Chapter 2--the spinal generation of phases and cycle duration

Area of Science:

• Neuroscience
• Locomotion
• Spinal Cord Research

Background:

• Locomotion involves coordinated limb movements controlled by spinal rhythm generators.
• During walking, speed changes primarily affect stance duration, not swing phase.
• Central pattern generators (CPGs) in the spinal cord manage locomotor cycle timing and phase transitions.

Purpose of the Study:

• To investigate if the asymmetry in locomotor cycle control is an inherent property of the CPG.
• To determine if rhythm generators for locomotion and scratching share similar control mechanisms.

Main Methods:

• Recorded fictive locomotion and scratching in decerebrate cats (with or without spinal transection).
• Analyzed phase durations and cycle period variations during fictive locomotion and scratching.
• Examined effects of mesencephalic locomotor region stimulation and peripheral nerve stimulation.
• Assessed impact of ankle dorsiflexion on fictive locomotion and scratching.

Main Results:

• Fictive locomotion cycle period predominantly varied with extensor (stance) phase duration, independent of sensory feedback or supraspinal input.
• Stimulation of the mesencephalic locomotor region or peripheral nerves altered the phase/cycle period relationship.
• Fictive scratching cycle period varied mainly with flexion (swing) phase duration.
• Ankle dorsiflexion affected locomotion but not scratching cycle period.

Conclusions:

• The spinal rhythm generator for locomotion possesses a built-in asymmetry in phase control.
• Locomotor and scratching rhythms are regulated by distinct spinal interneuronal circuits.
• Sensory inputs and supraspinal factors can modify, but do not create, the inherent asymmetry in locomotor control.