Descending influences on escape behavior and motor pattern in the cockroach

Area of Science:

• Neuroethology
• Animal Behavior
• Locomotion Control

Background:

• Cockroach escape is a rapid, ballistic movement.
• Thoracic and abdominal ganglia control escape behavior.
• The role of descending inputs from the brain and suboesophageal ganglion is unclear.

Purpose of the Study:

• To investigate the influence of descending inputs on cockroach escape behavior.
• To determine if the brain or suboesophageal ganglion are necessary for directional escape turns.
• To characterize the effects of removing descending inputs on leg kinematics and motor neuron activity.

Main Methods:

• Cockroaches were decapitated to remove descending inputs.
• Escape responses were evoked and analyzed.
• Leg movements were quantified, and electromyograms (EMGs) were recorded.
• Descending neural signals were reversibly blocked using a sucrose solution.

Main Results:

• Decapitated cockroaches executed directionally appropriate escape turns.
• A front-to-back gradient of reduced leg movement was observed after decapitation.
• Removal of brain inputs, but not suboesophageal ganglion inputs, mimicked this gradient.
• Reduced leg excursion correlated with decreased fast motor neuron activity.
• Reversible blockage of descending signals confirmed these findings without trauma.

Conclusions:

• Thoracic circuitry is sufficient for directional cockroach escape.
• Descending inputs from the brain modulate the excitability of escape circuitry components.
• Tonic descending inputs are likely crucial for maintaining normal escape response kinematics due to the speed of the behavior.