title: Ipsi- and contralateral EEG reactions to transcranial magnetic stimulation.
abstract: OBJECTIVE
  Transcranial magnetic stimulation (TMS) and high-resolution electroencephalography (EEG) were used to study the spreading of cortical activation in 6 healthy volunteers.
  
  
  METHODS
  Five locations in the left sensorimotor cortex (within 3cm(2)) were stimulated magnetically, while EEG was recorded with 60 scalp electrodes. A frameless stereotactic method was applied to determine the anatomic locus of stimulation and to superimpose the results on magnetic resonance images. Scalp potential and cortical current-density distributions were derived from averaged electroencephalographic (EEG) data.
  
  
  RESULTS
  The maxima of the ipsilateral activation were detected at the gyrus precentralis, gyrus supramarginalis, and lobulus parietalis superior, depending on the subject. Activation over the contralateral cortex was observed in all subjects, appearing at 22plus minus2ms (range 17--28); the maxima were located at the gyrus precentralis, gyrus frontalis superior, and the lobulus parietalis inferior. Contralateral EEG waveforms showed consistent changes when different sites were stimulated: stimulation of the two most medial points evoked the smallest responses fronto-parietally.
  
  
  CONCLUSIONS
  With the combination of TMS, EEG, and magnetic resonance imaging, an adequate spatiotemporal resolution may be achieved for tracing the intra- and interhemispheric spread of activation in the cortex caused by a magnetic pulse.
authors.affiliation: Department of Physics, University of Helsinki, P.O. Box 9, FIN-00014, Helsinki, Finland.
authors.forename: Soile
authors.initials: S
authors.lastname: Komssi
authors.forename: Hannu J
authors.initials: HJ
authors.lastname: Aronen
authors.forename: Juha
authors.initials: J
authors.lastname: Huttunen
authors.forename: Martti
authors.initials: M
authors.lastname: Kesäniemi
authors.forename: Lauri
authors.initials: L
authors.lastname: Soinne
authors.forename: Vadim V
authors.initials: VV
authors.lastname: Nikouline
authors.forename: Marko
authors.initials: M
authors.lastname: Ollikainen
authors.forename: Risto O
authors.initials: RO
authors.lastname: Roine
authors.forename: Jari
authors.initials: J
authors.lastname: Karhu
authors.forename: Sauli
authors.initials: S
authors.lastname: Savolainen
authors.forename: Risto J
authors.initials: RJ
authors.lastname: Ilmoniemi
mesh_terms: D000328:Adult; D000368:Aged; D004558:Electric Stimulation; D004569:Electroencephalography; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D013003:Somatosensory Cortex / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation