The end point of the sylvian fissure is higher on the right than the left in cat brain as in human brain

Sex differences in asymmetry of the planum parietale in chimpanzees (Pan troglodytes)

Magnetic resonance images were collected in 76 chimpanzees and the sylvian fissure was examined for the presence of a posterior bifurcation. A bilateral bifurcation of the sylvian fissure into an ascending and descending ramus was identified in 58 of the subjects. The posterior ascending ramus was measured in both hemispheres in order to evaluate the presence, magnitude, and direction of a planum parietale asymmetry. Statistical analysis revealed a main effect for sex. Specifically, females showed a significant rightward bias, whereas males did not. Moreover, an examination of posterior bifurcation patterns of the sylvian fissure revealed differences between the left and right hemispheres. In humans, subject handedness and sex have been found to have an effect on planum parietale asymmetry. To determine if this was also the case in our chimpanzee subjects, we evaluated whether or not planum parietale asymmetry was related to subject handedness. Although subject handedness was not directly related to planum parietale asymmetry quotients, whether or not the sylvian fissure bifurcated bilaterally at its posterior end was influenced by the handedness of the subjects. These results support the view that asymmetries in the perisylvian language areas were present in the common ancestor of humans and chimpanzees.

Asymmetries in cerebral width in nonhuman primate brains as revealed by magnetic resonance imaging (MRI)

A comparative study of asymmetries in cerebral width was conducted in a sample of great apes, Old World and New World monkeys. The brains of all subjects were scanned using magnetic resonance imaging (MRI) and the first axial slice above the third ventricle was identified. Measures of cerebral width were taken at distances of 10% and 30% of the length from the occipital and frontal poles. Cerebral widths were measured from the midline to the lateral surface of the brain for each area. The great apes exhibited a right-frontal and left-occipital directional asymmetry in cerebral width. In contrast, no significant mean directional asymmetries were found in either the Old or New World monkeys. The results in the great apes are consistent with previous reports of petalia asymmetries and suggest that the use of MRI is a valid approach to the assessment of neuroanatomical asymmetries in primates.

Facial asymmetry in right- and left-handed men and women

A posteroanterior cephalometric radiographic study was performed on the right- and left-handed men and women with normal occlusion. A posteroanterior cephalometric radiography was conducted in these subjects. Method of triangulation was used to measure various face areas. The surface areas of these triangles were compared with their equivalents on the contralateral side. Sex and its interactions with handedness and side were significant factors influencing facial areas. Areas on the left were found to be significantly larger than those on the right in right-handers. Left-handers were inconsistent in facial asymmetry, but they tended to have larger facial areas on the right than the left. Sex was especially significant for left-handers. It was suggested that an asymmetric development in some brain regions may be responsible for the development of asymmetric facial regions.