Early secondary somatosensory area (SII) SEPs. Data from intracerebral recordings in humans.
OBJECTIVE
To record somatosensory evoked potentials (SEPs) to median nerve stimulation by chronically implanted electrodes in the parieto-rolandic opercular area of 9 epileptic patients, in order to evaluate whether somatosensory evoked responses could be generated in the second somatosensory area (SII) earlier than 40 ms after stimulus.


METHODS
Nine patients (4 males, 5 females) with drug-resistant partial epileptic seizures were investigated using stereotactically implanted electrodes in the parietal cortex, posterior to vertical anterior commissure plane and in the frontal opercular region rostral to vertical anterior commissure (VAC).


RESULTS
The main finding of this study is the recording of an early somatosensory evoked potential, (N30op), by chronically implanted electrodes in the SII area of 8 epileptic patients. In 3 patients where SEPs were performed after ipsilateral median nerve (MN) stimulation, a N30op was recorded 5.8+/-2 ms later than contralateral one.


CONCLUSIONS
This is the first report of early SEPs recorded by electrodes implanted in SII area. The N30op potential, even if less consistent than later potentials, confirmed the important role of the SII area in the early processing of somatosensory inputs.
Barba
Carmen
C
Department of Neurology, Catholic University, Largo A. Gemelli 8, 00168 Rome, Italy. carmen.barba@tiscali.it
Frot
M
M
Mauguière
F
F
D000293:Adolescent; D000328:Adult; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D004569:Electroencephalography; D004827:Epilepsy / Q000503:physiopathology; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D010296:Parietal Lobe / Q000502:physiology; D013003:Somatosensory Cortex / Q000502:physiology*; D013238:Stereotaxic Techniques