RELATIVE VALUE OF THE INION AND MID-PARIETAL LOCATIONS AS ADDITIONAL RECORDING SITES IN PATTERN-REVERSAL VISUAL-EVOKED POTENTIALS

Although the P100 response of pattern reversal visual evoked potential s (PRVEPs) is most commonly recorded from the midline occipital site ( MO), the response at this location can occasionally be absent or poorl y defined due to anatomical variability of the visual cortex. In these cases, the American Electroencephalographic Society Evoked Potential Guidelines recommends recording from the mid-parietal (MP) and Inion e lectrode sites. In this study, we compared the amplitude of the P100 c omponent recorded simultaneously from MO, MP and the Inion. PRVEPs obt ained following stimulation with 30' check sizes from 155 consecutive patients (310 eyes) over a 2 year period were analyzed. At each of the 3 recording sites, the peak amplitude of P100 was calculated as N75-P 100, P100-N145, and the sum of N75-P100 and P100-N145. There was a sta tistically significant difference between the electrode sites for all 3 methods of amplitude measurement (one-way ANOVA; P < 0.0001). For ea ch method of measurement, there was no significant difference between P100 amplitude at MO or the Inion, but a significantly reduced amplitu de at MP compared to both the MO and Inion electrode sites (post hoc S cheffe, P < 0.05). The P100 amplitude was highest at the Inion in 18% of responses, including cases where the amplitude at that site was at least twice that at MO. In no case was the amplitude highest at MP. Ou r results indicate that the Inion is a better recording site compared to MP when acquiring PRVEPs, is often complementary to MO, and should be the first additional site to be used when extra channels are availa ble. (C) 1997 Elsevier Science Ireland Ltd.