INTERSUBJECT VARIABILITY IN FUNCTIONAL NEUROANATOMY OF SILENT VERB GENERATION - ASSESSMENT BY A NEW ACTIVATION DETECTION ALGORITHM-BASED ONAMPLITUDE AND SIZE INFORMATION

We present an experimental evaluation of a new algorithm for the detec tion of activated areas in brain functional maps. The new algorithm, n amed HMSD, is based on a hierarchical multiscale description of the di fference image in terms of connected objects, Size and magnitude of ea ch object are simultaneously tested with respect to a bidimensional fr equency distribution derived using Monte-Carlo simulations under the n ull hypothesis. In the present work. HMSD was applied to the analysis of a silent verb generation PET activation protocol conducted in six r ight-handed subjects. Applied to single-subject data. HMSD reveals act ivation located in the left inferior frontal gyrus in three subjects ( two in the pars opercularis, one in the pars triangularis), and in the pars opercularis of the right inferior frontal gyrus in one case, the latter being combined to a crossed cerebellar activation, Overall, si ngle case results were consistent with the analyses of stereotacticall y averaged data. Despite a 2D implentation. HMSD detection performance s of averaged data were better than that obtained with the 2D version of statistical parametric mapping (SPM) and comparable to that of the 3D version of SPM. (C) 1995 Academic Press, Inc.