Summary: Scientists have uncovered how the vertebral cord helps mimic sensations to allow for soft, deliberate movements. The study uses simulations to demonstrate how circuits in the spinal cord control push reflexes, preventing problems during precise movements like reaching.
This study challenges the idea that activity is only brain-controlled, giving a fresh perspective on how the cervical cord interacts with the mind. The results could help develop better treatments for neurological conditions that affect motor control, such as cerebral palsy and injury.
Important Information:
- The spinal cord is crucial for controlling sensations to facilitate easy activities.
- This lumbar control aids in avoiding movement alterations brought on by reflexes.
- The researches could help with the treatment of motion disorders like cerebral palsy and stroke.
Origin: USC
How did the bodies of animals, including theirs, became quite fine-tuned action systems?
The mystery that Francisco Valero-Cuevas ‘ Lab in the USC Alfred E. Mann Department of Biomedical Engineering, set out to know is how animals coordinate the immortal tug-o-war between spontaneous sensations and smooth volunteer movements.
The Lab’s most recent computational paper, published in the Proceedings of the National Academy of Sciences ( PNAS ), strengthens the field’s focus on the regulation of reflexes during voluntary movements and opens up new avenues for research into how its disruption could lead to motor disorders in neurological conditions like cerebral palsy, Parkinson’s disease, and stroke.  ,
Do you recall having your hip tapped by the physician to check whether you had a strong involuntary knee-jerk reaction? This was done to evaluate your lumbar cord’s expand reflexes, which prevent muscle contraction and give you muscle tone to support your body against gravity, such as quick corrective movements after tripping.
So, how exactly those sensations are modulated or inhibited to allow soft, deliberate movement has been debated since Charles Scott Sherrington’s fundamental work in the 1880s (yes, the 1880s! ).
This new work immediately engages in important debates about how the fairly new human brain and the old spinal cord interact to create soft movements, and how some cerebral conditions interfere with this good balance and result in slow, inaccurate, jerky, etc. actions in neurological problems.
The study, led by Biomedical executive doctoral student Grace Niyo, sheds light on a probable hidden program or hardware at play within the spinal cord that, when working correctly, “modulates” sensations during voluntary activities. According to Niyo, the study proposes” a potentially novel mechanism to modify cervical reflexes at the same spinal cord level as push reflexes.”
Valero-Cuevas, Professor of Biomedical Engineering, Aerospace and Mechanical Engineering, Electrical and Computer Engineering, Computer Science, and Biokinesiology and Physical Therapy at USC, is the equivalent author of the paper” A computing study of how α- to γ-motoneurone credit can alleviate velocity-dependent stretch reflexes during voluntary movements.  ,
Reflexes are sophisticated and traditional low-level information exchange mechanisms that have evolved and changed with modern innovations, such as the human brain. Understanding how they collaborate with the brain is crucial for understanding movement in health and disease. ”  ,
Valero-Cuevas says”, We are constantly benefiting from, and modulating stretch reflexes, whether we realize it or not as we stand, move and act.”
The research of Professor Valero-Cuevas ‘ lab has a focus on understanding how neuromuscular control affects human mobility in both humans and robots.  ,
He states,” We need to recognize the power and significance of the ancient spinal cord, which has allowed all vertebrates to thrive for millions of years before large brains were even possible, despite our brains’ extremely sophisticated brains. We want to know how the spinal cord regulates smooth movements in amphibians and reptiles, even with the least amount of brain control.
” This perspective could have important implications for understanding, and possibly treating, movement disorders in neurological conditions that affect the brain, spinal cord, or both—and also for creating biologically-inspired prostheses or robots that move smoothly using simulated spinal cords”.
The team, under the direction of Niyo, created a biomechanical model of the arm of a macaque monkey in the physics simulator software MuJoCo to test whether and how a spinal circuit can facilitate voluntary movements by modulating or inhibiting movement perturbations brought on by stretch reflexes. The simulation experiment produced over one thousand reaching movements.
The simple stretch reflex rule states that muscles that are stretched will typically oppose the stretch, whereas those that are shortening do not exhibit stretch reflexes.
