• Massimiliano Valeriani, Carmen Barba, Domenica Le Pera, Domenico Restuccia, Gabriella Colicchio, Pietro Tonali, Olga Gagliardo, and Rolf Detlef Treede.
• Department of Neurology, Università Cattolica del Sacro Cuore, L.go A. Gemelli 8, 00168 Rome, Italy. m.valeriani@tiscali.it
• Clin Neurophysiol. 2004 Jan 1; 115 (1): 211-6.

ObjectiveTo investigate the possible contribution of the primary somatosensory area (SI) to pain sensation.MethodsDepth recordings of CO2 laser evoked potentials (LEPs) and somatosensory evoked potentials (SEPs) were performed in an epileptic patient with a stereotactically implanted electrode (Talairach coordinates y=-23, z=40) that passed about 10 mm below the hand representation in her left SI area, as assessed by the source of the N20 SEP component.ResultsThe intracerebral electrode was able to record the N20 SEP component after non-painful electrical stimulation of her right median nerve. The N20 potential showed a phase reversal in the bipolar montage (at about 31 mm from the midline), which confirms that the electrode was located near its generator in area 3b. In contrast, no reliable response was recorded from the SI electrode after painful CO2 laser stimulation of the right hand. An N2-P2 response was evoked at the vertex electrode (Cz), thus demonstrating the effectiveness of the delivered CO2 laser stimuli.ConclusionsSince the N20 SEP component originates from the anterior bank of the post-central gyrus (area 3b), our result suggests that this part of SI does not participate in LEP generation. In fact, the previously published LEP sources in the SI area estimated from scalp recordings are about 10-17 mm posterior of the electrode in our patient, suggesting that they are more likely located in area 1, 2 or posterior parietal cortex.

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