Right-left asymmetry in anterior speech region.

The extent of the anterior speech region (defined as pars opercularis and pars triangularis of the third frontal convolution) and of the planum temporale was measured in 12 brains belonging to strictly right-handed persons. When the portion of the anterior speech region visible on the hemispheric surface was measured, no interhemispheric difference was found. By contrast, when both the extrasulcal and intrasulcal portions of cortex were considered, the anterior speech region in the left hemisphere was found to be significantly larger than the homologous areas in the right hemisphere. The planum temporale was significantly larger on the left than on the right, but there was no necessary correspondence between the presence of a larger right planum and a larger right anterior speech region.