A Study of the Somatosensory Evoked Potential in Man Using Brain Mapping Techniques

Abstract

Despite studies on the scalp distribution of upper limb SEP components in normal man(Goff et al 1977) and descriptions of the effect on SEP components of discrete cortical lesions (Mauguiére et al 1983), there have been few descriptions of the clinical application of an SEP control population database using ‘brain mapping’ systems. The purposes of this study were to analyze the morphology and topography of the first 56ms of scalp recorded SEP activity from a broad age range of normal control volunteers and to collate a normative database to investigate its effectiveness in the detection of pathology. The control database was used to study patients with discrete cortical lesions to discover whether topographical techniques contributed to knowledge on the origin of the scalp recorded SEP components. Finally to discover whether the use of an SEP topographical mapping database and statistical mapping methods was useful in the detection of abnormalities associated with such lesions. Data from this thesis showed that the perirolandic P22 and N31 SEP components were important measures to examine in cases of lesions affecting the primary somatosensory cortex. The differential affect of such lesions provided important evidence that there are discrete and separate generators for these components. Interpretation of standard deviation maps created by the univariate Z transform software of the Brain Atlas III™ system were of limited value in the detection of SEP abnormalities associated with cortical lesions. A new sagittal polar projection system of local electrode placement was employed to investigate the SEP in a control group. This system was both easy to employ and points could easily and effectively be communicated. A final study investigating the lateralisation of the SEP in schizophrenia could not confirm previous reports of this measure being of value in the diagnosis and classification of this condition.