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Spinal cord: That's why we become left-handed or right-handed


Right-handed or left-handed? The cause is obviously not in the brain
It has long been assumed that it is determined in the brain whether a person is left-handed or right-handed. But now there is evidence that the cause of handedness is somewhere else - in the spinal cord.

Left-handed people have long been forced to write with their right hand
Left-handedness is nowadays accepted - but not in all regions of the world - as a natural disposition. For a long time it was different. Here in Germany too, left-handed people were forced to write with their right hand until the 1970s. Such "retraining" can lead to serious problems. These include, among other things, a lack of ability to concentrate, memory and speech disorders. It is believed that it is determined in the brain whether someone is left-handed or right-handed. But now there are new insights.

Handedness is not established in the brain
It is not the brain that determines whether people become right-handed or left-handed, but the spinal cord. This is the conclusion reached by biopsychologists from the Ruhr University Bochum (RUB).

As the university reports in a communication, the Bochum scientists, together with colleagues from the Netherlands and South Africa, have demonstrated that gene activity in the spinal cord is asymmetrical even in the womb. A left or right hand preference may be due to this asymmetry.

It was previously thought that differences in the gene activity of the right and left brain could be responsible for a person's handedness.

A preference for movements of the left or right hand develops in the womb from the eighth week of pregnancy, as shown by ultrasound examinations in the 1980s.

From the 13th week of pregnancy, unborn children prefer to suck on either the right or left thumb.

Reason for the right-left preference rather in the spinal cord
As the message goes on, arm or hand movements are initiated via the motor cortex in the brain. This sends a corresponding signal to the spinal cord, which converts the command into a movement.

However, the motor cerebral cortex is not connected to the spinal cord from the start. Even before the connection is established, preliminary stages of handedness are visible.

The researchers therefore assumed that the cause of the right-left preference should be in the spinal cord rather than in the brain. That was also suggested by their results.

Differences already in the eighth week of pregnancy
The researchers led by private lecturer Dr. Sebastian Ocklenburg, Judith Schmitz and Prof. Dr. H. c. Onur Güntürkun found clear right-left differences in the gene expression in the spinal cord in the eighth week of pregnancy - in the spinal cord segments that control the movements of the arms and legs.

From other studies it is known that unborn children are already making asymmetrical hand movements at this point.

"The results fundamentally change our understanding of the origin of hemispherical asymmetries," the authors conclude. (ad)

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