Left Occipital-Right Frontal Petalia Torque Asymmetry

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Petalias are a type of cerebral asymmetry, with greater protrusion of the surface of one hemisphere beyond that of 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.

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