Left Occipital-Right Frontal Petalia Torque Asymmetry

Petalias are a type of cerebral asymmetry, with greater protrusion of one hemisphere beyond the opposite hemisphere. The most typical configuration in modern humans is for the combination of a right frontal lobe petalia and a left occipital lobe petalia.

This same pattern of petalias are found in modern humans, fossil hominids, and great ape species (see Balzeau et al, 2012 for a review).  Great apes show less variability and less exaggeration in their petalia patterns than modern humans (Balzeau et al, 2012).  Macaque monkeys tend to show a rightward frontal petalia, but not a left-occipital petalia (Falk et al, 1990).

Petalia patterns have been thought to relate to handedness; Galaburda et al (1978) found that right-frontal and left-occipital petalias were found to correlate with right-handedness in modern humans, and the opposite pattern with left-handedness.  However, recent measurements by Balzeau et al (2012) show that variations in the petalias do not relate, putting into question their causal link.  In fact, we have causal links between a gross asymmetry and a functional asymmetry in any domain.  These facts, in addition to the presence of petalias in other primates, calls into question the relationship between petalias and any asymmetric brain functions.