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Mapping Adolescent Brain Change 61et al., 1994) and then flattened to a 2-D planar format (Thompson & Toga, 1997;Thompson & Toga, 2002). A complex deformation, or warping transform, is thenapplied that aligns the sulcal anatomy of each subject with an average sulcal patternderived for the group (see figure 3-2). To improve sulcal alignment acrosssubjects, all sulci that occur consistently can be manually defined on the surfacerendering (see figure 3-3), and used to constrain this transformation. Corticalmeasures, such as gray matter thickness or local brain size, can then be comparedacross subjects and groups to assess age, gender, or group effects. More detailson these methods can be found in other reports (Thompson, Hayashi, et al., 2004).Mapping Sulcal Asymmetries Using CPMLeft-right asymmetries in sulcal patterns are particularly interesting in theperisylvian cortices given the functional lateralization of language in this region(reviewed in Geschwind & Galaburda, 1985). Postmortem studies have shownthat in adults, the Sylvian fissure is longer in the left hemisphere than the right(Galaburda et al., 1978; Ide et al., 1996), and in vivo vascular imaging studieshave shown that the Sylvian fissure angles up more dramatically at its posteriorend in the right hemisphere than the left (LeMay & Culebras, 1972). Left greaterthan right hemisphere perisylvian asymmetries (planum temporale length) havealso been observed in postmortem studies of infants (Witelson & Pallie, 1973),indicating that these asymmetry patterns may be independent of maturationalchange and the acquisition of language abilities throughout infancy and childhood.Until our recent in vivo imaging studies, little was known about the emergence ofcortical surface gyral and sulcal asymmetries in normal adolescent development.In a recent study, we mapped sulcal pattern asymmetry in groups of normallydeveloping children (7 to 11 years), adolescents (12 to 16 years), and young adults(23 to 30 years) using the surface-based cortical pattern matching image analyticmethods described above. Asymmetries in perisylvian cortices continued to developbetween childhood and young adulthood (Sowell et al., 2002b). Althoughthe normal left longer than right Sylvian fissure asymmetry was present in thechildren, adolescents, and adults, it was much more pronounced in adulthood, onaverage twice the magnitude of the asymmetry observed in children. The asymmetryin the slope of the Sylvian fissure also changed with age such that the normalpattern of right more sloped than left occurred without exception in the youngadults studied and significantly less frequently in the children. These findingswere consistent with the earlier postmortem literature, and we observed similarasymmetry patterns in an independent group of children and adolescents (Blantonet al., 2001). The functional significance of these changes in asymmetry is currentlynot well understood, and their relevance to adolescence is even less clear.Maturational cellular events such as continued myelination (Yakovlev &Lecours, 1967) and perhaps even new neurons (Gould et al., 1999) in perisylvianregions could contribute to the dynamic changes in sulcal asymmetry observed