Comparison of Perirolandic Sensorimotor Function Using Somatosensory Evoked Potentials and Brain Stimulation in Patients with Epilepsy

Seo, Dae Won; Hong, Seung Bong

Abstract

BACKGROUND: The detection of the phase reversal of somatosensory evoked potentials (SEP) has been well known to be a safe and reproducible method for defining the sensorimotor cortex. Brain stimulation (BS) has also been used to identify functional loci. The two tests, however have not to be compared in the cortical localization of the sensorimotor cortex yet.
METHODS
We recorded the cortical potentials to median nerve stimulation from subdural grids which were in the frontoparietal areas of 12 epilepsy patients. After looking for phase reversals, we compared positive motor and sensory responses by brain stimulation from each electrode. In addition, the maximal amplitude areas of precentral positivity (max-P20) and postcentral negativity (max-N20) were analyzed, which were then compared with BS results.
RESULTS
All patients showed phase reversals (average:4.7+1.61) on cortical SEP to median nerve stimulation. The electrodes before the phase reversal line had positive motor responses in 75% among electrodes with positive motor responses. The electrodes after the phase reversal line had positive sensory responses in 88.9% among electrodes with positive sensory responses. The maximal amplitude areas were recorded within a 2cm distance to the central sulcus. Max-P20's were located on the areas where BS showed a finger in 5 patients, hand in 3, forearm in 2, and tongue motor response in 2. Max-N20's were recorded on the areas where BS revealed a hand in 4 patients, forearm in 1, and undetected sensory responses in 7.
CONCLUSIONS
These results suggest that SEP is different from BS in the functional localization of the perirolandic area. Thus, combined functional evaluation of the periolandic area by SEP as well as by BS is helpful in assessing sensorimotor functions.