The actual cause of our left- or right-handedness

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Our dominant hand is predetermined before birth, despite popular belief. The cause appears to be elsewhere in the brain.

Do you have left- or right-handedness? A study has shown what determines which side is prominent in our lives. Long believed to be determined by left- or right-handedness, this theory has since been refuted. It has nothing to do with the structure or development of our brain. Our prenatal biology holds the key to the puzzle. According to ultrasound tests conducted in the 1980s, a preference for the movements of the left or right hand is created in the womb as early as the eighth week of pregnancy. Unborn children begin to selectively suck their thumbs—the right or left—around the thirteenth week of life.

Under the direction of biophysicists at Ruhr University in Bochum, Germany, researchers from Germany, the Netherlands, and South Africa have discovered that a specific combination of gene activity in our spine rather than the brain determines which hand is our dominant hand. This discovery asks whether a person’s dominant hand determines which side of their brain is more active.

Researchers saw how unborn children’s spinal cords developed between the eighth and the twelfth weeks of pregnancy, and their findings were published in the journal eLife. Interestingly, this occurs before the motor cortex, the area of the brain responsible for controlling hand movements, attaches itself to the spinal cord. The parts of the spine that transmit signals to our hands, arms, legs, and feet are related. Whether or not we write with our right or left hand depends on this exercise.

The researchers stressed that external influences can still cause this activity, even in a developing embryo. They were unable to pinpoint the exact cause of the action, though. It’s believed that factors in the infant’s surroundings could alter how enzymes function. Genes react to an enzyme’s activity. This results in a specific combination of gene activity in the spine that determines the baby’s future hand preference—right or left.

Information on the relationship between a fetus’s thumb-sucking behaviour and left-handedness was also revealed. Ninety percent of the 274 fetuses surveyed preferred to suck their right thumb after 13 weeks, whereas just ten percent sucked their left, according to the report on thumb sucking. In a reexamination of the infant population, it was discovered that sixty of the fifteen babies who selected the right thumb were right-handed, and ten of the babies who chose the left thumb were left-handed.

  • hector pascua with reports from heute.at/picture:
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