Body side-specific changes in sensorimotor processing of movement feedback in a walking insect

Area of Science:

• Neuroscience
• Biomechanics
• Insect Locomotion

Background:

• Sensory feedback, particularly from the femoral chordotonal organ (fCO), modulates motor output in insect legs.
• The fCO encodes joint angle, velocity, and acceleration, influencing reflexes like the active reaction (AR).
• ARs assist flexion during active movements and can be modulated by sensory input.

Purpose of the Study:

• To investigate the role of fCO feedback in the differential likelihood of generating ARs during inside versus outside turns in stick insects.
• To analyze how fCO stimulation affects motor output in the femorotibial (FTi) and adjacent leg joints during curve stepping.

Main Methods:

• Electrophysiological recordings of motor output to leg joints (FTi, coxa-trochanter, thorax-coxa) in response to fCO stimulation.
• Analysis of AR probability, timing, and motor neuron activity during simulated inside and outside turns.
• Systematic variation of stimulus parameters (starting angle, velocity, excursion) to assess their influence on AR generation.

Main Results:

• AR probability increased with starting angle and decreased with stimulus velocity, independent of total angular excursion.
• fCO feedback excited levator trochanteris motoneurons in both turn types but protractor coxae motoneurons only during outside turns.
• The transition from stance to swing activity occurred at a consistent angular excursion, regardless of turning direction.

Conclusions:

• fCO feedback processing is dependent on the joint and body side, suggesting a body side-specific gain shift.
• Differential processing of fCO feedback likely underlies the distinct leg kinematics observed during inside and outside turns.
• Further research is needed to identify the sources of sensory input causing these local changes in sensory-motor processing.