Leftward Asymmetry of Broca's Area

Broca’s area in humans has evolved a distinctive degree of anatomical asymmetry. Humans have been shown to display left hemisphere dominance of neuropil space and pyramidal neuron dendritic branching in Broca’s region (reviewed in Schenker et al., 2007), and the cytoarchitectonic areas that comprise Broca’s region (BA44 and BA45) have a greater volume in the left hemisphere as compared with the right in humans (Amunts et al., 1999). Further t this point, the size of BA44 and BA45  in 5-6 times greater than in chimpanzees (Schenker et al., 2010).  Additionally, some MRI studies have shown asymmetry of inferior frontal gyrus morphology in humans (Falzi et al., 1982; Tomaiuolo et al., 1999; Foundas et al., 2001), though others have not (Keller et al., 2009). Studies of chimpanzees and other great apes have shown left hemisphere dominance in several measures of inferior frontal gyrus morphology (Cantalupo and Hopkins, 2001 but see Keller et al., 2009), although the underlying BA44 and BA45 of chimpanzees do not display significant population level asymmetry (Schenker et al., 2010).