title: Ascending beta oscillation from finger muscle to sensorimotor cortex contributes to enhanced steady-state isometric contraction in humans.
abstract: OBJECTIVE
  β-Band corticomuscular coherence is suggested as an electrophysiological mechanism that contributes to sensorimotor functioning in the maintenance of steady-state contractions. Converging evidence suggests that not only the descending corticospinal pathway but the ascending sensory feedback pathway is involved in the generation of β-band corticomuscular coherence. The present study aimed to investigate which pathway, descending vs. ascending, contributes more to the stability of muscle contraction, especially for human intrinsic hand muscles.
  
  
  METHODS
  In this study, we assessed directed transfer function (DTF) between magnetoencephalography signals over the sensorimotor cortex (SMC) and rectified electromyographic (EMG) signals recorded during steady-state isometric contraction of the right thumb muscle (flexor pollicis brevis, FPB) or right little finger muscle (flexor digiti minimi brevis, FDMB) in 15 right-handed healthy subjects.
  
  
  RESULTS
  β-Band DTF was statistically significant in both descending (SMC→EMG) and ascending (EMG→SMC) directions, and mean phase delays for each direction were in agreement with the conduction time for the descending corticospinal and ascending sensory feedback pathways. The strengths of the β-band DTF (EMG→SMC direction) were greater in the FPB muscle than in the FDMB muscle, while the strengths of the β-band DTF (SMC→EMG direction) were not different between the two muscles. Moreover, the β-band DTF (EMG→SMC direction) was greater in the "Stable" period than in the "Less Stable" period within the FDMB muscle. Greater DTF (EMG→SMC direction) was positively associated with the stability of muscle contraction.
  
  
  CONCLUSIONS
  Our findings suggest that ascending β-band oscillatory activity may promote a steady-state isometric contraction by efficiently transmitting sensory feedback from finger muscles to the sensorimotor cortex.
  
  
  CONCLUSIONS
  The results show the differential contribution of the ascending part of the corticomuscular network depending on the functional organization.
authors.affiliation: Interdisciplinary Program in Neuroscience, Seoul National University College of Natural Sciences, 151-742 Seoul, South Korea; MEG Center, Department of Neurosurgery, Seoul National University Hospital, 110-744 Seoul, South Korea.
authors.forename: Manyoel
authors.initials: M
authors.lastname: Lim
authors.affiliation: MEG Center, Department of Neurosurgery, Seoul National University Hospital, 110-744 Seoul, South Korea; Sensory Organ Research Institute, Seoul National University Medical Research Center, 110-744 Seoul, South Korea.
authors.forename: June Sic
authors.initials: JS
authors.lastname: Kim
authors.affiliation: MEG Center, Department of Neurosurgery, Seoul National University Hospital, 110-744 Seoul, South Korea.
authors.forename: Minaeh
authors.initials: M
authors.lastname: Kim
authors.affiliation: Interdisciplinary Program in Neuroscience, Seoul National University College of Natural Sciences, 151-742 Seoul, South Korea; MEG Center, Department of Neurosurgery, Seoul National University Hospital, 110-744 Seoul, South Korea; Department of Brain and Cognitive Sciences, Seoul National University College of Natural Sciences, 151-742 Seoul, South Korea. Electronic address: chungc@snu.ac.kr.
authors.forename: Chun Kee
authors.initials: CK
authors.lastname: Chung
mesh_terms: D000328:Adult; D001611:Beta Rhythm / Q000502:physiology*; D004576:Electromyography / Q000379:methods; D005260:Female; D005385:Fingers / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D015225:Magnetoencephalography / Q000379:methods; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D066191:Sensorimotor Cortex / Q000502:physiology*; D013933:Thumb / Q000502:physiology; D055815:Young Adult
keywords: Beta oscillation; Corticomuscular coherence; Magnetoencephalography; Sensorimotor cortex