title: Multiple frequency functional connectivity in the hand somatosensory network: an EEG study.
abstract: OBJECTIVE
  To investigate the dynamics of communication within the primary somatosensory neuronal network.
  
  
  METHODS
  Multichannel EEG responses evoked by median nerve stimulation were recorded from six healthy participants. We investigated the directional connectivity of the evoked responses by assessing the Partial Directed Coherence (PDC) among five neuronal nodes (brainstem, thalamus and three in the primary sensorimotor cortex), which had been identified by using the Functional Source Separation (FSS) algorithm. We analyzed directional connectivity separately in the low (1-200 Hz, LF) and high (450-750 Hz, HF) frequency ranges.
  
  
  RESULTS
  LF forward connectivity showed peaks at 16, 20, 30 and 50 ms post-stimulus. An estimate of the strength of connectivity was modulated by feedback involving cortical and subcortical nodes. In HF, forward connectivity showed peaks at 20, 30 and 50 ms, with no apparent feedback-related strength changes.
  
  
  CONCLUSIONS
  In this first non-invasive study in humans, we documented directional connectivity across subcortical and cortical somatosensory pathway, discriminating transmission properties within LF and HF ranges.
  
  
  CONCLUSIONS
  The combined use of FSS and PDC in a simple protocol such as median nerve stimulation sheds light on how high and low frequency components of the somatosensory evoked response are functionally interrelated in sustaining somatosensory perception in healthy individuals. Thus, these components may potentially be explored as biomarkers of pathological conditions.
authors.affiliation: LET'S ISTC-CNR, Fatebenefratelli Hospital, Isola Tiberina, 00186 Rome, Italy. camillo.porcaro@istc.cnr.it
authors.forename: Camillo
authors.initials: C
authors.lastname: Porcaro
authors.forename: Gianluca
authors.initials: G
authors.lastname: Coppola
authors.forename: Francesco
authors.initials: F
authors.lastname: Pierelli
authors.forename: Stefano
authors.initials: S
authors.lastname: Seri
authors.forename: Giorgio
authors.initials: G
authors.lastname: Di Lorenzo
authors.forename: Leo
authors.initials: L
authors.lastname: Tomasevic
authors.forename: Carlo
authors.initials: C
authors.lastname: Salustri
authors.forename: Franca
authors.initials: F
authors.lastname: Tecchio
mesh_terms: D000328:Adult; D000465:Algorithms; D001933:Brain Stem / Q000502:physiology; D004558:Electric Stimulation; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology; D025461:Feedback, Physiological; D005260:Female; D006225:Hand / Q000294:innervation* / Q000502:physiology*; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D008959:Models, Neurological; D009044:Motor Cortex / Q000502:physiology*; D009415:Nerve Net / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology*; D011999:Recruitment, Neurophysiological / Q000502:physiology; D012677:Sensation / Q000502:physiology; D013003:Somatosensory Cortex / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D013788:Thalamus / Q000502:physiology