Abdominal positioning interneurons in crayfish: participation in behavioral acts

Area of Science:

• Neuroscience
• Animal Behavior
• Crustacean Physiology

Background:

• Premotor interneurons control complex behaviors in animals.
• Crayfish abdominal positioning involves flexion and extension movements.
• Understanding neural circuits is key to deciphering motor control.

Purpose of the Study:

• Investigate the role of premotor interneurons in crayfish abdominal positioning.
• Determine the contribution of flexion-producing interneurons (FPIs), extension-producing interneurons (EPIs), and mixed output interneurons (MOIs) to motor programs.
• Assess the existence of 'command neurons' in this system.

Main Methods:

• Intracellular recordings from premotor interneurons and motoneurons in semi-intact crayfish preparations.
• Stimulation via depolarizing current injection to classify interneurons.
• Elicitation of fictive behaviors using platform drop/rise.
• Hyperpolarization to silence interneurons and assess their contribution.

Main Results:

• Fewer than half of classified interneurons were active during behavioral episodes.
• Interneuron firing probability was not correlated with stimulus response strength.
• Hyperpolarization revealed that FPIs, EPIs, and MOIs contribute minimally to the overall motor output.
• Many interneurons fired during both flexion and extension behaviors.
• The 'T' cell type was uniquely associated with flexion behaviors.
• Interneuron firing depended on stimulus strength, location, and interneuron location.

Conclusions:

• Crayfish abdominal positioning is controlled by a distributed network of neurons, not by single command neurons.
• Each interneuron contributes a small, probabilistic component to the motor output.
• The 'T' cell is a notable exception, playing a significant role in flexion.