Coordinated spinal locomotor network dynamics emerge from cell-type-specific connectivity patterns

Area of Science:

• Neuroscience
• Computational Biology
• Systems Neuroscience

Background:

• Spinal locomotor circuitry generates complex behaviors like left-right alternation and variable-speed control independently of brain input.
• Existing models inadequately explain rhythmogenesis and recent findings on cell-type-specific connectivity and speed-selective interneurons.

Purpose of the Study:

• To develop and analyze a hierarchy of computational models for spinal locomotor networks.
• To elucidate the core mechanisms of rhythmogenesis and variable-speed control in locomotion.

Main Methods:

• Developed a series of increasingly detailed computational models of the spinal locomotor network.
• Investigated network dynamics, focusing on intersegmental connectivity and interneuron populations.
• Analyzed model behavior to understand emergent locomotion patterns and speed control mechanisms.

Main Results:

• Coordinated locomotion emerges in inhibition-dominated networks with connectivity based on intersegmental phase relationships.
• Variable-speed control is achieved through the recruitment of speed-selective interneuron subpopulations.
• Excitatory connections enhance peak locomotion frequency but can compromise smooth transitions at intermediate speeds, indicating a speed-control trade-off.

Conclusions:

• Network-level interactions within the spinal cord are sufficient for generating coordinated, variable-speed locomotion.
• Provides new interpretations for the roles of intersegmental excitatory and inhibitory connectivity.
• Highlights a fundamental, recruitment-based mechanism for speed control in locomotion.