Introducing the brain: wandering controls (Introduction)

by David Turell , Monday, September 04, 2023, 17:14 (236 days ago) @ David Turell

Many areas involved:

https://medicalxpress.com/news/2023-09-art-vertebrates-neurons-involved-locomotion.html

"Walking is a complex mechanism involving both automatic processes and conscious control. Its dysfunction can have multiple, sometimes extremely subtle causes, within the motor cortex, brain stem, spinal cord, or muscles.

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"In a study published in Nature Neuroscience, they show that it involves a region classically called the mesencephalic locomotor region, which controls the vigor and speed of movement and transmits the nervous message to the spinal cord via control neurons located in the brainstem.

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"...movement initiation relies on the activation of so-called reticulospinal control neurons, which form an intertwined network in the most posterior part of the brain—the brainstem. These neurons relay nerve signals between the brain and the spinal cord and are essential for motor control of the limbs and trunk and movement coordination.

"Upstream of the reticulospinal neurons is the mesencephalic locomotor region (MLR), which is also essential for locomotion since, in animals, its stimulation triggers forward propulsion. It is found in many vertebrates, including monkeys, guinea pigs, cats, salamanders, and even lampreys.

"'Because the role of the MLR is conserved in many vertebrate species, we assume that it is an ancient region in their evolution—essential for initiating walking, running, flying, or swimming," he adds. "But until now, we didn't know how this region transmits information to the reticulospinal neurons. This prevented us from gaining a global view of the mechanisms that enable the vertebrae to set themselves in motion and, therefore, from pointing out possible anomalies in this fascinating machinery."

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"'We observed that neurons in the mesencephalic locomotor region are stimulated when the animal moves spontaneously, but also in response to a visual stimulus. They project through the pons—the central part of the brain stem—and the medulla to activate a subpopulation of reticulospinal neurons called V2a," Claire Wyart says.

"'These neurons control the finer details of movement, such as starting, stopping, and changing direction. In a way, they give steering instructions. Previous work on mice had revealed that reticulospinal neurons control turning; Martin and Mathilde have discovered the control circuit that triggers forward locomotion."

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"'Quadrupeds can adopt different gaits, such as walking, trotting, or galloping. But aquatic animals also mark gait transitions," Martin Carbo-Tano adds. "We think that MLR has a role to play in this intensification of movement, which we have observed in zebrafish."

'For the first time, this work made it possible to map the neuronal circuits involved in initiating forward movement—a deficient function in patients with Parkinson's disease. This is an essential step in shedding light on the motor control mechanisms upstream of the spinal cord.

"'Because the role of the MLR is conserved in many vertebrate species, we assume that it is an ancient region in their evolution—essential for initiating walking, running, flying, or swimming," he adds. "But until now, we didn't know how this region transmits information to the reticulospinal neurons. This prevented us from gaining a global view of the mechanisms that enable the vertebrae to set themselves in motion and, therefore, from pointing out possible anomalies in this fascinating machinery."

***

"'We observed that neurons in the mesencephalic locomotor region are stimulated when the animal moves spontaneously, but also in response to a visual stimulus. They project through the pons—the central part of the brain stem—and the medulla to activate a subpopulation of reticulospinal neurons called V2a," Claire Wyart says.

"'These neurons control the finer details of movement, such as starting, stopping, and changing direction. In a way, they give steering instructions. Previous work on mice had revealed that reticulospinal neurons control turning; Martin and Mathilde have discovered the control circuit that triggers forward locomotion.'"

Comment: only humans are fully upright walkers. This study adds to the complexity of human evolution. A major evolutionary change in the nervous system to allow the balance mechanism to fully note position of the whole body as maintained by activated muscles in legs and in the upright spinal back. The bony pelvic changes are just part of the equation. The fossils like Lucy show tree climbing shoulders but do not tell us how the ape to human transition really occurred. It was not simple.