Making art, creating things and indulging in creative hobbies are known to make us happier,…
Writing, screwing or throwing darts are just a few of the activities that require a high level of skill. How the brain masters such exquisite movements has now been described in the journal “Nature“by a team of researchers from the University of Basel and the Friedrich Miescher Institute for Biomedical Research. A brainstem circuit map reveals which neurons control fine motor skills in the arm and hand.
Taking a pen and writing our name or picking up a fork to eat spaghetti with tomato sauce are things we take for granted. However, holding a pen properly or bringing spaghetti to your mouth without doing damage requires precise arm movements and a high level of skill.
Underlying all of our motor behavior is a perfect interplay between neurons in the brain, spinal cord and muscles. But what neural circuits control fine motor skills in the arms, hands, and fingers? Professor Silvia Arber’s team has looked at this question in recent work. Neurobiologists who work at both the Biozentrum of the University of Basel and the Friedrich Miescher Institute for Biomedical Research (IMF) have been studying for many years how the nervous system controls motor behavior.
Neurons in the brainstem control fine motor skills
Using a mouse model, the researchers were able to demonstrate that a specific region of the brainstem is responsible for various fine motor activities of the forelimbs. For their investigations, they applied so-called optogenetic and viral methods to mark neurons and observe their activity. This allowed the team to locate four neuronal subpopulations in this region and correlate them with specific functions. For example, one group of neurons have been able to induce damage to the forelimbs, while another group controls the handling of food.
In terms of evolution, the brainstem is the oldest part of the brain and is a direct extension of the spinal cord. The brainstem is an important standard between the higher-order movement planning centers in the brain and the executive circuits of the spinal cord. In the spinal cord, the flow of movement information ultimately reaches motor neurons which are directly connected to muscle cells. These in turn control the movement by contraction. It was only recently that it was discovered that the brainstem consists of numerous areas containing functionally specialized neuronal populations, engaged in the control of various forms of bodily movement.
Brainstem Circuit Map for Fine Motor Skills
In their study, Arber’s team defined the organization of neurons in one of these brainstem regions called the “lateral rostral medulla” (latRM) and mapped out their communication pathways. This allowed researchers to associate different behavioral activities with specific groups of latRM neurons. “Relatively simple actions of the forelimbs, such as foraging, are performed by latRM neurons with direct projections to the spinal cord,” says first author Ludwig Ruder.
The execution of more complex movements of the forelimbs, which also involve the fingers, i.e. grabbing or carrying a piece of food to the mouth, is controlled by latRM neurons with connections to neurons in other regions of the brainstem. “The connections and circuits within the brainstem are essential for more complex motor skills,” says Arber. “The neuronal populations we identified in latRM very specifically control forelimb motor skills. Notably, the generation of complex and precise forelimb movements such as throwing, grabbing or writing requires communication between different regions of the brainstem. “
The control of motor actions is similar in humans and animals
Dividing neuronal populations into different forms of movement based on spatial organization and connectivity provides a better understanding of brainstem function and control of motor behavior, in this case fine motor skills of the arm and hand. Many brainstem neural circuits are similar in humans and animals. It is therefore possible to hypothesize which neuronal populations control which movements or how diseases or injuries can alter fine motor skills or other behaviors in humans.
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