Task specificity of local load feedback depends on intersegmental information in an insect walking system

Area of Science:

• Neuroscience
• Biomechanics
• Insect Locomotion

Background:

• Load proprioception via campaniform sensilla (CS) is crucial for generating leg stepping.
• Previous studies in reduced preparations showed direction-dependent reversal of CS feedback effects on motor neurons (MNs).
• The impact of CS feedback on MNs during actual stepping movements remains largely uninvestigated.

Purpose of the Study:

• To investigate the direction-dependent effects of load proprioceptive feedback on leg motor neuron activity during actual fictive stepping.
• To determine if load feedback effects reverse during forward versus backward stepping in stick insects.
• To elucidate the role of intersegmental signals in processing load proprioceptive feedback.

Main Methods:

• Extracellular recordings of protractor and retractor motor neuron activity.
• Load stimulation applied to a single middle leg during fictive forward and backward stepping.
• Analysis of motor neuron activity patterns in response to load stimulation during stance and swing phases.

Main Results:

• During forward stepping, CS stimulation prolonged stance (retractor) activity and induced stance (retractor) activity during the swing phase.
• During backward stepping, CS stimulation prolonged stance (protractor) activity.
• CS stimulation rarely induced stance (protractor) activity during the swing phase in backward stepping, suggesting a lack of intersegmental directional cues.

Conclusions:

• Load proprioceptive feedback effects on motor neurons are direction-dependent during actual stepping.
• Intersegmental signals are critical for the task-specific processing of load proprioceptive feedback during locomotion.
• The absence of intersegmental information impacts the motor response to load feedback during backward stepping swing phase.