In human neuroanatomy, brain asymmetry can refer to at least two quite distinct findings:
- Neuroanatomical differences between the left and right sides of the brain
- Lateralized functional differences: Lateralization of brain function
Neuroanatomical differences themselves exist on different scales, from neuronal densities, to the size of regions such as the planum temporale, to—at the largest scale—the torsion or "wind" in the human brain, reflected shape of the skull, which reflects a backward (posterior) protrusion of the left occipital bone and a forward (anterior) protrusion of the right frontal bone. In addition to gross size differences, both neurochemical and structural differences have been found between the hemispheres. Asymmetries appear in the spacing of cortical columns, as well as dendritic structure and complexity. Larger cell sizes are also found in layer III of Broca's area.
The human brain has an overall leftward posterior and rightward anterior asymmetry (or brain torque). There are particularly large asymmetries in the frontal, temporal and occipital lobes, which increases in asymmetry in the antero-posterior direction beginning at the central region. Leftward asymmetry can be seen in the Heschl gyrus, parietal operculum, Silvian fissure, left cingulate gyrus, temporo-parietal region and planum temporale. Rightward asymmetry can be seen in the right central sulcus (potentially suggesting increased connectivity between motor and somatosensory cortices in the left side of the brain), lateral ventricle, entorhinal cortex, amygdala and temporo-parieto-occipital area. Sex-dependent brain asymmetries are also common. For example, human male brains are more asymmetrically lateralized than that of females.
|In cognitive abilities||Geschwind–Galaburda hypothesis|
|In eyes||Ocular dominance|
|Handedness in boxing||Southpaw stance||Orthodox stance|
|Handedness in people|
|Handedness related to|
|Handedness measurement||Edinburgh Handedness Inventory|
|In major viscera||Situs solitus||Situs ambiguus||Situs inversus|
[Game of two halves leads to brain asymmetry http://www.wellcome.ac.uk/News/Media-office/Press-releases/2009/WTX052905.htm]
- Arthur W. Toga & Paul M. Thompson (January 2003). "Mapping Brain Asymmetry". Nature Reviews Neuroscience 4 (1): 37–48. doi:10.1038/nrn1009. PMID 12511860.
- Marko Wilke and Vincent J. Schmithorst (2006). "A combined bootstrap/histogram analysis approach for computing a lateralization index from neuroimaging data". NeuroImage 33 (2): 522–530. doi:10.1016/j.neuroimage.2006.07.010. PMID 16938470.