It has been assumed for a long time that it is determined in the brain whether a person is left or right handed. But now there are indications that the cause of the handiness lies elsewhere - in the spinal cord.
Lefthanders have long been forced to write with the right hand
Left handedness is nowadays accepted - but not in all world regions - as a natural predisposition. For a long time it was different. Again, left-handers were forced to write with their right hands until the 1970s. Such "retraining" can lead to serious problems. Among other things, these include the lack of concentration, 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.
Handiness is not determined in the brain
Whether humans are right-handed or left-handed, does not determine the brain but the spinal cord. Biopsychologists from the Ruhr-University Bochum( RUB) come to this conclusion.
As reported by the university in a communication, the Bochum scientists, together with colleagues from the Netherlands and South Africa, have shown that gene activity in the spinal cord is already asymmetric in the mother's body. A preference for left or right hand could be due to this asymmetry.
Up to now it was assumed that differences in the gene activity of the right and left cerebral hemispheres could be responsible for a man's hand.
A preference for movements of the left or right hand is already apparent in the mother's body as from the eighth gestational week, as ultrasound examinations of the 1980s.
From the 13th week of pregnancy unborn children either prefer to suck on the right or the left thumb.
Cause for the right-left preference rather in the spinal cord
As the message further states, arm movements or hand movements are initiated via the motor cortex in the brain. This sends a corresponding signal to the spinal cord, which translates the command into a movement.
However, the motor cerebral cortex is not connected to the spinal cord from the beginning. Even before the connection forms, preliminary stages of the handiness are visible.
The researchers therefore assumed that the cause of the right-left preference should lie in the spinal cord rather than in the brain. This also suggested their results.
differences already in the eighth pregnant women's week
The researchers around Privatdozent Dr. Sebastian Ocklenburg, Judith Schmitz and Prof. Dr. Dr. H.c. Onur Güntürkün found clear right-left differences in gene expression in the spinal cord during the eighth gestational week - precisely in the spinal cord segments, which control movements of the arms and legs.
It is known from other studies that unborn children are already doing asymmetrical movements at this time.
"The results fundamentally change our understanding of the origin of hemispherical asymmetry," the authors conclude.(ad)