Thorax-Segment- and Leg-Segment-Specific Motor Control for Adaptive Behavior.

Area of Science:

• Neuroscience
• Locomotion Biomechanics
• Animal Behavior

Background:

• Understanding motor program flexibility is crucial for deciphering locomotion control.
• Segmental neural networks coordinate individual leg movements in vertebrates and invertebrates.
• Investigating curve walking in stick insects provides insights into turning mechanics.

Purpose of the Study:

• To investigate the mechanisms of curve walking in the stick insect *Carausius morosus* during optomotor-induced turning.
• To determine if body-side specific changes in leg motor activity extend to all thoracic leg segments.
• To elucidate the role of central pattern generating networks (CPGs) in mediating turning-related motor output modifications.

Main Methods:

• Recorded motor neuron activity in three major leg joints (thorax-coxa, coxa-trochanteral, femur-tibia-tarsus) during curve walking.
• Pharmacologically activated meso- and metathoracic CPGs.
• Analyzed motor output changes in relation to turning direction (inside/outside turns).

Main Results:

• Thorax-coxa joint motor neuron activity showed context-dependent changes based on turning direction.
• Coxa-trochanteral joint motor neuron pools exhibited directional-independent activation/cessation.
• Femur-tibia-tarsus joint motor neuron activity was modified in a turning-direction-dependent manner in one, but not the other, thorax segment.
• Pharmacological activation confirmed that turning-related motor output changes involve local CPG activity.

Conclusions:

• Motor activity changes during curve walking are specific to leg joints and thorax segments.
• These modifications are influenced by turning direction.
• Local CPG activity is the primary mediator of these turning-specific motor adjustments in the meso- and metathorax.