each successively more distant donut area deviates from its expected trajectory by this technique one can determine whether a lesion is growing in one place or expanding or both the second procedure is to decide on an a priori basis which areas one wishes to follow characteristically the head can be broken into quadrants or further subdivided along known anatomical boundaries by the creation of a template or series of templates the third technique is a retrospective procedure where one follows a subject for a period of time and then performs a retrospective analysis to locate regions which appear to be changing for example if a subject is studied over three or more times preferably 10 or more times then a one way analysis of variants can be performed for each electrode the resulting f statistic can be plotted and regions above a criterion level at the 05 probability point can be defined as 34 templates 34 one then can plot the change of value under the template to determine whether or not the trajectories are showing a monotonic increase or decrease a finding of interest if any regions are found of interest these can then be followed prospectively in short there are three ways to choose templates in the first one defines the region to be followed.