Visual evoked response: Isoelectric line and linear regression

The aim of this study was to define as objectively as possible the isoelectric line for visual evoked response (VER). Fifty VER were recorded from 5 normal subjects after stimulation using a reversal checkerboard coloured pattern: French prototype GEPCO. We first established, for each of the SO tracings, the locus of the isoelectric points (t_n,v_0,n), where n varied from 1 to 240. For an associated temporal interval [t₀,t_n], each isoelectric point defined an ordinate horizontal v_0,n ("temporary" isoelectric line) able to bring about the cancellation of the algebraic smn of the surface areas below the VER. Next, for each of the 50 tracings, we defined 20 straight regression lines : the first between the last 41 isoelectric points, the second between the last 51 points and up to the 20 between the 241 points Finally taken into account. Lastly a validity criterion allowed ns to choose from the 20 a straight regression line D*, whose origin ordinate was b*. We then passed a horizontal through the point (0,b*) to obtain our new isoelectric line defining the "resting potential" v₀* = b*.