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Coordination of motor functions on the basis of visual information – in pigeons, this task is performed by the left hemisphere. Credit: RUB, Marquard
The left and right hemispheres specialize in different tasks. However, we have not yet understood how one hemisphere takes over the other when it comes to controlling specific functions. Biopsychologists from Ruhr-Universität Bochum describe their latest findings in the journal Cell reports, published online 30 October 2018. Dr. Qian Xiao and Professor Onur Güntürkün have demonstrated in pigeons that dominance is caused by slight differences in temporal patterns of activity in both hemispheres.
New research approach
The two hemispheres are connected by bundles of thick nerve fibers, called commissures. "In the past, it was assumed that the dominant hemisphere transmits inhibitory signals to the other hemisphere via the commissures, thereby removing specific functions in this region," says Onur Güntürkün. However, the interactions between the two hemispheres are both excitatory and inhibitory. "That's why it remains a mystery where exactly functional brain asymmetries come from," says Güntürkün.
In the biopsychology laboratory of Bochum, researchers have therefore approached this question using a new method. They had a color differentiation test performed on the pigeons and extrapolated the activity of individual cells in the visuomotor forebrain of the birds. This brain region processes the information provided by the visual sense and controls the motor functions according to the visual information. In birds, the left hemisphere is dominant for these tasks.
Blocked communication
In order to analyze the influence of inter-hemispheric interactions, Xiao and Güntürkün sometimes blocked the activity of neurons that communicate with the other hemisphere. They monitored the reactions of neurons that usually receive information from the other hemisphere. Thus, they were able to decode the influence of the interaction between the two hemispheres.
The result is as follows: if both brain hemispheres compete for control, the left hemisphere is able to delay the activity of neurons in the right hemisphere. "The right hemisphere is just too late to control the response," says Onur Güntürkün. Researchers have shown that neurons in the left and right hemispheres are also able to synchronize their activity.
A question of timing
"These results show that the domination of the hemisphere is based on a sophisticated mechanism," concludes Onur Güntürkün. "It does not depend on a general inhibitory or excitatory influence, it is rather caused by minimal time delays in the activity of nerve cells in the other hemisphere."
Explore further:
Why the left hemisphere of the brain understands language better than law
More information:
Qian Xiao et al. Asymmetric control of the subdominant hemisphere in pigeons, Cell reports (2018). DOI: 10.1016 / j.celrep.2018.10.011
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