title: Trigeminal somatosensory evoked magnetic fields to tactile stimulation.
abstract: OBJECTIVE
  To characterise the activation of the contra- and ipsilateral primary somatosensory cortex (SI) after tactile stimulation of the face.
  
  
  METHODS
  Trigeminal somatosensory evoked magnetic fields (TSEFs) were recorded after tactile stimulation of the lower lip, cheek, chin and forehead in 11 healthy subjects. The responses were determined visually from the waveforms and modelled with equivalent current dipoles (ECDs).
  
  
  RESULTS
  Contralateral SI responses were evoked in all subjects after lip stimulation, and in 91% and 64% after right and left cheek, 73% and 82% after chin and 64% and 27% after forehead stimulation. The responses usually showed an early double-peak wave pattern, the underlying sources localising to the SI. In addition, altogether 37 ipsilateral SI responses were evoked in eight subjects. Fourteen of these responses were amenable to ECD modelling and localised to ipsilateral SI.
  
  
  CONCLUSIONS
  Tactile stimulation of the lip area reliably activates the contralateral SI in normal subjects, but the success rate for other trigeminal areas is lower. Ipsilateral responses can be present after stimulation of any of the trigeminal branches in normal subjects.
  
  
  CONCLUSIONS
  Recording of TSEFs after tactile stimulation of particularly the lip area provides a non-invasive technique to study the function of the trigeminal nerve.
authors.affiliation: BioMag Laboratory, Helsinki University Central Hospital, P.O. Box 340, FIN-00029 HUS, Finland.
authors.forename: P
authors.initials: P
authors.lastname: Nevalainen
authors.forename: R
authors.initials: R
authors.lastname: Ramstad
authors.forename: E
authors.initials: E
authors.lastname: Isotalo
authors.forename: M-L
authors.initials: ML
authors.lastname: Haapanen
authors.forename: L
authors.initials: L
authors.lastname: Lauronen
mesh_terms: D000328:Adult; D001931:Brain Mapping; D004574:Electromagnetic Fields; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005145:Face / Q000294:innervation; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged; D011930:Reaction Time / Q000502:physiology; D013003:Somatosensory Cortex / Q000502:physiology*; D014110:Touch / Q000502:physiology*; D014276:Trigeminal Nerve / Q000502:physiology*