The myelin content of the human precentral hand knob reflects inter-individual differences in manual motor control at the physiological and behavioural level

Raffaele Dubbioso*, Kristoffer Hougaard Madsen, Axel Thielscher, Hartwig Roman Siebner

*Corresponding author for this work

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The primary motor hand area (M1HAND) and adjacent dorsal premotor cortex (PMd) form the so-called motor hand knob in the precentral gyrus. M1HAND and PMd are critical for dexterous hand use and are densely inter-connected via cortico-cortical axons, lacking a sharp demarcating border. In 24 young right-handed volunteers, we performed multi-modal mapping to delineate the relationship between structure and function in the right motor hand knob. Quantitative structural magnetic resonance imaging (MRI) at 3 Tesla yielded regional R1-maps as a proxy of cortical myelin content. Participants also underwent functional MRI. We mapped task-related activation and temporal precision, while they performed a visuo-motor synchronization task requiring visually cued abduction movements with the left index or little finger. We also performed sulcus-aligned transcranial magnetic stimulation (TMS) of the motor hand knob to localize the optimal site (hotspot) for evoking a motor evoked potential (MEP) in two intrinsic hand muscle. Individual motor hotspot locations varied along the rostro-caudal axis. The more rostral the motor hotspot location in the precentral crown, the longer were corticomotor MEP latencies. "Hotspot rostrality" was associated with the regional myelin content in the precentral hand knob. Cortical myelin content also correlated positively with task-related activation of the precentral crown and temporal precision during the visuo-motor synchronization task. Together, our results suggest a link between cortical myelination, the spatial cortical representation and temporal precision of finger movements. We hypothesize that the myelination of cortical axons facilitates neuronal integration in PMd and M1HAND and hereby, promotes the precise timing of movements.SIGNIFICANCE STATEMENTHere we used magnetic resonance imaging and transcranial magnetic stimulation (TMS) of the precentral motor hand knob to test for a link between cortical myelin content, functional cortico-motor representations, and manual motor control. A higher myelin content of the precentral motor hand knob was associated with more rostral corticomotor presentations, with stronger task-related activation and a higher precision of movement timing during a visuo-motor synchronization task. We propose that a high precentral myelin content enables fast and precise neuronal integration in M1 and PMd, resulting in higher temporal precision during dexterous hand use. Our results identify the degree of myelination as an important structural feature of the neocortex that is tightly linked to the function and behaviour supported by the cortical area.
Original languageEnglish
JournalJournal of neuroscience
Number of pages53
Publication statusAccepted/In press - 2021


  • Motor skill
  • Premotor cortex
  • Primary motor cortex
  • Functional cortical mapping
  • Magnetic resonance imaging

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