Heritability and association of cortical petalias in rhesus macaques (Macaca mulatta)

Frontal and occipital petalias, the anterior or posterior protrusions of a cerebral lobe on one side or the other, are among the most striking anatomical asymmetries in human brains. Our previous studies of rhesus macaques revealed a relatively high frequency of right frontal petalias, whereas occipital petalias were seen less often and were equally common on right and left sides. In the present study, we test the hypothesis that variation in frontal and occipital lobular morphology is, in part, genetically based, and that frontal and occipital petalias are associated with one another. With a sample of 403 rhesus macaque endocasts, we found that right frontal petalias were more commonly associated with left occipital petalias than would be expected by chance. The concurrence of right frontal and left occipital petalias is the most common variant in human brains. We also found significant but moderate heritability for frontal petalias, while the heritability estimate for occipital petalias was relatively low and not statistically significant. This result suggests a genetic basis for variation in the degree of anatomical cerebral lateralization.