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March 2004 Archives

March 1, 2004

1st March 2004

Laterality and Left Handedness - By Adam Mark

Pop Quiz: What do Ronald Reagan, George Bush and Bill Clinton, have in common? Apart from having the same superannuation policies, all three ex-presidents are left handed. In fact they join the 13% of the population that prefers to use their left hand, or foot for a variety of tasks, including writing, reaching, throwing, pointing, catching, swinging a golf club, standing on a surfboard or kicking a ball.

I know some of you out there are thinking, but my brother's girlfriend's aunt writes right-handed, but plays tennis left handed. Are there any definitive tests to determine handedness? Well, here's a couple of ways to test if you are right handed or non-righthanded. Test 1: Drop a pen on the ground. Pick it up. The hand you pick the pen up with is usually your dominant hand. Test 2: Sitting comfortably, fold your hands together. Make note which thumb is on top. Lefties will have the right thumb on top. Test 3: There is a test that is believed to determine hand preference and hemisphere dominance, called the Torque Test. One draws one's name with one hand, and then circles it. Then one draws the name with the other hand, and circles it. The hand that produced the best handwriting is the hand of preference, and the if the circles were drawn clockwise the right brain is dominant, and counterclockwise circles indicate a left-brain dominance. One circle clockwise and the other counter-clockwise show mixed dominance. Test 4: For the more ambitious, to test for cerebral dominance, which is also related to handedness, get a friend to conduct the Wada test on you. This involves getting Sodium Amytal, an anesthetic injected into the right or left carotid artery. If the right carotid is used the effect is essentially putting the right half of the brain to sleep, likewise the left side when the left carotid is used. The patient is then asked to start counting backwards from 100. If the patient stops talking when the anaesthetic is injected into the left carotid artery, then the left hemisphere is responsible for speech and the dominant hemisphere. 99% of Right handed people are left hemisphere dominant, but only 40% of Left Handed people are right hemisphere dominant. The reason for this occurrence is not fully understood., Another interesting statistic is that there are more Left handed Males than Females. In fact, Males are about one and one half times more likely to be left-handed than females. Such a fact suggests that there may be a hormonal role in the determinance of handedness. Recent studies that have focused on the amount of Testosterone present in the fetus and amniotic fluid during pregnancy have lead to the speculation that an excessive level of testosterone in the fetus slows the development of the left side of the brain, which allows the right side of the brain to achieve and maintain dominance. Due to the fact that a pregnant woman only produces a small amount of testosterone, the actual amount of the hormone, which finds its way into the amniotic fluid during pregnancy, is minute. A male fetus produces some testosterone in the uterus during development while a female fetus will produce no testosterone. Therefore, the chances of testosterone reaching excessive levels are much higher in a male fetus than in a female fetus simply because the normal levels of testosterone for a male fetus are higher in the first place. These results were taken to the next logical step by Canadian researchers Martin Lalu-miere, Ray Blanchard & Kenneth Zucker of the University of Toronto who examined sexual orientation and handedness in homosexual and heterosexual men and women. Their study, published in the July 2000 edition of the Psychological Bulletin, compared the rates of non-right-handedness (that is those who are left handed and ambidextrous) in 6.987 homosexual (6,182 men and 805 women) and 16,423 heterosexual (14,808 men and 1,615 women) men & women. It was found that Homosexual participants had 39% greater odds of being non-right-handed. The corresponding values for homosexual men were 34% and 91%, respectively. Though the results supported the notion that sexual orientation in some men and women has an early neurodevelopment basis, but the fact that someone is left handed doesn't necessarily mean that they will be homosexual. The authors suggest that there may be 3 possibilities: the localization of function within the brain due to prenatal exposure to sex hormones, maternal immunological reactions to the fetus, and developmental instability. The developmental instability hypothesis, which may be due to prenatal damage to the brain, an insufficient supply of oxygen to the brain, and a difficult birth, is supported by the fact that almost 30% of mentally retarded children are left-handed - which is three times the normal statistic for left-handedness. Twins are notorious for having difficult births, and have a high rate of left-handedness too...about 20%, which is twice the normal rate. It is also thought that the tendency to have difficult births is genetic, which would back up the statistics for left-handedness to run in the family. But apart from that it is a well documented that a large proportion of geniuses in the academic, arts, sporting and political fields are southpaws. So in closing without the left-handed people of the world, the right-handed people wouldn't know what is going on.

March 3, 2004

Ian Woolf

Ian Woolf lives in Sydney, has a degree in Applied Physics, worked as a solar astronomer, software engineer, systems programmer, webmaster, Cisco CCNA tutor, Computational Theory lecturer, and subject coordinator; while changing his career to professional writing and broadcasting. Read more at Here's Why

March 15, 2004

15th March 2004

March 22, 2004

22 March 2004

March 29, 2004

29 March 2004

About March 2004

This page contains all entries posted to Diffusion Science radio in March 2004. They are listed from oldest to newest.

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