Hand somatosensory subcortical and cortical sources assessed by functional source separation: an EEG study

Camillo Porcaro, Gianluca Coppola, Giorgio Di Lorenzo, Filippo Zappasodi, Alberto Siracusano, Francesco Pierelli, Paolo M. Rossini, Franca Tecchio, Stefano Seri

Research output: Contribution to journalArticlepeer-review


We propose a novel electroencephalographic application of a recently developed cerebral source extraction method (Functional Source Separation, FSS), which starts from extracranial signals and adds a functional constraint to the cost function of a basic independent component analysis model without requiring solutions to be independent. Five ad-hoc functional constraints were used to extract the activity reflecting the temporal sequence of sensory information processing along the somatosensory pathway in response to the separate left and right median nerve galvanic stimulation. Constraints required only the maximization of the responsiveness at specific latencies following sensory stimulation, without taking into account that any frequency or spatial information. After source extraction, the reliability of identified FS was assessed based on the position of single dipoles fitted on its retroprojected signals and on a discrepancy measure. The FS positions were consistent with previously reported data (two early subcortical sources localized in the brain stem and thalamus, the three later sources in cortical areas), leaving negligible residual activity at the corresponding latencies. The high-frequency component of the oscillatory activity (HFO) of the extracted component was analyzed. The integrity of the low amplitude HFOs was preserved for each FS. On the basis of our data, we suggest that FSS can be an effective tool to investigate the HFO behavior of the different neuronal pools, recruited at successive times after median nerve galvanic stimulation. As FSs are reconstructed along the entire experimental session, directional and dynamic HFO synchronization phenomena can be studied.
Original languageEnglish
Pages (from-to)660-674
Number of pages15
JournalHuman Brain Mapping
Issue number2
Early online date11 Feb 2008
Publication statusPublished - Feb 2009


  • adult
  • afferent pathways
  • brain
  • brain Mapping
  • brain stem
  • electric stimulation
  • electroencephalography
  • somatosensory evoked potentials
  • female
  • finite element analysis
  • hand
  • humans
  • male
  • neural conduction
  • neuropsychological tests
  • physical stimulation
  • reaction time
  • somatosensory cortex
  • thalamus
  • touch
  • blind source separation
  • functional constraint
  • somatosensory evoked potential
  • high frequency oscillations
  • 600 Hz


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