The presence of asymmetry in the human cerebral hemispheres is detectable at both the macroscopic and microscopic levels. An association between these asymmetries is inferred but not yet supported by statistical analysis.
Asymmetries seen in comparative studies provide strong evidence for phylogenetic origins of brain lateralization.
Two components of macroscopic asymmetry of Cerebral Hemispheres are known.
One is “PETALIA” and another is “VOLUME TORQUE”.
“PETALIA” term describes asymmetrical protrusion of one part of cerebral hemisphere beyond the other. CT and MRI studies show that these petalias are more prominent in right handers. Among the most prominent observations of brain asymmetry are the right frontal and left occipital 'petalias', the right hemisphere protrudes anteriorly beyond the left, and the left hemisphere extends posteriorly beyond the right.
“VOLUME TORQUE” is a differential distribution of tissue of a cerebral hemisphere compared to other. The right frontal region is often wider than the left, and the left occipital region is often wider than the right, reflect lateralized volume differences in frontal and occipital regions and is associated with language function in humans, not found in other apes.
“Yakovlevian anticlockwise torque” encompasses includes petalia plus the frequent extension of the left occipital lobe across the midline over the right occipital lobe, bending the interhemispheric fissure towards the right.
Arthur W. Toga and Paul M. Thompson, Laboratory of Neuro Imaging , Department of Neurology, UCLA School of Medicine, Los Angeles, CA, USA MAPPING BRAIN ASYMMETRY
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