title: A critical period of corticomuscular and EMG-EMG coherence detection in healthy infants aged 9-25 weeks.
abstract: The early postnatal development of functional corticospinal connections in human infants is not fully clarified. Corticospinal drive to upper and lower limb muscle shows developmental changes with an increased functional coupling in infants between 9 and 25 weeks in the beta frequency band. The changes in functional coupling coincide with the developmental period where fidgety movements are present in healthy infants. Data support a possible sensitive period where functional connections between corticospinal tract fibres and spinal motoneurones undergo activity-dependent reorganization.
  
  
  
  The early postnatal development of functional corticospinal connections in human infants is not fully clarified. We used EEG and EMG to investigate the development of corticomuscular and intramuscular coherence as indicators of functional corticospinal connectivity in healthy infants aged 1-66 weeks. EEG was recorded over leg and hand area of motor cortex. EMG recordings were made from right ankle dorsiflexor and right wrist extensor muscles. Quantification of the amount of corticomuscular coherence in the 20-40 Hz frequency band showed a significantly larger coherence for infants aged 9-25 weeks compared to younger and older infants. Coherence between paired EMG recordings from tibialis anterior muscle in the 20-40 Hz frequency band was also significantly larger for the 9-25 week age group. A low-amplitude, broad-duration (40-50 ms) central peak of EMG-EMG synchronization was observed for infants younger than 9 weeks, whereas a short-lasting (10-20 ms) central peak was observed for EMG-EMG synchronization in older infants. This peak was largest for infants aged 9-25 weeks. These data suggest that the corticospinal drive to lower and upper limb muscles shows significant developmental changes with an increase in functional coupling in infants aged 9-25 weeks, a period which coincides partly with the developmental period of normal fidgety movements. We propose that these neurophysiological findings may reflect the existence of a sensitive period where the functional connections between corticospinal tract fibres and spinal motoneurones undergo activity-dependent reorganization. This may be relevant for the timing of early therapy interventions in infants with pre- and perinatal brain injury.
authors.affiliation: Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark.|Elsass Institute, Charlottenlund, Denmark.
authors.forename: Anina
authors.identifier: 0000-0002-3154-2537
authors.initials: A
authors.lastname: Ritterband-Rosenbaum
authors.affiliation: Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark.|Elsass Institute, Charlottenlund, Denmark.|Department of Neonatology, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark.
authors.forename: Anna
authors.initials: A
authors.lastname: Herskind
authors.affiliation: Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Xi
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark.|Elsass Institute, Charlottenlund, Denmark.
authors.forename: Maria
authors.initials: M
authors.lastname: Willerslev-Olsen
authors.affiliation: Elsass Institute, Charlottenlund, Denmark.|Applied Mathematics and Computer Science, Technical University of Denmark, Kgs. Lyngby, Denmark.
authors.forename: Mikkel Damgaard
authors.initials: MD
authors.lastname: Olsen
authors.affiliation: Sobell Department of Motor Neuroscience & Movement Disorders, Institute of Neurology, University College London & Department of Clinical Neurology, National Hospital for Neurology and Neurosurgery, UK.
authors.forename: Simon Francis
authors.identifier: 0000-0001-5193-8195
authors.initials: SF
authors.lastname: Farmer
authors.affiliation: Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark.|Elsass Institute, Charlottenlund, Denmark.
authors.forename: Jens Bo
authors.identifier: 0000-0001-5568-2916
authors.initials: JB
authors.lastname: Nielsen
mesh_terms: D000367:Age Factors; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009044:Motor Cortex / Q000254:growth & development* / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000254:growth & development* / Q000502:physiology; D011712:Pyramidal Tracts / Q000254:growth & development* / Q000502:physiology
keywords: coherence; development; electroencephalogram (EEG); electromyogram (EMG); fidgety movements; infants