USING in vivo magnetic resonance morphometry we measured the posterior
wall of the left and right posterior ascending portion of the Sylvian
fissure, an inferior parietal area of the brain that we have termed t
he planum parietale. Among 106 right-handers (53 women and 53 men) and
35 left-handers (18 women and 17 men), handedness and gender exerted
an interactive influence on planum parietale asymmetry; right-handed m
en and left-handed women showed particularly strong rightward asymmetr
y. There was no correlation between asymmetry of the planum parietale
and that of the anatomically adjacent planum temporale, suggesting an
independency of these two structural markers of brain laterality.