The first study demonstrated that voluntary arm movements are induced by unmodulated stretch reflexes by creating a self-perturbation. The same neurons in the spinal cord that regulate muscle force were then used to implement a straightforward spinal circuit, which scaled ( i .e., modulated ) the stretch reflex in accordance with their level of muscle excitation. That is, highly excited muscles would have strong stretch reflex responses if stretched, and vice versa.
They discovered that this straightforward rule, which is that it is physiologically possible given the known projections from alpha motoneurones ( also known as collaterals ) to the reflex circuitry, can largely correct the self-perturbations from stretch reflexes and produce smooth and accurate voluntary movements on its own.  ,  ,
One might compare this to “edge computing” from a contemporary engineering perspective, which states that information processing is done at the source ( limb sensors and the spinal cord ) rather than exclusively at the central command center ( the brain ), similar to the way some apps on your phone process data before it is sent to a cloud server.  ,  ,
In a mechanical sense, Valero-Cuevas uses reflex circuitry to simulate the” training wheels on a bicycle that are there to allow you to have fun and catch you when you learn to ride your bicycle.”
These circuits may assist you in developing novel voluntary movements with little interruption, but they also leave the possibility that the brain and cerebellum may develop and learn to control reflexes as your nervous system matures or develops enough experience.  ,
Implications: Niyo claims that this knowledge could serve as a jumping off point for experimentalists to begin looking for and testing for such spinal circuits in addition to improving their understanding of movement disorders. According to Niyo and Valero-Cuevas,” This work could also inspire and guide new therapies at the appropriate level of the nervous system for the treatment of movement disorders like stroke and cerebral palsy.”  ,
Andrew Erwin, a Post-doctoral researcher at the USC Division of Biokinesiology and Physical Therapy, and Lama I. Almofeez, a PhD student at the USC Alfred E. Man Department of Biomedical Engineering, are the study’s additional co-authors.
About this news about neuroscience research
Author: Amy Blumenthal
Source: USC
Contact: Amy Blumenthal – USC
Image: The image is credited to Neuroscience News
Original Research: Open access.
” A computational investigation examines how to minimize velocity-dependent stretch reflexes during voluntary movement by using to motoneurone collateral.” by Francisco Valero-Cuevas et al. PNAS
Abstract
A computational investigation examines how to minimize velocity-dependent stretch reflexes during voluntary movement by using to motoneurone collateral.
The primary motor cortex does not specifically or directly affect the ability of alpha motoneurone ( MN) drive to muscles while moving involuntarily. Rather, α-MN drive emerges from the synthesis and competition among excitatory and inhibitory inputs from multiple descending tracts, spinal interneurons, sensory inputs, and proprioceptive afferents.
In lengthening muscles, velocity-dependent stretch reflexes should be avoided because they enable voluntary movement.
However, it is still unclear how much unmodulated stretch reflexes interfere with voluntary movement and whether or not they are blocked in limbs with numerous multiarticular muscles.
We only applied feedforward-MN commands and additional velocity-dependent stretch reflex feedback to simulate movements of a Rhesus Macaque arm computational model.
We found that velocity-dependent stretch reflex caused movement-specific, typically large and variable disruptions to arm movements.
When using a modulated velocity-dependent stretch reflex feedback ( i), as per the frequently debated ( but unclarified ) idealized alpha-gamma(-) coactivation or ( ii ), as an alternative MN collateral projection to homonymous MNs, these disruptions were significantly reduced. In the mammalian fusimotor system, we come to the conclusion that these MN collaterals are physiologically tenable propriospinal circuits.
These collaterals could still collaborate with α-γ coactivation, and the few skeletofusimotor fibers (β-MNs ) in mammals, to create a flexible fusimotor ecosystem to enable voluntary movement.
By locally and automatically regulating the highly nonlinear neuro-musculo-skeletal mechanics of the limb, these collaterals could be a critical low-level enabler of learning, adaptation, and performance via higher-level brainstem, cerebellar, and cortical mechanisms.
