Topographic mapping of electrophysiologic measures in patients with homonymous hemianopia We analyzed electroencephalographic (EEG) activity and spatial distribution of the pattern-reversal visual evoked potential (PVEP) in 20 patients with unilateral lesions in the retrochiasmal visual pathways. Focal abnormalities that were consistent with lesion location were present in the topographically analyzed EEG or VEP of 85% of the patients, compared with a 70% detection rate for conventional analysis techniques. Quantitative analysis of spectrally analyzed EEG revealed focal abnormality in 7 patients whose conventional EEG was interpreted as either normal or diffusely slow. However, focal paroxysmal spikes present in the EEG of 1 patient were missed by EEG mapping, and a false localization of quantitative EEG abnormality contralateral to the lesion occurred in 1 patient. Topographic analysis of the PVEP was no more sensitive to retrochiasmatic lesions than conventional analysis of 2 lateral occipital electrodes. We conclude that topographic mapping is a valid technique in the detection of localized cerebral lesions. 