title: Scalp distribution of the earliest cortical somatosensory evoked potential to tibial nerve stimulation: proposal of a new recording montage.
abstract: OBJECTIVE
  To investigate the most reliable method to record the earliest cortical somatosensory evoked potential (SEP) after tibial nerve stimulation. The 'gating' phenomenon was used to dissociate the overlapping cortical SEP components.
  
  
  METHODS
  In 11 subjects we recorded the scalp SEPs at rest, during the voluntary (active gating) and passive (passive gating) foot movement and during the isometric calf muscle contraction (isometric gating).
  
  
  RESULTS
  At the vertex the P40 amplitude was reduced in all the gating conditions. Instead, both the P40 response recorded in the parietal region ipsilateral to the stimulation (indicated as P40par) and the fronto-temporal N37 potential were reduced in amplitude only during the passive foot movement.
  
  
  CONCLUSIONS
  The same behaviour of the N37 and P40par potentials suggests that they can represent the opposite counterparts of the same dipolar generator. Instead, the real P40 amplitude, which is affected in all the gating conditions, is recorded at the vertex and might be generated by a different source. We conclude that the montage obtained by referring a temporal electrode contralateral to the stimulation to an ipsilateral parietal lead can reliably record the earliest cortical component (N37/P40par) after tibial nerve stimulation.
authors.affiliation: Department of Neurology, Università Cattolica del Sacro Cuore, L.go A. Gemelli 8, 00168 Roma, Italy. m.valeriani@tiscalinet.it
authors.forename: M
authors.initials: M
authors.lastname: Valeriani
authors.forename: D
authors.initials: D
authors.lastname: Restuccia
authors.forename: D
authors.initials: D
authors.lastname: Le Pera
authors.forename: C
authors.initials: C
authors.lastname: Barba
authors.forename: P
authors.initials: P
authors.lastname: Tonali
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D004558:Electric Stimulation; D004569:Electroencephalography / Q000379:methods*; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D011930:Reaction Time / Q000502:physiology; D013979:Tibial Nerve / Q000502:physiology*; D013997:Time Factors