Genetic Expression may Determine Handedness

There is a nice review in Nature Reviews Neuroscience on the mechanism that causes asymmetry in the brain. One of the theories discussed is that molecules produced in the embryonic brain that induce cell specialization are distributed asymmetrically in the hemispheres, which starts a chain reaction leading to hemispheric specialization. Competing theories have suggested fetal position, or development that occurs postpartum.

Handedness is interesting to neuroeconomists and others because imaging studies frequently exclude left-handed individuals because activation patterns in left-handed individuals are inconsistent even among lefties, and don't correlate well with data obtained from right-handed individuals.

Almost of equal interest in this review is the fact that hemispheric specialization may be influenced by the "Sonic Hedgehog" gene. I'm glad that (a) I have a Sonic Hedgehog gene and (b) such a gene exists in the first place.

Comments

[kevin denny]

For evidence on the genetics of handedness see Francks, C., DeLisi, L. E., Fisher, S. E., Laval, S. H., Rue, J. E., Stein, J. F., Monaco, A. P. (2003). Confirmatory evidence for linkage of relative hand skill to 2p12-q11. (Letter) American Journal of Human Genetics. 72 (2), 499-502
For evidence on handedness & economics see Denny K. & O’Sullivan V.(2007). The economic consequences of being left-handed: some sinister results, Journal of Human Resources, forthcoming. See also a paper by R Moffitt et al forthcoming in Laterality

[Dr. Troy Camplin]

As a leftie myself, I have been interested in the underpinnings of left handedness for a while. I've run across the argument that there is a correlation between testosterone levels during brain development and handedness (in the half that are not caused by brain trauma). If this is the case, it may explain some aspects of handedness and also suggest a direction in such research. For example, left-handedness seems to run in families, though not in a Punet-Square kind of way. It runs in my family, for example -- I have several cousins who are lefties, as are an uncle and my brother. I am also pretty certain that my daughter is a lefties -- though she's only 10 mo. old, so I don't know for certain. But she does seem to prefer using her left hand over her right. I have even witnessed her reach over her body to grab something with her left hand that was more readily reachable by her right hand.

Now, knowing my family, including my father, as well as I do, combined with what I know of what my wife and I did during her pregnancy, it may be interesting to see if there is a correlation between frequency of sex during pregnancy and left handedness. This is assuming that such activity would affect testosterone levels in utero.