A team of researchers from Ruhr-Universität Bochum have traced the cause of asymmetric gene activity that results in preference for left-handedness to right-handedness much before it was previously thought. Much before the development of the brain and motor cortex link with spinal cord, the baby develops preference for left or right handedness, the said.
Epigenetic factors appear to be at the root of it, which lead to enzymes bonding methyl groups to the DNA, which in turn would affect and minimise the reading of genes. As this occurs to a different extent in the left and the right spinal cord, there is a difference to the activity of genes on both sides, they explained.
So far, the popular belief is that preference for moving the left or right hand in the womb from the 18th week of pregnancy, and some new studies said that from the 13th week of pregnancy, unborn children prefer to suck either their right or their left thumb, thus developing this trait.
The hand movements are handiwork of the motor cortex in the brain that sends a corresponding signal to the spinal cord, which in turn translates the command into a motion. But the motor cortex is not connected to the spinal cord from the beginning. In fact, the preference for left or right handedness begins even before the brain-spinal cord connection forms, they said.
Hence, the researchers have assumed that the cause of left preference must have been rooted in the spinal cord rather than in the brain. After studying the gene expression in the spinal cord during the 8th and 12th week of pregnancy, they detected marked right-left differences in the eighth week itself, precisely in those spinal cord segments that control the movements of arms and legs.
The researchers have traced it to epigenetic factors, reflecting environmental influences, which might lead to enzymes bonding methyl groups to the DNA, which in turn would affect and minimise the reading of genes. As this occurs to a different extent in the left and the right spinal cord, there is a difference to the activity of genes on both sides, they said.
“These results fundamentally change our understanding of the cause of hemispheric asymmetries,” said the authors, whose findings will be published in the journal eLife.