title: Bringing transcranial mapping into shape: Sulcus-aligned mapping captures motor somatotopy in human primary motor hand area.
abstract: Motor representations express some degree of somatotopy in human primary motor hand area (M1HAND), but within-M1HAND corticomotor somatotopy has been difficult to study with transcranial magnetic stimulation (TMS). Here we introduce a "linear" TMS mapping approach based on the individual shape of the central sulcus to obtain mediolateral corticomotor excitability profiles of the abductor digiti minimi (ADM) and first dorsal interosseus (FDI) muscles. In thirteen young volunteers, we used stereotactic neuronavigation to stimulate the right M1HAND with a small eight-shaped coil at 120% of FDI resting motor threshold. We pseudorandomly stimulated six targets located on a straight mediolateral line corresponding to the overall orientation of the central sulcus with a fixed coil orientation of 45° to the mid-sagittal line (STRAIGHT-450FIX) or seven targets in the posterior part of the crown of the central sulcus following the bending of the central sulcus (CURVED). CURVED mapping employed a fixed (CURVED-450FIX) or flexible coil orientation producing always a current perpendicular to the sulcal wall (CURVED-900FLEX). During relaxation, CURVED but not STRAIGHT mapping revealed distinct corticomotor excitability peaks in M1HAND with the excitability maximum of ADM located medially to the FDI maximum. This mediolateral somatotopy was still present during tonic contraction of the ADM or FDI. During ADM contraction, cross-correlation between the spatial excitability profiles of ADM and FDI was lowest for CURVED-900FLEX. Together, the results show that within-M1HAND somatotopy can be readily probed with linear TMS mapping aligned to the sulcal shape. Sulcus-aligned linear mapping will benefit non-invasive studies of representational plasticity in human M1HAND.
authors.affiliation: Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Denmark; Fonctions Cérébrales et Neuromodulation, Université Joseph Fourier, Grenoble, France; Inserm, U836, Grenoble Institut des Neurosciences, Grenoble, France. Electronic address: estelle.raffin@ujf-grenoble.fr.
authors.forename: Estelle
authors.initials: E
authors.lastname: Raffin
authors.affiliation: Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Denmark; Department of Neurology, Campus Bio-Medico University of Rome, Rome, Italy; Multimodal Functional Imaging Laboratory Montreal Neurological Institute, McGill University, Montreal, QC, Canada.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Pellegrino
authors.affiliation: Department of Neurology, Campus Bio-Medico University of Rome, Rome, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Di Lazzaro
authors.affiliation: Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Denmark; Technical University of Denmark, Department of Electrical Engineering, Biomedical Engineering Section, Kgs. Lyngby, Denmark.
authors.forename: Axel
authors.initials: A
authors.lastname: Thielscher
authors.affiliation: Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Denmark; Department of Neurology, Copenhagen University Hospital Bispebjerg, Copenhagen, Denmark.
authors.forename: Hartwig Roman
authors.initials: HR
authors.lastname: Siebner
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006225:Hand / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D038361:Neuronavigation; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult