Cerebral Cortex Advance Access originally published online on April 13, 2006
Cerebral Cortex 2007 17(3):610-620; doi:10.1093/cercor/bhk007
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Human SII and Posterior Insula Differently Encode Thermal Laser Stimuli
1 Institut National de la Santé et de la recherche médicale 342, Bron F-69677, France, 2 Univ Lyon1, Lyon F-69000, France, 3 CHU Lyon, Hôpital Neurologique, Service de Neurologie Fonctionnelle et d'Epileptologie, Bron F-69677, France
Address correspondence to Maud Frot, INSERM EMI 342, Hôpital Neurologique, 59 Boulevard Pinel, 69677 Bron, Cedex, France. Email: maud.frot{at}univ-lyon1.fr.
The SII area and the posterior insular region are both activated by thermal stimuli in functional imaging studies. However, controversy remains as to a possible differential encoding of thermal intensity by each of these 2 contiguous areas. Using CO2 laser stimulations, we analyzed the modifications induced by increasing thermal energy on evoked potentials recorded with electrodes implanted within SII and posterior insula in patients referred for presurgical evaluation of epilepsy. Although increasing stimulus intensities enhanced both SII and insular responses, the "dynamics" of their respective amplitude changes were different. SII responses were able to encode gradually the intensity of stimuli from sensory threshold up to a level next to pain threshold but tended to show a ceiling effect for higher painful intensities. In contrast, the posterior insular cortex failed to detect nonnoxious laser pulses but reliably encoded stimulus intensity variations at painful levels, without showing saturation effects for intensities above pain threshold. According to these results, one can assume that insular cortex could be more involved in the triggering of affective recognition of, and motor reaction to, noxious stimuli, whereas SII would be more dedicated to finer-grain discrimination of stimulus intensity, from nonpainful to painful levels.
Key Words: CO2 laser • evoked potentials • intracerebral recordings • posterior insular cortex • SII area • thermal and painful stimuli
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