Gain changes in sensorimotor pathways of the locust leg

Area of Science:

• Neuroscience
• Animal Behavior
• Biophysics

Background:

• Animal leg joint control systems require behavioral flexibility.
• Gain changes in neural control networks are a key aspect of this flexibility.
• The locust femur-tibia (FT) joint control network's circuitry is well-studied, but gain control mechanisms remain unclear due to spontaneous variations.

Purpose of the Study:

• To investigate reproducible changes in the gain of the locust FT joint control network.
• To identify the neuronal basis of gain control in this system.
• To understand how motor activity influences joint feedback regulation.

Main Methods:

• Developed a behavioral preparation in Locusta migratoria (L.) exhibiting reproducible gain changes.
• Recorded resistance reflexes in the FT joint after fictive flight motor activity.
• Measured motoneurone recruitment and synaptic input to motoneurones.
• Recorded from identified pre-motor nonspiking interneurones.

Main Results:

• Fictive flight motor activity significantly decreased FT joint resistance reflex gain (up to 70% reduction).
• Gain reduction primarily affected flexor tibiae muscles more than extensors.
• The decrease in gain resulted from reduced motoneurone recruitment due to diminished synaptic input at the pre-motor network level.
• No changes in motoneurone membrane potential or conductance were observed.

Conclusions:

• The locust FT joint control network exhibits significant, short-term gain modulation following motor activity.
• Gain control is mediated at the pre-motor network level, not directly at the motoneurone.
• This modulation highlights the neural basis of adaptive motor control and behavioral flexibility.