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Due to the pronounced alternation of right-left and flexor-extensor muscles, different groups of interneurons or "modules" that regulate movement are activated
in a push-pull fashion.
The neural circuits that regulate movement include regions such as the forebrain region, cerebellum, and brainstem, however, the core of motor execution is located in the
spinal cord.
These spinal cord motor circuits, often referred to as central pattern generators (CPGs), autonomously generate rhythms that coordinate muscles
.
The traditional motor loop model focuses on alternation between paired muscles: an excitatory neuron causes an explosion of activity in a muscle, while driving inhibitory neuronal inhibition controls the activity of the neurons of the contralateral muscle, the cycle swings back and forth, and the muscle produces flexion and extension alternates
.
On October 12, 2022, the research team found that the rotational dynamics of nerve fiber activities during the turtle's walking process were confirmed, and the organizational structure characteristics
of the rotational dynamics mode driven by the spinal cord neural circuit were confirmed by the neural network model.
1
Neuronal activity patterns that control rotational dynamics of turtle movement
Through multiple electrodes to record the firing activity of neurons in the lumbar spine of the tortoise, the firing activity of a single neuron is close to the sine wave change characteristics, but the change of the entire neuron population has an unexpected change law: neural activity is constantly circulating through various stages, forming a "ring".
This pattern of activity, known as rotational dynamics, was previously found
in the cortex of nonhuman primates that control arm movement.
Figure 1: The population of neurons that control movement operates in a circular cycle
2
The BSG neural network mode simulates rotational dynamics patterns
a network of interneurons and two or more nerve fibers that control movement.
In this model, neurons are connected almost randomly, but still generate appropriate patterns of activity to drive alternating muscles
.
The activity patterns of the muscles themselves are simpler than those of spinal cord neurons (real or simulated), which means that rotational dynamics patterns are a property of neural circuits, not just a reflection
of muscle dynamics.
The model can quickly and easily adjust the parameters to generate movements
of different intensities and speeds.
By altering the "gain" of these neurons, the researchers identified "accelerator" or "brake" cells that increased or decreased the speed of movement, respectively.
Figure 2: Neural network patterns identify cells that accelerate or slow down motion
3
The BSG neural network model explains the versatile output of a kinematic system
e.
, multifunctional outputs) is the hallmark of
a motion system.
The researchers recorded the electrical activity of nerve fibers during the two classical hindlimb movements of sea turtles, and at the same time adjusted different neuronal populations in the BSG network model according to the gain of two different behaviors, which could induce two activity patterns
of neuronal populations related to different behaviors.
This suggests that the BSG network model is suitable for interpreting the multifunctional output
of spinal cord loops.
Figure 3: Multiple locomotion function outputs of sea turtles
summary
In the past, the rise or fall of neuronal activity in the spinal cord nerve circuit occurred
repeatedly and alternately.
This paper found that the activity of neurons that control movement operates in a circular rotation fashion, which challenges the traditional mode
of motor control.
【References】
1.
https://doi.
org/10.
1038/s41586-022-05293-w
2.
https://doi.
org/10.
1038/d41586-022-02238-1
The images in the article are from references
