title: Distinct fronto-central N60 and supra-sylvian N70 middle-latency components of the median nerve SEPs as assessed by scalp topographic analysis, dipolar source modelling and depth recordings.
abstract: OBJECTIVE
  To investigate the possible contribution of the second somatosensory (SII) area in the generation of the N60 somatosensory evoked potential (SEP).
  
  
  METHODS
  In 7 epileptic patients and in 6 healthy subjects scalp SEPs were recorded by 19 electrodes placed according to the 10-20 system. All epileptic patients but one were also investigated using depth electrodes chronically implanted in the parieto-rolandic opercular cortex. Scalp SEPs underwent brain electrical source analysis.
  
  
  RESULTS
  In both epileptic patients and healthy subjects, scalp recordings showed two middle-latency components clearly distinguishable on the basis of latency and scalp distribution: a fronto-central N60 potential contralateral to stimulation and a later bilateral temporal N70 response. SEP dipolar source modelling showed that a contralateral perisylvian dipole was activated in the scalp N70 latency range whereas separate perirolandic and frontal sources were activated at the scalp N60 latency. Depth electrodes recorded a biphasic N60/P90 response in the parieto-rolandic opercular regions contra- and ipsilateral to stimulation.
  
  
  CONCLUSIONS
  Two different middle-latency SEP components N60 and N70 can be distinguished by topographic analysis and source modelling of scalp recordings, the sources of which are located in the fronto-central cortex contralateral to stimulation and in the supra-sylvian cortex on both sides, respectively. The source location of the scalp N70 in the SII area is strongly supported by its spatio-temporal similarities with SEPs directly recorded in the supra-sylvian opercular cortex.
authors.affiliation: Department of Neurology, Università Cattolica del Sacro Cuore, Rome, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Barba
authors.forename: M
authors.initials: M
authors.lastname: Frot
authors.forename: M
authors.initials: M
authors.lastname: Valeriani
authors.forename: P
authors.initials: P
authors.lastname: Tonali
authors.forename: F
authors.initials: F
authors.lastname: Mauguière
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology; D002540:Cerebral Cortex / Q000502:physiology*; D004567:Electrodes, Implanted; D004569:Electroencephalography; D004594:Electrophysiology; D004827:Epilepsy / Q000175:diagnosis* / Q000503:physiopathology; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008475:Median Nerve / Q000502:physiology*; D008954:Models, Biological; D012016:Reference Values; D012535:Scalp / Q000033:anatomy & histology*; D013238:Stereotaxic Techniques