BOOTSTRAP ASSESSMENT OF THE RELIABILITY OF MAXIMA IN SURFACE MAPS OF BRAIN ACTIVITY OF INDIVIDUAL SUBJECTS DERIVED WITH ELECTROPHYSIOLOGICAL AND OPTICAL METHODS

Surface maps of brain activity can be obtained with electrophysiologic al and optical recordings. However, there are no established methods f or determining the reliability of maps of brain activity across subjec t groups or across tasks within the same subject. In this paper, we us e bootstrapping to establish the reliability of the locations of maxim a in maps of surface brain activity of individual subjects obtained wi th ERP and optical (EROS) recordings and report sample analyses for tw o data sets. Bootstrapping is a nonparametric method for estimating st atistical accuracy from the data in a single sample. The distribution of the statistic of interest is estimated by constructing ''bootstrap samples'' from a pool of all available cases (with replacement). Many ''bootstrap replications'' are obtained by calculating the statistic o f interest for each sample. In the case of brain activity, many (e.g., 10,000) amplitude distributions can be derived from the data of an in dividual subject. Frequency counts are then computed for each recordin g location to establish how many times that location corresponds to a maximum. The value obtained in this fashion represents an estimate of the reliability of the observation.