Visual pattern comparison, working memory load, and event related potentials

Abstract

This chapter reviews certain studies on somatosensory evoked field (SEF) dipolar source modeling to show how clinical and physiological SEP studies can benefit from this type of approach. Studies on dipolar source modeling of the early lower limb SEPs have offered a significant contribution in identifying the tibial nerve SEP generators. By using the brain electrical source analysis (BESA), two different dipoles contributing to the potential field in the N37–P40 latency range are shown. A tangential dipole oriented perpendicularly to the mesial hemispheric wall generated both the N37 potential and a subcomponent of the P40 potential located in the ipsilateral parietal region, whereas a radial dipole in the crown of the perirolandic cerebral cortex represented the source of the vertex subcomponent of the P40 SEP. In the presurgical assessment of patients with space occupying lesions around the sensorimotor cortex, the localization of the central fissure by brain magnetic resonance imaging (MRI) is made difficult by the displacement induced by the lesion. The chapter underlines the technical limitations that have to be considered in evaluating the results of dipolar analysis.