Asymmetries of the auditory areas of the cerebrum.

A total of 29 human cadaver brains were examined for asymmetries of the left and right Sylvian fissure, Heschl's gyri, and planum temporale. The mean lengths of these structures were all significantly greater on the left side than on the right. There was considerable morphologic variability in these structures as evidenced by the number of Heschl's gyri that ranged from one to three per hemisphere in different brains, although there was no significant asymmetry in the number of Heschl's gyri in individual brains. Asymmetry of the Sylvian fissure was correlated with the greater length of the planum temporale on the left side. Although it is well known that the planum temporale is larger in the left hemisphere than in the right, little has been reported on Heschl's gyri in this regard. It is possible that asymmetries in higher auditory and language function may be attributable to anatomic asymmetries of not only the planum temporale but also Heschl's gyri.