor regions and the contralateral M1 homologue. In contrast, interhemispheric inhibition was absent between the M1(foot) representations during foot movements. Furthermore, M1(foot) ipsilateral to the moving foot exerted promoting influences onto contralateral M1(foot). In conclusion, the generally stronger and more lateralized coupling pattern associated with hand movements suggests distinct fine-tuning of cortical control to underlie voluntary movements with the upper compared to the lower limb.
authors.affiliation: Department of Neurology, University of Cologne, Germany; Department of Psychological and Brain Sciences, University of California, Santa Barbara, USA; Neuromodulation & Neurorehabilitation, Max Planck Institute for Neurological Research, Cologne, Germany.
authors.forename: Lukas J
authors.initials: LJ
authors.lastname: Volz
authors.affiliation: Institute of Neuroscience and Medicine (INM-1, INM-3), Juelich Research Centre, Germany; Institute for Clinical Neuroscience and Medical Psychology, Heinrich-Heine University, Düsseldorf, Germany.
authors.forename: Simon B
authors.initials: SB
authors.lastname: Eickhoff
authors.affiliation: Neuromodulation & Neurorehabilitation, Max Planck Institute for Neurological Research, Cologne, Germany; Institute of Neuroscience and Medicine (INM-1, INM-3), Juelich Research Centre, Germany.
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Pool
authors.affiliation: Department of Neurology, University of Cologne, Germany; Institute of Neuroscience and Medicine (INM-1, INM-3), Juelich Research Centre, Germany.
authors.forename: Gereon R
authors.initials: GR
authors.lastname: Fink
authors.affiliation: Department of Neurology, University of Cologne, Germany; Neuromodulation & Neurorehabilitation, Max Planck Institute for Neurological Research, Cologne, Germany; Institute of Neuroscience and Medicine (INM-1, INM-3), Juelich Research Centre, Germany. Electronic address: christian.grefkes@uk-koeln.de.
authors.forename: Christian
authors.initials: C
authors.lastname: Grefkes
mesh_terms: D000328:Adult; D001499:Bayes Theorem; D001931:Brain Mapping; D005260:Female; D005528:Foot / Q000502:physiology*; D007839:Functional Laterality; D006225:Hand / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009068:Movement; D009415:Nerve Net / Q000502:physiology; D055815:Young Adult