INTERSUBJECT VARIABILITY OF FUNCTIONAL AREAS IN THE HUMAN VISUAL-CORTEX

Intersubject variability of striate and extrastriate areas was mapped by conjoined use of positron emission tomography (PET) and magnetic re sonance imaging (MRT). We used two dynamic bowtie-shaped random-dot pa tterns centered symmetrically around the vertical- and horizontal-meri dian, respectively, presented during sequential PET scans in 11 subjec ts. Control condition was simple fixation on a central dot in absence of a surrounding random dot pattern. V1, V2, VP, V3, V3a, V4, V5, and ''wordform'' areas were identified. After spatial normalization to Tal airach atlas space, mean locations and standard deviations about these mean locations for x-, y-, and z-axes were calculated for each area i n both hemispheres and compared for differences. The mean standard dev iation for all axes across all areas tested was found to be small (4.9 mm). No significant differences were found in the mean standard devia tions for the x-, y-, and z-axes in the left hemisphere vs. their coun terparts in the right hemisphere. However, when mean standard deviatio ns in both hemispheres were polled together by axis, the mean standard deviation for the y-axis (5.3 mm) was found to be significantly diffe rent from the mean standard deviation for the x-axis (4.3 mm). Further more, in the left hemisphere, the mean standard deviation for the z-ax is (5.7 mm) was significantly greater than the mean standard deviation for the x-axis (3.9 mm). The values reported in this study for mean l ocation and standard deviation of visual areas can be used to establis h confidence intervals for distinguishing normal variations from patho logy and consequent brain reorganization. Hum. Brain Mapping 6:301-315 , 1998. (C) 1998 Wiley-Liss, Inc.